Publications & patents

Abstracts

  1. Actin is not required for nanotubular protrusions of primary astrocytes grown on metal nano-lawn.
    Gimsa, U; Iglic, A; Fiedler, S; Zwanzig, M; Kralj-Iglic, V; Jonas, L; Gimsa, J. 2007. Molecular Membrane Biology 24(3): 243-255.

    2. Abstract:We used sub-micron metal rod decorated surfaces, 'nano-lawn' structures, as a substrate to study cell-to-cell and cell-to-surface interactions of primary murine astrocytes. These cells form thin membranous tubes with diameters of less than 100 nm and a length of several microns, which make contact to neighboring cells and the substrate during differentiation. While membrane protrusions grow on top of the nano-lawn pillars, nuclei sink to the bottom of the substrate. We observed gondola-like structures along those tubes, suggestive of their function as transport vehicles. Elements of the cytoskeleton such as actin fibers are commonly believed to be essential for triggering the onset and growth of tubular membrane protrusions. A rope-pulling mechanism along actin fibers has recently been proposed to account for the transport or exchange of cellular material between cells. We present evidence for a complementary mechanism that promotes growth and stabilization of the observed tubular protrusions of cell membranes. This mechanism does not require active involvement of actin fibers as the formation of membrane protrusions could not be prevented by suppressing polymerization of actin by latrunculin B. Also theoretically, actin fibers are not essential for the growing and stability of nanotubes since curvature-driven self-assembly of interacting anisotropic raft elements is sufficient for the spontaneous formation of thin nano-tubular membrane protrusions.


  2. Online monitoring of cell metabolism for studying pharmacodynamic effects.
    Thedinga, E; Kob, A; Holst, H; Keuer, A; Drechsler, S; Niendorf, R; Baumann, W; Freund, I; Lehmann, M; Ehret, R. 2007. Toxicol. Appl. Pharmacol. 220(1):33-44.

    3. Abstract: To characterize modes of action of substances and their cytotoxic effects Bionas GmbH has developed a new screening system to allow the continuous recording of how an active substance can act (Bionas 2500 analyzing system). In the pharmaceutical industry it is important to acquire as much information as possible about the metabolic effects of an active substance. Most classical pre-clinical studies are very expensive and time-consuming. Often they are so-called end-point tests which require many individual tests before approximate statements can be made about how an effect takes its course. With the Bionas 2500 analyzing system metabolically relevant data including oxygen consumption, acidification rate and the adhesion (cell impedance) of cells can be measured in parallel, online and label-free. Using e.g. ion-sensitive field effect-transistors (ISFET) and electrode structures it is possible to observe metabolic parameters non-invasively and continuously over longer periods of time. The system has already been established for several cell models, cell lines as well as primary cells. It also offers the advantage that regenerative effects can be observed during the same test run.


  3. Simplified equations for the transmembrane potential induced in ellipsoidal cells of rotational symmetry.
    Maswiwat, K; Wachner, D; Warnke, R; Gimsa, J. 2007. JOURNAL OF PHYSICS D-APPLIED PHYSICS 40(3): 914-923.

    4. Abstract: The induction of transmembrane potentials (Delta phi) by an external field is the basis of numerous applications in biotechnology, cell-technology and medicine. We have developed new, simplified analytical equations that avoid the complicated description by the depolarizing factors. The equations apply to the Delta phi induced in cells resembling ellipsoids of rotation, i.e. spheroids by homogeneous dc or ac fields. They will be especially useful for experimental scientists. The equations describe the dependence of the Delta phi on the electric media properties, the field frequency and the axis ratio for oblate and prolate spheroids for which the symmetry semiaxis (c) is shorter and longer than the other two semiaxes (a and b, with a = b), respectively. According to the Schwan equation, an electric field E may induce a maximum Delta phi of 1.5aE at the poles of a spherical cell. For the poles of spheroidal cells, the maxima can be easily described by Delta phi = (a + 2c) E/2 and Delta phi = a(a + 2c) E/(a + c) for fields oriented along and perpendicular to the symmetry axis, respectively. For practically important shapes the error in the magnitude of Delta phi is smaller than 5% except along the c-axis for axis ratios larger than 2. Nevertheless, the errors vanish for the three limiting shapes of infinitely thin disc, sphere and cylinder.


  4. On the temperature dependence of the dielectric membrane properties of human red blood cells.
    Sudsiri, J; Wachner, D; Gimsa J. 2007. Bioelectrochemistry 70(1):134-40.

    5. Abstract: Electrorotation (ER) spectra of human red blood cells (HRBCs) have been recorded in the frequency range from 10 kHz to 250 MHz in a 4-electrode microchip chamber. The cells were suspended at conductivities in the range from 0.02 to 3.00 S/m (corresponding to an ionic strength range from 1.6 to 343 mM) at temperatures between 10 degrees C and 35 degrees C. Generally, the characteristic frequencies as well as the rotation speeds of the first (membrane-dispersion) and second ER peaks increased with temperature. The rotation speed increase was largely correlated to the temperature dependence of the medium viscosity. Standard temperature dependencies were assumed for the conductivities and permittivities of cytoplasm, membrane, and external solution to explain the frequency shifts, starting from the cell parameters of Gimsa et al. [Gimsa et al., 1996, Biophys. J. 71: 495-506.]. The membrane capacitance was assumed to be temperature independent, based on the permittivity of alkyl-chains. Under these assumptions, the spectra could be well fitted only in a narrow temperature range around 20 degrees C. The temperature dependence of the first characteristic frequency was much stronger than predicted. In addition, around 15 degrees C, an anomalously high rotation speed was observed for the first peak at low external conductivities. Interestingly, this finding corresponds to the change in the chloride transport rate described by Brahm [Brahm, 1977, J. Gen. Physiol. 70: 283-306.].


  5. A new exposure system for the in vitro detection of GHz field effects on neuronal networks.
    Koester, P; Sakowski, J; Baumann, W; Glock, HW; Gimsa J. 2007. Bioelectrochemistry 70(1):104-14.

    6. Abstract: The possible effects of high-frequency electromagnetic fields (EMF) on biological systems are a subject of public concern and scientific discussion. It is generally accepted that the absorption of part of the field energy may cause a temperature rise in biological tissue. Nevertheless, our setup aims to detect possible athermal effects on the electric activity of neuronal in vitro networks. Such networks were formed by primary neurons derived from the murine frontal cortex and cultivated on micro-sensor chips. The action potentials of the neurons were detected in real time by an integrated, electrically passive microelectrode array. For EMF exposure, the chips were introduced into a rectangular wave-guide that could be operated in the propagating or standing wave modes. The drive signals were either continuous waves (1.9-2.2 GHz) or a generic mobile phone signal (UMTS-standard) of up to approximately 8 W. An on-chip sensor allowed the temperature progression to be recorded. In addition, ISFETs and Clark-like electrodes were integrated for the on-chip detection of pH and O(2), respectively.


  6. On the field distribution in electrorotation chambers — Influence of electrode shape.
    Maswiwat, K.; Holtappels, M.; Gimsa, J. 2006. Electrochimica Acta 51: 5215-5220.

    7. Abstract: The electrorotation method can be applied to characterize the passive electric properties of individual cells or particles. For this, their frequencydependent speed of rotation is registered microscopically. Commonly, object rotation is induced in harmonic rotating fields which are generated in four electrode chambers. The rotation speed of the objects is proportional to the square of the field strength. In this study, we calculated the two-dimensional electric field distribution in electrorotation chips using the FEMLAB finite element program (Comsol, Sweden). For reasons of symmetry, a perfectly circular field is generated at the centers of the four electrode chambers. Nevertheless, the field strength is reduced with respect to the quotient of electrode voltage and distance for any electrode shape. Distant from the center, the field polarization is elliptical with an eccentricity increasing with the distance to the center. For optimizing the electrode shape, the deviations in torques for given distances from the center have been calculated. These deviations have been compared for various electrode shapes in order to find an optimal chip design. Another criterion was a large electrode distance in the corners of the electrode arrangement in order to avoid field hot spots and to minimize dielectrophoretic particle collection.


  7. Characterization of Electrodes for Deep Brain Stimulation.
    Schreiber, U; Gimsa, U; Gimsa, J; van Rienen U. 2006. Proceedings of the Sixth International Conference on Computational Elektromagnetics (CEM 2006 - VDE-Conferences), Aachen, 4-6 April 2006, pp. 229, ISBN 3-8007-2957-1.

    8. Abstract: Several neurological diseases, such as Parkinson’s disease, are characterized by a synchronization of ensembles of oscillatory neurons in particular brain areas, where the normal electric activity is supposed to be uncorrelated. The electric stimulation of these brain neurons with pulsed signals, the so-called Deep Brain Stimulation (DBS), counteracts the symptoms of these diseases. Despite its therapeutic application, the mechanisms of DBS and its effect on the neuronal activity are still not fully resolved yet. In DBS, different parameters can be varied, e.g. the way multipolar electrodes are driven (unipolar, bipolar, …), the pulse width, the frequency or the signal amplitude. A very important variable is the geometry of the implanted electrodes. As geometry determines the field in the tissue, cell damage could be inflicted if the field strength around the electrode is too high. Characterization of the electrodes for DBS is necessary to allow for a safe and reproducible application of DBS with respect to the applied voltage or current in a given external medium . In this paper, cell constants, i.e. geometry factors relating the electrode impedance to the specific medium conductivity, were calculated to determine the electrode voltage for a given stimulation current. Nevertheless, for electrodes of the same cell constant but of different geometry, current and field distributions may be very dissimilar. We found geometry-dependent limiting values of the stimulation current, above which electric tissue damage may occur. These values limit the reach of the stimulation signal for a given electrode geometry.


  8. The influence of the molecular structure of lipid membranes on the electric field distribution and energy absorption.
    Simeonova, M; Gimsa, J. 2006. Bioelectromagnetics 27(8):652-66.

    9. Abstract: We consider the influence of the molecular structure of phospholipid membranes on their dielectric properties in the radio frequency range. Membranes have a stratified dielectric structure on the submolecular level, with the lipid chains forming a central hydrophobic layer enclosed by the polar headgroups (HGs) and bound water layers. In our numerical model, isotropic permittivities of 2.2 and 48.8 were assigned to the lipid chain and bound water layers, respectively. The HG region was assumed to possess an anisotropic static permittivity with 142.2 and 30.2 in the tangential and normal directions, respectively. The permittivities of the HG and bound water regions have been assumed to disperse at frequencies around 51 and 345 MHz to become 2.2 and 1.8, respectively, in both the normal and tangential directions. Electric field distribution and absorption were calculated for phospholipid vesicles with 75 nm radius as an example. Significant absorption has been obtained in the HG and bound water regions. Averaging the membrane absorption over the layers resulted in a decreased absorption below 1 GHz but a more than 10-fold increase above 1 GHz, compared to a model with a homogeneous membrane of averaged properties. We propose single particle dielectric spectroscopy by AC electrokinetics at low-bulk medium conductivities for an experimental verification of our model.


  9. Measurement of electrical activity of long-term mammalian neuronal networks on semiconductor neurosensor chips and comparison with conventional microelectrode arrays
    Krause, G; Lehmann, S; Lehmann, M; Freund, I; Schreiber, E; Baumann, W. 2006. Biosensors & Bioelectronics 21 (7): 1272-1282.

    10. Abstract: Based on complementary metal-oxide semiconductor (CMOS) technology a neurosensor chip with passive palladium electrodes was developed. The CMOS technology allows a high reproducibility of the sensors as well as miniaturisation and the on-chip integration of electronics. Networks of primary neurones were taken from murine foetal spinal cord (day 14) and frontal cortex (day 15) tissues and cultured on the silicon surface in a chamber volume of 200 mu l with 7 mm diameter. Measurements were performed between days 15 and 59 in vitro. Signals were recorded from both types of cultures. To test the capability of the system to detect pharmacologically induced activity changes two established neuromodulators were applied. The GABA(A)-receptor blocker bicuculline was applied to both tissue cultures, the glycine-receptor blocker strychnine to spinal cord cultures. Four network frequency parameters were analysed: spike rate (SR), burst rate (BR), frequency in bursts (FiB) and peak frequency in bursts (PFiB). Significant changes of spike rate and burst rate were measured with spinal cord cultures after bicuculline application. Significant changes of frequency in bursts and peak frequency in bursts were observed with frontal cortex cultures after bicuculline application. Significant changes of spike rate and frequency in bursts were recorded with spinal cord cultures after strychnine application. These results were compared with results achieved in the same laboratory by using glass-microelectrode arrays (MEAs). This comparison showed for spinal cord similar native spike and burst rate, but higher mean frequency and peak frequency in bursts, whereas frontal cortex activity had higher spike and burst rate and peak frequency in bursts. Application of bicuculline or strychnine to spinal cord networks showed stronger effects on MEAs, whereas with frontal cortex networks the modulation of activity was similar after application of bicuculline.


  10. Dielectric anisotropy, volume potential anomalies and the persistent Maxwellian equivalent body
    Simeonova, M; Gimsa, J. 2005. J. Phys.: Condens. Matter 17(50):7817-7831.

    11. Abstract: Potentially, lipid membranes possess a high tangential conductivity and permittivity due to their surface charges and the in-plane orientation of the headgroup dipoles. Electrically, membranes exhibit a sandwich structure with a largely isotropic centre formed by the fatty acid chains and confined by two anisotropic headgroup layers. Accordingly, we described spherical vesicles by an aqueous core covered by three shells. For a theoretical comparison, models with an anisotropic single shell and anisotropic homogeneous spheres were also considered. Two effects can be clearly demonstrated. (1) High tangential conductivities or permittivities may lead to cyclic variations in the phase of the electric potential in the radial direction, resulting in a hemi-shell structure of the electric potential inside the objects with oppositely charged facets. The thickness of the anisotropic shell restricts the number of phase oscillations. (2) Despite the strong local field inhomogeneities, an isotropic homogeneous Maxwellian equivalent body with an identical external field distribution exists for any of the anisotropic models. Its properties can be found from a comparison of the numerically calculated surface potential and the classical expression of the Clausius–Mossotti factor at any given frequency. The permittivity conductivity pairs obtained exhibit a sigmoidal-like frequency dependence.


  11. Excluded volume driven counterion condensation inside nanotubes in a concave electrical double layer model.
    Bohinc, K; Gimsa, J; Kralj-Iglic, V; Slivnik, T; Iglic, A. 2005. Bioelectrochemistry 67(1):91-9.

    12. Abstract: The physical properties of organic nanotubes attract increasing attention due to their potential benefit in technology, biology and medicine. We study the effect of ion size on the electrical properties of cylindrical nanotubes filled with electrolyte solution within a modified Poisson-Boltzmann (PB) approach. For comparison purposes, small hollow nanospheres filled with electrolyte solution are considered. The finite size of the particles in the inner electrolyte solution is described by the excluded volume effect within a lattice statistics approach. We found that an increased ion size reduces the number of counterions near the charged inner surface of the nanotube, leading to an enlarged electrostatic surface potential. The concentration of counterions close to the inner surface saturates for higher surface charge densities and larger ions. In the case of saturation, the closest counterion packing is achieved, all lattice sites near the surface are occupied and an actual counterion condensation is observed. By contrast, the counterion concentration at the axis of the nanotube steadily increases with increasing surface charge density. This growth is more pronounced for smaller nanotube radii and larger ions. At larger nanotube radii for small ion size counterion condensation may also be observed according to the Tsao criterion, i.e. the counterion concentration at the centre is independent of the number of counterions in the system. With decreasing radius the Tsao condensation effect is shifted towards physiologically unrealistic surface charge densities.


  12. New insights into the nanometer-scaled cell-surface interspace by cell-sensor measurements
    Lehmann, M; Baumann, W. 2005. Experimental Cell Research 305 (2): 374-382.

    13. Abstract: The culture of adherent cells on solid surfaces is an established in vitro method, and the adhesion process of a cell is considered as an important trigger for many cellular processes (e.g., polarity and tumor genesis). However, not all of the eliciting biochemical or biophysical reactions are yet understood. Interestingly, there are not much experimental data about the impact that the interspace between an adherent cell and the (solid) substrate has on the cell's behavior. This interspace is mainly built by the basolateral side of epithelial cells and the substrate. This paper gives some new results of non-invasive and non-optical measurements in the interspace. The measurements were made with silicon cell-sensor hybrids. Measurements of acidification, adhesion, and respiration are analyzed in view of the situation in the interspace. The results show that, in general, the release of an ion or molecule on the basolateral side can have much more influence on the biophysical situation than a release of an ion or molecule on the apical side. In particular, the apical acidification (i.e., amount of extruded protons) of, e.g., epithelial tumor cells is several orders of magnitude higher than the basolateral acidification. These experimental results are a simple consequence of the fact that the basolateral volume of the interspace is several orders of magnitudes smaller than the apical volume. These results have the following consequences for the cell adhesion: a) static situation: if a cell is already adhered to a solid substrate, the basolateral and apical release and uptake of molecules have to be considered in a very differentiated way; b) dynamic situation: if the cell is adhering to the substrate, the then built basolateral side changes in a much stronger way than the apical side. This effect is here discussed as a possible eliciting and general mechanism for essential intracellular changes.


  13. Choosing electrodes for deep brain stimulation experiments - electrochemical considerations
    Gimsa, J; Habel, B; Schreiber, U; van Rienen, U; Strauss, U; Gimsa, U. 2005. Journal of neuroscience methods 142 (2): 251-265.

    14. Abstract: Deep brain stimulation (DBS) is a therapy of movement disorders including Parkinson's disease (PD). Commercially available electrodes for animal models of Parkinson's disease vary in geometry and material. We characterized such electrodes and found a drift in their properties within minutes and up to about 60 h after immersion in cell culture medium, both with and without a stimulation signal. Electrode properties could largely be restored by proteolytic treatment for platinum/iridium electrodes but not for stainless steel ones. Short-term drift and irreversible aging could be followed by impedance measurements. Aging was accompanied by metal corrosion and erosion of the plastic insulation. For both materials, the degradation rates depended on the current density at the electrode surfaces. Fourier analysis of the DBS pulse (60 mus, repetition rate 130Hz) revealed harmonic frequencies spanning a band of more than three decades, with significant harmonics up to the MHz range. The band is located in a window imposed by electrode processes and capacitive cell membrane bridging at the low and high frequency ends, respectively. Even though electrode processes are reduced at higher frequencies they only vanish above 1 MHz and cannot be avoided. Therefore, the use of inert electrode materials is of special importance. The neurotoxicity of iron makes avoiding stainless steel electrodes imperative. Future developments need to avoid the use of corrosive materials and current density hot spots at the electrode surface, and to reduce low frequency components in the DBS pulses in order to diminish electrode processes.


  14. Estimating the subcellular absorption of electric field energy: equations for an ellipsoidal single shell model.
    Wachner, D; Simeonova, M; Gimsa, J. 2002. BIOELECTROCHEMISTRY 56(1-2): 211-213.

    15. Abstract: An oriented single shell model is used to describe the absorption of electric field energy for a cell of the general ellipsoidal shape exposed to a homogeneous AC-field. A finite element approach alLowed us to derive characteristic equations describing the dependence of the field distribution on the cell geometry, the electric properties of the structural media, membrane and bulk solutions, as well as on the field frequency with a subcellular resolution. Finally, equations were derived for the absorption at certain sites of the model. The model allows for the introduction of frequency-dependent cellular media properties. Experimentally, the new cell parameters can be verified by dielectric single-cell spectroscopy. (C) 2002 Elsevier Science B.V. All rights reserved.


  15. Cellular absorption of electric field energy: influence of molecular properties of the cytoplasm.
    Simeonova, M; Wachner, D; Gimsa, J. 2002. BIOELECTROCHEMISTRY 56 (1-2): 215-218.

    16. Abstract: Molecular dispersions may significantly alter the frequency dependence of structural polarizations. Consequently, the molecular properties cannot be neglected when the energy absorption is calculated with a subcellular resolution. Our example presents calculations that explain the absorption in single human red blood cells. The molecular properties of the cytoplasm have been derived from literature data on the impedance of Hb suspensions. The resulting cell properties were then compared to own data obtained by single cell dielectric spectroscopy. (C) 2002 Elsevier Science B.V. All rights reserved.


  16. On the analytical description of transmembrane voltage induced on spheroidal cells with zero membrane conductance.
    Gimsa, J; Wachner, D. 2001. EUROPEAN BIOPHYSICS JOURNAL WITH BIOPHYSICS LETTERS 30 (6): 463-466.

    17. Abstract: We present analytical equations for the transmembrane voltage (Delta Phi) induced by a homogeneous field on oriented cells of spheroidal shape in spherical coordinates. For simplicity, a nonconductive membrane and a highly polarizable cytoplasm were assumed. Under these conditions, the cell's polarizability is determined by the nonconductive membrane. For symmetry reasons the surface of the highly polarizable cytoplasm can be assumed to be at 0 V. Since the cell is of ellipsoidal shape its effective local field, i.e. the field of its Maxwellian equivalent body, must be constant. This allows for a simple description of the potential at the external membrane side, directly leading to Delta Phi. The dependence of Delta Phi on cell size and shape as well as on the location of the considered membrane site is described for both possible orientations of the symmetry axis, parallel and perpendicular to the external field, respectively.


  17. Analytical description of the transmembrane voltage induced on arbitrarily oriented ellipsoidal and cylindrical cells.
    Gimsa, J; Wachner, D. 2001. BIOPHYSICAL JOURNAL 81 (4): 1888-1896.

    18. Abstract: We present an analytical equation for the transmembrane voltage (Delta phi) induced by a homogeneous AC field on arbitrarily oriented cells of the general ellipsoidal shape. The equation generalizes the Schwan equation for spherical cells and describes the dependence of Delta phi on field frequency, cell size and shape, membrane capacitance, conductivities of cytoplasm, membrane and external medium, the location of the membrane site under consideration, and on the orientation of the cell with respect to the field. The derivation is based on the fact that the cytoplasm and the Maxwellian equivalent body of the whole cell are both of a general ellipsoidal shape and must thus exhibit constant local fields. The constant fields allow for a relatively simple description of the potentials on the internal and external membrane sides, leading to Delta phi. For this, the properties of cytoplasm, membrane, and external medium have been introduced into a special, finite element model. We found that AO can be unambiguously defined for non-spherical cells, provided that the membrane thickness is thin in comparison to the cell dimensions.


  18. Simultaneous measurement of cellular respiration and acidification with a single CMOS ISFET.
    Lehmann, M; Baumann, W; Brischwein, M; Gahle, HJ; Freund, I; Ehret, R; Drechsler, S; Palzer, H; Kleintges, M; Sieben, U; Wolf, B. 2001. BIOSENSORS & BIOELECTRONICS 16 (3): 195-203.

    19. Abstract: In vivo, the pH value and oxygen partial pressure are the most important physico-chemical parameters in the microenvironment of human tissues. In vitro, the extracellular acidification rate of cell cultures is an indicator of global cellular metabolism, while the rate of oxygen consumption is a measure of mitochondrial activity. Earlier approaches had the disadvantage that these two values had to be measured with two separate sensors at different loci within the tissue or cell culture. Furthermore, conventional Clark-type oxygen sensors are not very compatible for miniaturisation, making it impossible to measure at small cell volumes or even at the single cell level. We have, therefore, developed an ISFET based sensor structure which is able to measure both pH and oxygen partial pressure. This sensor structure was tested in vitro for simultaneous records of cellular acidification and respiration rates at the same site within the cell culture. This sensor is manufactured by a CMOS-process.


  19. Multiparametric microsensor chips for screening applications.
    Ehret, R; Baumann, W; Brischwein, M; Lehmann, M; Henning, T; Freund, I; Drechsler, S; Friedrich, U; Hubert, ML; Motrescu, E; Kob, A; Palzer, H; Grothe, H; Wolf, B. 2001. FRESENIUS JOURNAL OF ANALYTICAL CHEMISTRY 369 (1): 30-35.

    20. Abstract: The identification of drug targets for pharmaceutical screening can be greatly accelerated by gene databases and expression studies. The identification of leading compounds from growing libraries is realized by high throughput screening platforms. Subsequently, for optimization and validation of identified leading compounds studies of their functionality have to be carried out, and just these functionality tests are a limiting factor. A rigorous preselection of identified compounds by in vitro cellular screening is necessary prior to using the drug candidates for the further time consuming and expensive stage, e.g. in animal models. Our efforts are focused to the parallel development, adaptation and integration of different microelectronic sensors into miniaturized biochips for a multiparametric, functional on-line analysis of living cells in physiologically environments. Parallel and on-line acquisition of data related to different cellular targets is required for advanced stages of drug screening and for economizing animal tests.


  20. Approach to a multiparametric sensor-chip-based tumor chemosensitivity assay.
    Henning, T; Brischwein, M; Baumann, W; Ehret, R; Freund, I; Kammerer, R; Lehmann, M; Schwinde, A; Wolf, B. 2001. ANTI-CANCER DRUGS 12 (1): 21-32.

    21. Abstract: Although not widely practiced by oncologists, in vitro tumor chemosensitivity assays (TCA) have proved to increase the lifetime of tumor patients in prospective clinical trials. By individualizing cancer therapy, they can support the clinician's decision which is usually based on empirically retrieved data and thereby prevent inadequate chemotherapy. We present the first results of a new sensor-chip-based technology which might be useful for a multiparametric TCA, In particular, the aspect of dynamic on-line data generation on intact cellular specimens is a major difference to alternative assays. A series of experiments has been performed on cell lines and human tumor explants, Cell cultures and tumor tissue explants were placed on miniaturized silicon and glass sensor chips. The sensor data currently analyze metabolic profiles (rates of extracellular acidification and cellular oxygen consumption) and changes in cell morphology (monitoring of electric impedance). With the cell lines, drug-associated cellular signals have been detected with all three parameters, while primary explants so far caused metabolic responses only. In particular, cellular respiration or mitochondrial activity seems to be a most sensitive indicator of acute cytotoxic effects. The experimental results were achieved using different test versions. Besides giving a status report, the theoretical potential and current problems of sensor chip technology in TCA is discussed.


  21. A comprehensive approach to electro-orientation, electrodeformation, dielectrophoresis, and electrorotation of ellipsoidal particles and biological cells.
    Gimsa, J. 2001. BIOELECTROCHEMISTRY 54 (1): 23-31.

    22. Abstract: Suspended cells may respond to AC polarization by orienting, deforming, moving or rotating. For modeling of ellipsoidal cells, a new dipole approach is proposed. Along each of the principal axis of the model, three finite elements of arbitrary but equal cross-sectional area for the interior, low conductive membrane shell and exterior are assumed. The length of the external medium elements is defined by influential radii which are related to the depolarizing factors. The model predicts the potential at the ellipsoid's surface leading to the induced dipole moment. The moment obtained is identical to the Laplace approach for homogeneous ellipsoids; in the single-shell case, it is slightly different. The reason is the constant shell thickness which overcomes the confocal thickness necessary for the Laplace solution. Expressions for electro-orientation, deformation, dielectrophoresis, and electrorotation are derived. In linearly and circularly polarized fields, different orientation spectra are predicted to occur. While in linearly polarized AC fields, particles are oriented along their axis of highest polarizability, in circularly polarized fields, the axis of Lowest polarizability is oriented perpendicular to the plane of field rotation. Based on this finding, a new electro-orientation method is proposed. In dielectrophoresis and electrorotation, reorientations are predicted which lead to discontinuous spectra. (C) 2001 Elsevier Science B.V. All rights reserved.


  22. Critical analysis of the impedance method for the evaluation of permittivity and conductivity of the plasma membrane.
    Bonincontro, A; Gimsa, J; Risuleo, G; Rosa, V. 2000. BIOLOGICHESKIE MEMBRANY 17 (1): 102-106.

    23. Abstract: We report a critical analysis of a typical method of dielectric spectroscopy consisting in impedance measurements as a function of frequency. Experimental data were obtained by measuring impedance on human erythrocyte suspensions. Since these cells do not have a nucleus they represent an ideal material for the application of the well established single shell model. This allows the evaluation of permittivity and conductivity of the plasma membrane. We discuss the influence on the reliability of results of parameters such as fractional volume, average dimensions and membrane thickness of cells.


  23. Neue Lichtstreutechniken erfassen bisher unzugängliche Teilchenparameter.
    LIPPERT, S; WACHNER, D; GIMSA, J. 2000. Humboldt-Spektrum 1/00 7:54-57.

    24. Abstract: Die Kombination einer speziellen Laser-Doppler Methode mit der Dielektrophorese (DP) zur Dielektrophoretischen Phasenanalytischen Lichtstreuung (DPALS) und der dynamischen Lichtstreuung mit der Elektrorotation (ER) zur Elektrorotationslichtstreuung (ERLS) erschließt den Lichtstreutechniken den Zugang zu Teilcheneigenschaften, wie z.B. Kompartimentierung, Volumen- und Oberflächenleitfähigkeit, und der dielektrischen Spektroskopie den submikroskopischen Partikelgrößenbereich. Die neuen Messmthoden wurden im Labor von Priv.-Doz. Dr. J. Gimsa, Institut für Biologie der Humboldt-Universität zu Berlin, entwickelt. Ein Prototyp des ERLS-Messplatzes wird auf der Achema 2000 vorgestellt.


  24. Non-invasive measurement of cell membrane associated proton gradients by ion-sensitive field effect transistor arrays for microphysiological and bioelectronical applications.
    Lehmann, M; Baumann, W; Brischwein, M; Ehret, R; Kraus, M; Schwinde, A; Bitzenhofer, M; Freund, I; Wolf, B. 2000. BIOSENSORS & BIOELECTRONICS 15 (3-4): 117-124.

    25. Abstract: The pH in the cellular microenvironment (pH(M)) is an important regulator of cell-to-cell and cell-to-host interactions. Additionally the extracellular acidification rate of a cell culture is an important indicator of global cellular metabolism. In a new approach a biocompatible ion-sensitive field effect transistor (ISFET)-array was developed to measure the pH(M) close to a surface and the global extracellular acidification rate at the same time. This ISFET-array is part of a new multiparametric microsensor chip. The paper highlights some basic applications of this method for in-vitro measurements. Using a fluid perfusion system for cell culture media, it is possible to measure the pH(M) of few (five to ten) adherent tumor cells in a distance of 10-100 nm from the cell plasma membrane. Experiments showed a pH(M)-value of 6.68 +/- 0.06 pH. Further experiments suggest that both the low pH, and the extracellular acidification rate of the examined tumor cell line are mainly built up by glycolysis.


  25. A polarization model overcoming the geometric restrictions of the laplace solution for spheroidal cells: Obtaining new equations for field-induced forces and transmembrane potential.
    Gimsa, J; Wachner, D. 1999. BIOPHYSICAL JOURNAL 77 (3): 1316-1326.

    26. Abstract: We present a new model for a variety of electric polarization effects on oblate and prolate homogeneous and single-shell spheroids. For homogeneous spheroids the model is identical to the Laplace model. For single-shell spheres of cell-like geometry the calculated difference of the induced dipole moments is in the thousandths range. To solve Laplace's equation for nonspherical single-shell objects it is necessary to assume a confocal shell, which results in different cell membrane properties in the pole and equator regions, respectively. Our alternative model addresses this drawback. It assumes that the disturbance of the external field due to polarization may project into the medium to a characteristic distance, the influential radius. This parameter is related to the axis ratio of the spheroid over the depolarizing factors and allows us to determine the geometry for a finite resistor-capacitor model. From this model the potential at the spheroid's surface is obtained and, consequently, the local field inside a homogeneous spheroid is determined. In the single-shell case, this is the effective local field of an equivalent homogeneous spheroid. Finally, integration over the volume yields the frequency-dependent induced dipole moment. The resistor-capacitor approach alLowed us to find simple equations for the critical and characteristic frequencies, force plateaus and peak heights of deformation, dielectrophoresis and electrorotation for homogeneous and single-shell spheroids, and a more generalized equation for the induced transmembrane potential of spheroidal cells.


  26. New light-scattering and field-trapping methods access the internal electric structure of submicron particles, like influenza viruses.
    Gimsa, J. 1999. ELECTRICAL BIOIMPEDANCE METHODS: APPLICATIONS TO MEDICINE AND BIOTECHNOLOGY 873: 287-298.

    27. Book series title: ANNALS OF THE NEW YORK ACADEMY OF SCIENCES

    Abstract: A variety of AC-electrokinetic held effects can be exploited for handling or electric characterization of microscopic and submicroscopic particles, like cells, organelles, supramolecular structures, and artificial colloids, Despite the fact that dielectric spectroscopy methods by AC-electrokinetics, like common impedance methods, are based on the impedance properties of the different constituents of the particles, the first methods yield higher parameter resolutions. A drawback of the electrokinetic methods was that they required microscopic observability of field-induced particle movements. New AC-electrokinetic methods like electrorotational light scattering (ERLS), dielectrophoretic phase-analysis light scattering (DPALS), and dielectrophoretic field trapping (DFT) solve this problem and access the submicroscopic particle range. This paper gives an introduction to the new methods and presents measurements on influenza viruses. To develop a dielectric virus model, experiments of ERLS were combined with DFT of viruses in microstructured electric-field cages, The model assumes a spherical virus with a radius of 50 nm and a single-shell dielectric structure, The shell thickness of 18 nm summarizes the dimensions of the lipid and viral surface protein layers, For this model, the conductivities of core and shell of 0.1 mS/m and 0.1 mu S/m, respectively, and the relative permittivities of 30 and 80, respectively, were obtained.


  27. Particle characterization by AC electrokinetic phenomena 2. Dielectrophoresis of Latex particles measured by dielectrophoretic phase analysis light scattering (DPALS).
    Eppmann, P; Pruger, B; Gimsa, J. 1999. COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS 149 (1-3): 443-449.

    28. Abstract: Particle polarization in AC fields depends on the temporal and spatial properties of the inducing field and on the dielectric properties of the suspension medium and the particles. In inhomogeneous fields the interaction of the induced dipole moment with the inducing field may give rise to particle translation (dielectrophoresis, DP). The frequency dependence of DP is mediated by the dispersions of different interfacial polarization processes. Consequently, DP spectroscopy yields information on internal particle structures. Common methods microscopically analyze the frequency behavior of the induced motion. Phase analysis light scattering (PALS) is a suitable light scattering method for the registration of extremely slow particle translation. We used PALS to analyze the DP behavior of polystyrene Latex particles in an optical two-electrode chamber. The dielectric particle data obtained are in correspondence to those of the literature. Our method offers statistical significance and computerized operation for dielectric particle spectroscopy. (C) 1999 Elsevier Science B.V. All rights reserved.


  28. Particle characterization by AC-electrokinetic phenomena: 1. A short introduction to dielectrophoresis (DP) and electrorotation (ER).
    Gimsa, J. 1999. COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS 149 (1-3): 451-459.

    29. Abstract: When the response of a particle suspension to an external electric field is analyzed, measurement of the frequency dependence widens the parameter space and enables access to the inherent electric properties of the particles or, for known electric properties, to layer thicknesses, etc. The common impedance method registers the direct electric response to an applied field, whereas dielectrophoresis (DP) and electrorotation (ER) analyze the electrokinetic response of single particles. Since all responses are based on the same principles of interfacial polarization they can generally be described by a unified theory. This is demonstrated by a simple resistor-capacitor model describing the interdependence of the three methods. While the methods generally yield the same information, the particle properties are more clearly reflected in DP and ER spectra. The reason is that, in contrast to impedance, the latter methods are differential; i.e., they are based on the polarizability difference between the particles and the medium. Recently, a main disadvantage of the single particle methods, namely the limited external conductivity and frequency, was overcome by ultra-microelectrode chambers. Another drawback was the requirement of tedious microscopic measurements on single particles. Light scattering methods are proposed to improve the measuring procedure and statistical significance. The new methods, DR/phase analysis light scattering and ER/light scattering, are presented in detail in two additional manuscripts. (C) 1999 Elsevier Science B.V. All rights reserved.


  29. An ISFET-algal (Chlamydomonas) hybrid provides a system for eco-toxicological tests.
    Schubnell, D; Lehmann, M; Baumann, W; Rott, FG; Wolf, B; Beck, CF. 1999. BIOSENSORS & BIOELECTRONICS 14 (5): 465-472.

    30. Abstract: A cellular sensoring system was designed in which metabolism-dedicated pH-ISFETs and the unicellular green alga Chlamydomonas reinhardtii as a biological component, were combined. The system permits on-line detection of pH changes caused by the metabolic and photosynthetic activities of the cells. Photosynthetic activity results in a basification of the medium caused by uptake of CO2. In darkness, an acidification of the medium, resulting from the production of CO2 by degradation of starch was observed. Both, acidification and basification, are sensitive indicators for the physiological activity of the alga. Experiments using inhibitors of energy metabolism or photosynthesis illustrate the utility of this system for an on-line monitoring of substances of eco-toxicological importance.


  30. A unified resistor-capacitor model for impedance, dielectrophoresis, electrorotation, and induced transmembrane potential.
    Gimsa, J; Wachner, D. 1998. BIOPHYSICAL JOURNAL 75 (2): 1107-1116.

    31. Abstract: Dielectric properties of suspended cells are explored by analysis of the frequency-dependent response to electric fields. Impedance (IMP) registers the electric response, and kinetic phenomena like orientation, translation, deformation, or rotation can also be analyzed. All responses can generally be described by a unified theory. This is demonstrated by an RC model for the structural polarizations of biological cells, allowing intuitive comparison of the IMP, dielectrophoresis (DP), and electrorotation (ER) methods. For derivations, cells of prismatic geometry embedded in elementary cubes formed by the external solution were assumed. All geometrical constituents of the model were described by parallel circuits of a capacitor and a resistor. The IMP of the suspension is given by a meshwork of elementary cubes. Each elementary cube was modeled by two branches describing the current flow through and around the cell. To model DP and ER, the external branch was subdivided to obtain a reference potential. Real and imaginary parts of the potential difference of the cell surface and the reference reflect the frequency behavior of DP and ER, The scheme resembles an unbalanced Wheatstone bridge, in which IMP measures the current-voltage behavior of the feed signal and DP and ER are the measuring signal. Model predictions were consistent with IMP, DP, and ER experiments on human red cells, as well as with the frequency dependence of field-induced hemolysis, The influential radius concept is proposed, which allows easy derivation of simplified equations for the characteristic properties of a spherical single-shell model on the basis of the RC model.


  31. Particle characterization by AC-electrokinetic phenomena - 3. New developments in electrorotational light scattering (ERLS)
    Pruger, B; Eppmann, P; Gimsa, J. 1998. COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS 136 (1-2): 199-207.

    32. Abstract: Dielectric dispersions of the polarizability of suspended particles can be directly measured by electrorotation (ER). The method records particle rotation spectra in rotating electric fields of the radio frequency range. The frequency dependence of ER spectra is characterized by individual rotation peaks which provide information on inherent electric particle structures. To avoid the inconveniences of microscopic registration of particle rotation we developed electrorotational light scattering (ERLS). Results on human red blood cells, platelets and conducting latices are presented. For all particles the obtained ERLS spectra corresponded to microscopic measurements. New methodological developments such as the introduction of optical microstructured chambers are discussed. These chambers possess a simple structure and expand the available frequency and conductivity range. A special measuring procedure which distinguishes between the rotation sense at the measuring frequency relative to the sense at a reference frequency is presented. The procedure is also useful to reject the contributions of held-induced particle motions other than ER and to enhance the sensitivity of ERLS in frequency ranges of smaller particle rotations. (C) 1998 Elsevier Science B.V.


  32. Monitoring of cellular signalling and metabolism with modular sensor-technique. The PhysioControl-Microsystem (PCM®).
    Wolf, B; Brischwein, M; Baumann, W; Ehret, R; Kraus, M. 1998. BIOSENSORS & BIOELECTRONICS 13 (5): 501-509.

    33. Abstract: Microsensors provide instruments particularly suited for the noninvasive analysis of cell and tissue cultures. The outstanding benefit lies in the passive behaviour of continuously working transducers, which in turn allows the dynamic recording of function-specific cellular processes. The microsensor system presented in this paper is a modular arrangement of various planar and nonplanar sensor elements surrounding small cell culture chambers. An optic access to the cultures (e.g. for high resolution light microscopy and spectro-photometric techniques) enables a parallel and comparative data acquisition. The system was originally designed for biomedical research in chemotherapy and pharmacology but it proved to be an effective device both for toxicological and environmental research.


  33. Microsensor-aided measurements of cellular signalling and metabolism on tumor cells - The Cell Monitoring System (CMS®)
    Wolf, B; Brischwein, M; Baumann, W; Ehret, R; Henning, T; Lehmann, M; Schwinde, A. 1998. TUMOR BIOLOGY 19 (5): 374-383.

    34. Abstract: Microsensors provide instruments particularly suited for the rapid, noninvasive and on-line analysis of cell and tissue cultures. The microsensor system presented in this paper is a modular arrangement of various planar and nonplanar sensor elements for the measurement of physiological parameters of cell cultures. An optic access to the cultures (e.g. for light microscopy and spectrophotometric techniques) is also provided for a parallel and comparative data acquisition. The system was originally designed for biomedical research in chemotherapy (predicative chemotherapy assays) and pharmacology but it turned out to be also an effective tool for toxicological and environmental research.


  34. Biofunctional hybrid structures - cell-silicon hybrids for applications in biomedicine and bioinformatics
    Wolf, B; Kraus, M; Brischwein, M; Ehret, R; Baumann, W; Lehmann, M. 1998. BIOELECTROCHEMISTRY AND BIOENERGETICS 46 (2): 215-225.

    35. Abstract: Cell-silicon hybrids represent miniaturized analytical systems which are qualified by means of the cellular signal processing network to identify biomolecules and biophysical signals in a highly specific and quantitative manner. Such biofunctional hybrid structures are also appropriate tools for a number of experimental approaches where specific reaction patterns and signal transducing processes of living cells are tested in response to defined environmental stimuli. The paper describes how cellular systems can function as multi-potent signal discriminators and interfaces to a variety of physical detection arrays. The analysis is based on recent results regarding the understanding of the intracellular signal transduction network. Our systems analytical approach gives an idea how the biological component of a cellular biosensor works and facilitates the directed design of new families of biofunctional hybrid structures. After a brief review of the construction lines of cell-silicon hybrids, novel improvements of their design and their applicability in tumor biology will be discussed.


  35. Introducing phase analysis light scattering for dielectric characterization: Measurement of traveling-wave pumping.
    Gimsa, J; Eppmann, P; Pruger, B. 1997. BIOPHYSICAL JOURNAL 73 (6): 3309-3316.

    36. Abstract: Phase analysis light scattering (PALS) was applied to characterize a high-frequency traveling-wave (TW) micropump. Field strength and frequency characteristics were measured for aqueous solutions up to 40 MHz and conductivities of 16 mS/m. The TW field was generated by an ultramicroelectrode array of intercastellated electrodes, which were driven by square-topped signals. Pumping exhibited one major relaxation peak, which strongly increased for conductivities above 4 mS/m. The conductivity dependence of the peak frequency showed an unexpected nonlinear behavior. Around 20 MHz an additional peak caused by electronic resonance was found. Additional coils or capacitors shifted the resonance peak and alLowed us to determine the electronic properties of the array. Analysis of distortions in the pump spectra caused by the harmonic content of the driving signals showed that the pump direction is determined by the traveling direction of the field. For measurement of AC-field-induced particle translations, the advantage of PALS over the commonly used microscopic analysis is that it offers an objective method for statistically significant, computerized registration of extremely slow motions. Thus, for dielectric characterization, low field strengths can be used, which is advantageous not only for analyzing liquid pumping, but also for measuring particle translations induced by dielectrophoresis or TW dielectrophoresis.


  36. A resonant,dielectric micro-motor driven by low ac-voltages (<6V).
    Muller, T; Gimsa, J; Wagner, B; Fuhr, G. 1997. MICROSYSTEM TECHNOLOGIES 3 (4): 168-170.

    37. Abstract: An asynchronous, dielectric micro-motor consisting of an AL-SiO2 rotor of 50 to 200 mu m diameter was driven with 4 or 8 circularly arranged electrodes in water. The motor elements were fabricated by micromachining. Each electrode was designed to be an oscillatory circuit with a sharp resonance frequency in the upper kHz-range. The resonances at all electrode tips increase the voltage in the stater-rotor gap by a factor of up to 15. As a result, the dielectric rotor operates in a sharp frequency window at 5 V-pp excitation as if driven with more than 75 V-pp. With square wave pulses, the higher order Fourier-components induce several changes in rotor spin direction within two frequency decades. The micro-motor has been driven for hours without noticeable wear. It developed high starting torques and was useful for circular water pumping. The system has the advantage of very sensitive frequency dependence and the low drive voltages (below 10 V) can be produced by most electronic circuits.


  37. Determination of viral neuraminidase specificity for membrane-bound sialic acids by cell electrophoresis.
    Gimsa, U; Gimsa, J. 1997. MOLECULAR MEMBRANE BIOLOGY 14 (2): 87-90.

    38. Abstract: The ability of the influenza virus neuraminidase (NA) to cleave specific sialic acids was measured by cell electrophoresis. Most of the surface charge of human erythrocytes can be attributed to sialic acids. Therefore cleavage of sialic acids reduces the surface charge density which is measurable as a reduced cell electrophoretic mobility (EPM). For experiments specifically sialylated, erythrocytes were used. Their EPM was significantly decreased after incubation with Virus strains possessing the corresponding NA specificity, even when the viral haemagglutinin (HA) was unable to bind to the erythrocyte's surface. Thus, the limited applicability of elution experiments, which requires virus binding, is overcome. An additional advantage of this procedure is that it is non-radioactive. In our model system the erythrocyte's surface resembles the natural situation of viral interaction with membrane-bound receptors.


  38. Measurement of inherent particle properties by dynamic light scattering: Introducing electrorotational light scattering.
    Pruger, B; Eppmann, P; Donath, E; Gimsa, J. 1997. BIOPHYSICAL JOURNAL 72 (3): 1414-1424.

    39. Abstract: Common dynamic light scattering (DLS) methods determine the size and zeta-potential of particles by analyzing the motion resulting from thermal noise or electrophoretic force. Dielectric particle spectroscopy by common microscopic electrorotation (ER) measures the frequency dependence of field-induced rotation of single particles to analyze their inherent dielectric structure. We propose a new technique, electrorotational light scattering (ERLS), It measures ER in a particle ensemble by a homodyne DLS setup. ER-induced particle rotation is extracted from the initial decorrelation of the intensity autocorrelation function (ACF) by a simple optical particle model, Human red blood cells were used as test particles, and changes of the characteristic frequency of membrane dispersion induced by the ionophore nystatin were monitored by ERLS, For untreated control cells, a rotation frequency of 2 s(-1) was induced at the membrane peak frequency of 150 kHz and a field strength of 12 kV/m, This rotation led to a decorrelation of the ACF about 10 times steeper than that of the field free control, For deduction of ERLS frequency spectra, different criteria are discussed. Particle shape and additional field-induced motions like dielectrophoresis and particle-particle attraction do not significantly influence the criteria, For nystatin-treated cells, recalculation of dielectric cell properties revealed an ionophore-induced decrease in the internal conductivity. Although the absolute rotation speed and the rotation sense are not yet directly accessible, ERLS eliminates the tedious microscopic measurements. It offers computerized, statistically significant measurements of dielectric particle properties that are especially suitable for nonbiological applications, e.g., the study of colloidal particles.


  39. Handling and investigation of adherently growing cells and viruses, of medical relevance in three-dimensional micro-structures.
    Fuhr, G; Muller, T; Schnelle, Th; Glasser, H; Gimsa, J; Hofmann, U; Wagner, B. 1997. Micro Electro Mechanical Systems, 1997. MEMS '97, Proceedings, IEEE., Tenth Annual International Workshop on DOI:10.1109/MEMSYS.1997.581851.

    40. Abstract: The investigation of animal cells in microstructures fabricated by semiconductor technology is a new field of research and has found its first biotechnological and medical uses. This paper contains selected examples of three-dimensional structures to handle and characterise adherently growing cells, to determine their adhesion, surface migration and to cultivate them under strong electric field. Two new principles, (i) the use of electronic resonances to increase polarisation forces and (ii) the computer-based investigation of cell rotation/cell dielectrophoresis by photoelement signal analysis, are explained. Additionally, some results dealing with the trapping and concentration of submicron particles such as viruses in extremely miniaturised electric field cages are given. Perspectives for such semiconductor micro-devices are outlined


  40. Monitoring of cellular behaviour by impedance measurements on interdigitated electrode structures
    Ehret, R; Baumann, W; Brischwein, M; Schwinde, A; Stegbauer, K; Wolf, B. 1997. Biosensors & Bioelectronics 12 (1): 29-41.

    41. Abstract: A new method for on-line and real-time monitoring of concentration, growth and physiological state of cells in culture is described. This biosensor is based on impedance measurements of adherently growing cells on interdigitated electrode structures (IDES). The measurements can be performed for several days as there is no detectable electrical influence on the cells. The versatility of this new sensor is shown with some exemplary experiments. Cell density, growth and long-term behaviour of cells on the electrodes clearly change the impedance of the IDES. Both, the global influence of serum components (deprivation of foetal bovine serum) and the toxic effects of heavy metal ions (cadmium) result in changes of the sensor signal and can be visualized.


  41. Physiocontrol microsystems in cell biology research and medical diagnostics
    Brischwein, M; Baumann, W; Ehret, R; Schwinde, A; Kraus, M; Wolf, B. 1996. NATURWISSENSCHAFTEN 83 (5): 193-200.

    42. Abstract: The development of an integrated sensor system, called the physiocontrol microsystem, is presented. It is suited for microscopy, and works with both adherent cell types and cultures growing in suspension, as well as with tissue biopsies. The central part, a miniaturized culture chamber equipped with differently constructed microsensors, allows continuous observation of important physiological parameters even in the course of long-lasting experiments. Besides a description of the physical components, the study provides a summary of selected applications of the physio-control microsystem in basic cellular research and biomedical diagnostics.


  42. Two evolutionary strategies of influenza viruses to escape host non-specific inhibitors: Alteration of hemagglutinin or neuraminidase specificity.
    Gimsa, U; Grotzinger, I; Gimsa, J. 1996. VIRUS RESEARCH 42 (1-2): 127-135.

    43. Abstract: The porcine serum inhibitor alpha(2)-macroglobulin prevents influenza virus from entering host cells by competing for the SA alpha 2,6Gal-binding site of the hemagglutinin (HA). We studied a series of inhibitor-sensitive and inhibitor-resistant human and porcine influenza virus isolates of the H3N2 subtype, all of which contained HAs, which initially bound only to SA alpha 2,6Gal oligosaccharides. When their neuraminidase was inhibited, the naturally resistant viruses, as a result of no longer being able to elute from the inhibitor, became sensitive. Evidently it is the neuraminidase which enabled these viruses to grow in hosts which possess the inhibitor. Escape-mutants selected under laboratory conditions in the presence of porcine serum became inhibitor-resistant by two alternative mechanisms: they changed either their HA-specificity or their neuraminidase-specificity. The study thus disclosed two evolutionary strategies for acquiring resistance to a host neuraminidase-sensitive inhibitor: (i) acquisition of an HA able to bind to oligosaccharides not present on the inhibitor; or (ii) acquisition of a neuraminidase able to cleave the oligosaccharide bound by the HA.


  43. Dielectric spectroscopy of single human erythrocytes at physiological ionic strength: Dispersion of the cytoplasm.
    Gimsa, J; Muller, T; Schnelle, T; Fuhr, G. 1996. BIOPHYSICAL JOURNAL 71 (1): 495-506.

    44. Abstract: Usually dielectrophoretic and electrorotation measurements are carried out at low ionic strength to reduce electrolysis and heat production. Such problems are minimized in microelectrode chambers. In a planar ultramicroelectrode chamber fabricated by semiconductor technology, we were able to measure the dielectric properties of human red blood cells in the frequency range from 2 kHz to 200 MHz up to physiological ion concentrations. At low ionic strength, red cells exhibit a typical electrorotation spectrum with an antifield rotation peak at low frequencies and a cofield rotation peak at higher ones. With increasing medium conductivity, both electrorotational peaks shift toward higher frequencies. The cofield peak becomes antifield for conductivities higher than 0.5 S/m. Because the polarizability of the external medium at these ionic strengths becomes similar to that of the cytoplasm, properties can be measured more sensitively. The critical dielectrophoretic frequencies were also determined. From our measurements, in the wide conductivity range from 2 mS/m to 1.5 S/m we propose a single-shell erythrocyte model. This pictures the cell as an oblate spheroid with a long semiaxis of 3.3 mu m and an axial ratio of 1:2. Its membrane exhibits a capacitance of 0.997 x 10(-2) F/m(2) and a specific conductance of 480 S/m(2). The cytoplasmic parameters, a conductivity of 0.4 S/m at a dielectric constant of 212, disperse around 15 MHz to become 0.535 S/m and 50, respectively. We attribute this cytoplasmic dispersion to hemoglobin and cytoplasmic ion properties. In electrorotation measurements at about 60 MHz, an unexpectedly low rotation speed was observed. Around 180 MHz, the speed increased dramatically. By analysis of the electric chamber circuit properties, we were able to show that these effects are not due to cell polarization but are instead caused by a dramatic increase in the chamber field strength around 180 MHz. Although the chamber exhibits a resonance around 180 MHz, the harmonic content of the square-topped driving signals generates distortions of electrorotational spectra at far Lower frequencies. Possible technological applications of chamber resonances are mentioned.


  44. Dynamic light scattering from oriented, rotating particles: A theoretical study and comparison to electrorotation data.
    Eppmann, P; Gimsa, J; Pruger, B; Donath, E. 1996. JOURNAL DE PHYSIQUE III 6 (3): 421-432.

    45. Abstract: In recent years, electrorotation has developed in the held of biology as a technique for characterization of single cell dielectric properties. Applications to colloidal particles are scarce, although the method provides information on the electrical structure of the particle's interior. The method explores the frequency-dependent polarizability difference of the particles and the suspension medium by using rotating fields in the frequency range of 1 kHz to 200 MHz to induce individual particle rotation. To allow interpretation of the electrorotation spectra measured with light scattering techniques, the theoretical autocorrelation function of light scattered from rotating particles of cylindrical symmetry has been calculated. All particles were assumed to possess a single scattering site and the rotation axes were assumed to be parallel. An appropriate expression for the rotational diffusion around the longitudinal angle was also derived. Diffusion around the azimuthal angle could be neglected. The theoretical result consists of a well structured autocorrelation function. The theoretical limits of particle size and rotation speed that allow detection of electrorotation were explored. Experimental autocorrelation functions from electrorotation of human red blood cells could be explained theoretically when reasonable parameters for the cells' properties were assumed.


  45. Do band-3 protein conformational-changes mediate shape changes of human erythrocytes ?
    Gimsa, J; Ried, C. 1995. MOLECULAR MEMBRANE BIOLOGY 12 (3): 247-254.

    46. Abstract: The bilayer-couple model predicts a reversible membrane crenation for an increasing ratio of external to internal monolayer area. This was comprehensively proven. However, individual erythrocytes may undergo dramatic shape changes within seconds when the suspension medium is changed. In contrast, under physiological conditions with no addition of membrane active compounds, active phospholipid translocation and passive flip-flops are comparatively slow. We propose that conformational changes of the anion-exchange protein, band 3, may rapidly alter the monolayer area ratio. Band 3 occupies about 10% of the total membrane area of human erythrocytes. Under physiological conditions, its conformers are asymmetrically distributed with about 90% of the transport sites facing the cytoplasm. This distribution is altered when external conformations are recruited by changing the transmembranous CI- gradient, the external pH, or by the application of inhibitors. In experiments, recruitment by low ionic strength caused a rapid, temporary formation of echinocytes. This suspension effect could also be found at high ionic concentrations, when CI- was replaced by SO42-. Inhibitors known to recruit 4 the external band 3 conformation, like DIDS, SITS and flufenamic acid, are echinocytogenic. For inhibitors not recruiting a certain conformation, e.g. phenylglyoxal and niflumic acid, no shape effect was found. Since band 3 ensures a fast equilibrium of internal and external anions these ions are usually distributed according to the transmembrane potential (TMP). In the literature, a correlation of TMP and band 3 conformation, as well as a correlation of TMP and red cell shape, is described. in the proposed model, low external CI- concentrations, inhibitors, or a negative TMP may recruit the transport sit outwards. This increases the bulk of the protein in the external monolayer and, subsequently, leads to the formation of echinocytes.


  46. Red-cell echinocytogenesis is correlated to the recruitment of external band-3 conformations.
    Gimsa, J. 1995. BIOELECTROCHEMISTRY AND BIOENERGETICS 38 (1): 99-103.

    47. Abstract: For human erythrocytes the bilayer-couple model predicts a reversible crenation for increasing ratios of external to internal membrane monolayer area. This can be proven experimentally by changing the ratio of lipids in the two monolayers. Under physiological conditions with no addition of membrane-active compounds, active lipid translocation and passive flip-flop are comparatively slow. Nevertheless, individual erythrocytes underwent dramatic shape changes within seconds when the suspension medium was changed. After cell suspension in low ionic strength solutions a rapid formation of echinocytes was observed. This suspension effect was also found at high ionic concentrations when Cl- was replaced by SO42-, an ion transported very slowly by band 3. The band-3 anion-exchange protein occupies about 10% of the total membrane area. Band-3 conformers are asymmetrically distributed with about 90% of the transport sites facing the inside. Specific band-3 inhibitors can induce echinocytes. These inhibitors are known to recruit the band-3 conformation with he transport site exposed to the external medium, e.g. 4,4'-diisothio-cyanatostilbene-2,2'-disulfonic acid, 4-acet-amido-4'-isothiocyana-tostilbene-2,2'-disulfonic acid, flufenamic acid, furosemide and salicylic acid. Other inhibitors, e.g. phenylglyoxal and niflumic acid, which do not recruit a certain conformation, are not echinocytogenic. Physiologically, band 3 ensures the equilibration of internal and external anions like Cl- and HCO3- which are distributed according to the transmembrane potential (TMP). In the literature a correlation of the TMP and the band-3 conformation, as well as a correlation of the TMP and the erythrocyte shape, is described. In the proposed model, conformational changes may significantly alter the monolayer area ratio. Low external Cl- concentrations, negative TMPs or inhibitors may recruit the band-3 transport site towards the outside solution. It is proposed that this increases the bulk of the protein in the external monolayer and subsequently induces an echinocytogenic shape transformation according to the bilayer couple model.


  47. Electrorotation of particles measured by dynamic light-scattering - a new dielectric-spectroscopy technique.
    Gimsa, J; Pruger, B; Eppmann, P; Donath, E. 1995. Colloids and surfaces a-physicochemical and engineering aspects 98 (3): 243-249.

    48. Abstract: Electrorotation provides information about the dielectric and conductive properties of particles over a large frequency range, which is not easily available from other techniques. Numerous applications of the dielectric particle spectroscopy technique have already been demonstrated by microscopic measurements in the held of biology. Aware of the serious limitations of microscopy for applications in colloid science, we demonstrate that dynamic light scattering can be used to measure electrorotation spectra. A suitable chamber was designed which fits into a commercial correlation spectrometer. Measurements on human red blood cells showed that the apparent diameter of the particles recorded as a function of the frequency of the rotating field matches the microscopically measured electrorotation spectrum. However, the applicability of conventional dynamic light scattering sizing-devices to the recording of electrorotation spectra is limited, since the autocorrelation function in the presence of particle rotation is a superposition of zero-order Bessel functions. Consequently, new mathematical techniques have to be developed. Another limitation is that the direction of rotation is not yet detectable. Nevertheless, since the new method overcomes the restrictions of microscopic observations it offers a potentially wide range of applications for colloidal particles, vesicles, microemulsions, subcellular particles, and cells.


  48. Dielectric-spectroscopy of human erythrocytes - investigations under the influence of nystatin.
    Gimsa, J; Schnelle, T; Zechel, G; Glaser, R. 1994. BIOPHYSICAL JOURNAL 66 (4): 1244-1253.

    49. Abstract: When placed in rotating electric fields red blood cells show a typical electrorotation spectrum with antifield rotation in the Lower and cofield rotation in the higher frequency range. Assuming a spherical cell geometry, however, dielectrical parameters were obtained that differ from those measured by independent methods. Dielectrophoresis and, in particular, electrorotation yielded Lower membrane capacitance values than expected. Introduction of an ellipsoidal model with an axis ratio of 1:2 alLowed a description that proved to be consistent with dielectrophoresis and electrorotation data. For control cells an internal conductivity of 0.535 S/m, a specific membrane capacitance of 0.82 x 10(-2) F/m(2), and a specific conductance of 480 S/m(2) were obtained. The first characteristic frequency (frequency of fastest antifield rotation) and the related rotation speed can be measured quite quickly by means of a compensation method. Thus it was possible to follow changes of dielectric properties on individual cells after nystatin application. lonophore-membrane interaction caused cell shrinkage in parallel to a decrease of the first characteristic frequency and rotation speed. Analysis of data revealed a decrease of the internal conductivity that is not only caused by ion loss but also, to a large extent, by a strong increase of hindrance because of shrinkage. Ionophore-induced membrane permeabilities can be calculated from volume decrease as well as from electrorotational data. In no case can these permeabilities count for the high membrane-AC conductivity that is attributed to the band-3 anion exchanging protein. The membrane-AC conductance was found not to be decreased for cells in Donnan equilibrium, which had leaked out almost completely.


  49. Electroporation in rotating electric-fields.
    Gimsa, J; Marszalek, P; Loewe, U; Tsong, TY. 1992. BIOELECTROCHEMISTRY AND BIOENERGETICS 29 (1): 81-89.

    50. Abstract: The entrance of the fluorescence dye, propidium iodide, into murine myeloma cells after poration of the cytoplasmic membrane by application of a rotating electric field for 100 ms was monitored, The dye becomes strongly fluorescent only when bound to cellular DNA. The poration field was generated between four electrodes driven by four 90-degrees-phase-shifted square-wave signals. Field strength and frequency were about 80 kV/m and 2.5 kHz respectively. After membrane permeabilization by the rotating field pulse, the dye entered through the electropores giving rise to intense fluorescence, initially only in the vicinity of the porated membrane areas. Different types of fluorescence pattern for the cytoplasm were found after the pulse. Spherical cells showed either a ring-shaped fluorescence increase or an increase starting at one or more points. For elongated cells the increase always occurred at membrane points close to the two ends of the long axis. These experiments show the advantage of rotating fields for biotechnological applications. More gentle field conditions can be used because these fields scan the cell surface. Scanning increases the probability of poration of randomly oriented non-spherical cells or of the weakest membrane points of electrically inhomogeneous cells.


  50. Analysis of the torque frequency-characteristics of dielectric induction-motors.
    Fuhr, GR; Hagedorn, R; Gimsa, J. 1992. SENSORS AND ACTUATORS A-PHYSICAL 33 (3): 237-247.

    51. Abstract: The torque produced by a dielectric induction motor (IM) is a complex function of the system geometry, dielectric architecture of the rotor, field strength and frequency. This paper gives an overview about the analysis of the steady-state operation of rotors of complex architecture based on published and original calculations. Derivations of the frequency-rotation and torque-frequency characteristics of different types of dielectric rotors are summarized. Important aspects of the dielectric relaxation principle and differences from electrostatic synchronous motors are discussed. The presented theoretical framework allows the torque of a large number of complex rotors driven by rectangular field pulses or sinusoidal excitation to be calculated. For experiments, micromotors are fabricated with conventional techniques, having rotors with diameters from 3-mu-m down to 3 mm. The characteristic parameters of these motors are found to be in good agreement with our theoretical predictions. Recent advances in micromachining technology give the possibility of fabricating an IM using silicon technology. Relations to this technique are briefly discussed.


  51. Ion channel enzyme in an oscillating electric-field.
    Markin, VS; Liu, DS; Gimsa, J; Strobel, R; Rosenberg, MD; Tsong, TY. 1992. JOURNAL OF MEMBRANE BIOLOGY 126 (2): 137-145.

    52. Abstract: To explain the electrical activation of several membrane ATPases, an electroconformational coupling (ECC) model has previously been proposed. The model explained many features of experimental data but failed to reproduce a window of the field intensity for the stimulated activity. It is shown here that if the affinities of the ion for the two conformational states of the transporter (one with binding site on the left side and the other on the right side of the membrane) are dependent on the electric field, the field-dependent transport can exhibit the observed window. The transporter may be described as a channel enzyme which opens to one side of the membrane at a time. It retains the energy-transducing ability of the earlier ECC models. Analysis of the channel enzyme in terms of the Michaelis-Menten kinetics has been done. The model reproduced the amplitude window for the electric field-induced cation pumping by (Na,K)-ATPase.


  52. Traveling-wave dielectrophoresis of microparticles.
    Hagedorn, R; Fuhr, G; Muller, T; Gimsa, J. 1992. ELECTROPHORESIS 13 (1-2): 49-54.

    53. Abstract: The traveling-wave-induced linear transfer of dielectric particles like living cells and artificial objects of microscopic dimensions is analyzed. It is shown that the electrode geometries must correspond to particle sizes to allow an effective manipulation of particles immersed in weakly electrolytic solutions by high frequency traveling waves. The theoretical model elaborated in this paper is in good agreement with experimental results obtained in microfabricated chambers of linearly arranged electrodes. It explains the behavior of homogeneous cellulose spheres as well as that of membrane-covered pine polls. The traveling-wave-driven electrodes are described by a superposition of time-dependent point charges. Subsequently, each of these point charges has to be considered as polarizing the dielectric particle and interacting with the polarized particle. This results in forces which effectively translocate the particle.


  53. Asynchronous traveling-wave induced linear motion of living cells.
    Fuhr, G; Hagedorn, R; Muller, T; Benecke, W; Wagner, B; Gimsa, J. 1991. STUDIA BIOPHYSICA 140 (2): 79-102.

    54. Abstract: An electrodynamic traveling-wave induced linear transfer of dielectric particles such as living cells and artificial objects of microscopic dimensions is described. Various configurations of microelectrodes obtained by microfabrication techniques were realized on silicon or glass substrates. For an effective manipulation of particles immersed in weak electrolyte solutions (i) electrode geometries corresponding with particle size and (ii) high frequency traveling-waves have to be used. The motion of particles can be characterized as traveling-wave dielectrophoresis (TWD). Microparticle velocities of some hundred mu-m/s have been achieved applying phase-shifted rectangular pulses with amplitudes between 4 and 15 volts. A theoretical estimation of the particle motion is given.


  54. Dielectrophoresis and electrorotation of neurospora slime and murine myeloma cells.
    Gimsa, J; Marszalek, P; Loewe, U; Tsong, TY. 1991. BIOPHYSICAL JOURNAL 60 (4): 749-760.

    55. Abstract: Dielectrophoresis and electrorotation are commonly used to measure dielectric properties and membrane electrical parameters of biological cells. We have derived quantitative relationships for several critical points, defined in Fig. A 1, which characterize the dielectrophoretic spectrum and the electrorotational spectrum of a cell, based on the single-shell model (Pauly, H., and H.P. Schwan. 1959. Z. Naturforsch. 14b:125-131; Sauer, F.A. 1985. Interactions between Electromagnetic Field and Cells. A. Chiabrera, C. Nicolini, and H.P. Schwan, editors. Plenum Publishing Corp., New York. 181-202). To test these equations and to obtain membrane electrical parameters, a technique which alLowed simultaneous measurements of the dielectrophoresis and the electrorotation of single cells in the same chamber, was developed and applied to the study of Neurospora slime and the Myeloma Tib9 cell line. Membrane electrical parameters were determined by the dependence of the first critical frequency of dielectrophoresis (f(ct1)) and the first characteristic frequency of electrorotation (f(c1)) on the conductivity of the suspending medium. Membrane conductances of Neurospora slime and Myeloma also were found to be 500 and 380 S m-2, respectively. Several observations indicate that these cells are more complex than that described by the single-shell model. First, the membrane capacities from f(ct1) (0.81 x 10(-2) and 1.55 x 10(-2) F m-2 for neurospora slime and Myeloma, respectively) were at least twice those derived from f(c1). Second, the electrorotation spectrum of Myeloma cells deviated from the single-shell like behavior. These discrepancies could be eliminated by adapting a three-shell model (Furhr, G., J. Gimsa, and R. Glaser. 1985. Stud. Biophys. 108:149-164). Apparently, there was more than one membrane relaxation process which could influence the Lower frequency region of the beta-dispersion. f(ct1) of Myeloma in a medium of given external conductivity were found to be similar for most cells, but for some a dramatically increased f(ct1) was recorded. Model analysis suggested that a decrease in the cytoplasmatic conductivity due to a drastic ion loss in a cell could cause this increase in f(ct1). Model analysis also suggested that the electrorotation spectrum in the counter-field rotation range and f(c1) would be more sensitive to conductivity changes of the cytoplasmic fluid and to the influence of internal membranes than would f(ct1), although the latter would be sensitive to changes in capacitance of the cytoplasmic membranes.


  55. Electric activation of membrane atpases by electroconformational coupling.
    Liu, DS; Gimsa, J; Markin, VS; Rosenberg, MD; Tsong, TY. 1991. FASEB JOURNAL 5 (5): A1151-A1151, Part 2.

  56. AC-field-induced KCl leakage from human red-cells at low ionic strengths - implications for electrorotation measurements.
    Georgiewa, R; Donath, E; Gimsa, J; Lowe, U; Glaser, R. 1989. BIOELECTROCHEMISTRY AND BIOENERGETICS 22 (3): 255-270.

    57. Abstract: It is shown that the field strengths used in electrorotation measurements are capable of stimulating an ionic efflux at low ionic strength. This efflux decreases the internal conductivity of human erythrocytes drastically within a few minutes. Even in the initial phase of the field's influence, the field-induced efflux is clearly stronger than the one induced by low ionic strengths. The field-induced efflux correlates with the frequency dependency of the electrorotation. The efflux decreases with increasing frequency, particularly in the range of the first characteristic frequency. From this fact one can draw the conclusion that the field induces a membrane permeabilization. DIDS inhibits more than 60% of both the efflux at low ionic strengths and the additional field-induced efflux, which makes at least a partial participation of band 3 in the process of membrane permeabilization in ac electric fields more likely.


  57. Characterization of virus-red-cell interaction by electrorotation.
    Gimsa, J; Pritzen, C; Donath, E. 1989. STUDIA BIOPHYSICA 130 (1-3): 123-131.

    58. Abstract: Virus-membrane fusion induced by a temperature increase from 4°C to 37°C caused a characteristic time dependence of the first characteristic frequency and of the rotation. An initial increase of the first characteristic frequency was followed by a decrease well below the value of the control. Rotation decreased in a characteristic manner, too. This process was terminated by hemolysis about 10 minutes after induction of fusion. The electrorotation changes were explained by a sequence of ion permeability changes.


  58. Evaluation of the data of simple cells by electrorotation using square-topped fields.
    Gimsa, J; Donath, E; Glaser, R. 1988. BIOELECTROCHEMISTRY AND BIOENERGETICS 19 (3): 389-396.

    59. Abstract: In electrorotation digital generators of rotating electric fields producing various pulse shapes are used widely. The available theory however, allows only for monochromatic fields. It is shown how to recalculate experimental data in order to apply the theory of electrorotation. As an example, square-topped fields are analyzed. The result is that in square-topped fields the electrorotation spectrum is shifted as a function of the key ratio. Furthermore, in order to eliminate the uncertainty of not knowing precisely hydrodynamic friction of the particle under consideration, a special numerical procedure was introduced. It compared the slope of the experimental curve near the zero point of rotation with the heights of the rotation peaks.


  59. Electrorotation of red-cells after electroporation.
    Engel, J; Donath, E; Gimsa, J. 1988. STUDIA BIOPHYSICA 125 (1): 53-62.

  60. Remarks on the field distribution in 4 electrode chambers for electrorotational measurements.
    Gimsa, J; Glaser, R; Fuhr, G. 1988. STUDIA BIOPHYSICA 125 (1): 71-76.

    61. Abstract: By means of electrorotation the dielectric properties of cells or other dielectric particles can be investigated. To measure electrorotation usually four-electrode-chambers are employed. Field distribution in these chambers were studied. Recommendations of electrode shapes for electrorotational measurements are made. The special case of only one driven electrode for dielectrophoretic measurements or for adjusting cells in the chamber was considered too.


  61. Membrane-potentials induced by external rotating electrical fields.
    Fuhr, G; Hagedorn, R; Glaser, R; Gimsa, J; Muller, T. 1987. JOURNAL OF BIOELECTRICITY 6 (1): 49-69.

    62. Abstract: For electrorotation measurements of cell properties, cells are positioned in a rotating electric field, generated by a System of four electrodes. The membrane potentiale induced by such fields were calculated for single-, two-, and three-shell models. This simulates the Situation of cells like erythrocytes that contain a single membrane System, protoplasts with a vacuole, or plant cells covered by a cell' wall. The influence of the outside field on cell organelles was also calculated. Differentes between alternating and rotating fields are discussed. A measuring chamber was developed which allowed the production of rotating fields up to 40 kV/m. The effects of such fields an the rotational behavior of plant protoplasts (Kalanchoe daigremontiana, Avena sativa) are discussed. Dielectric breakdown of protoplasts induced by rotating fields is investigated to check the theoretical predictions.


  62. Electrorotation - capabilities and limitations.
    Glaser, R; Fuhr, G; Gimsa, J; Hagedorn, R. 1985. STUDIA BIOPHYSICA 110 (1-3): 43-50.

  63. Interpretation of electrorotation of protoplasts. 2. Interpretation of experiments.
    Gimsa, J; Fuhr, G; Glaser, R. 1985. STUDIA BIOPHYSICA 109 (1): 5-14.

    64. Abstract: This paper deals with the electrorotational behaviour of protoplasts. It is related to the theoretical discussion in /5/. Protoplasts of different species (Avena sativa, Brassica oleracea, Kalanchoe daigremontiana, Daucus carota, and Solanum tuberosum) were investigated. There is evidence that both membrane systems, tonoplast and plasmalemma, respectively, influence the protoplast rotation spectrum in the range of the first resonance frequency. Types of protoplasts were classified, using theoretical and experimental date. Emphasis is put on the necessity to consider the electrorotational spectra of protoplasts as those of multi-shell spheres.


  64. Interpretation of electrorotation of protoplasts. 1. Theoretical considerations.
    Fuhr, G; Gimsa, J; Glaser, R. 1985. STUDIA BIOPHYSICA 108 (3): 149-164.

    65. Abstract: This paper contains the theoretical fundament of the rotation of protoplasts in high-frequency rotating electric fields (electrorotation). The protoplasts have to be calculated as three-shell spheres, considering their composition of vacuole, tonoplast, cell plasma, and plasmalemma. In contrast to the behaviour of single-shell bodies, the electrorotation spectrum indicates a rather complicated shape, depending an the dielectric properties of their compounds. This is demonstrated an theoretical rotation spectra which are calculated for typical parameters of protoplasts.


  65. Rotation of erythrocytes, plant-cells, and protoplasts in an outside rotating electric-field.
    Glaser, R; Fuhr, G; Gimsa, J. 1983. STUDIA BIOPHYSICA 96 (1): 11-20.

    66. Abstract: According to the method published by Arnold and Zimmermann 1982 human erythrocytes, suspension cultured cells of Beta vulgaris, protoplasts and isolated vacuoles were investigated. The cells rotate in the rotating electric field of a four electrode system. The rotation, defined as the torque per square field strength seems to be independent of the cellular diameter. The frequency for maximal rotation allows us to calculate specific membrane capacity or an effective capacity of plant cells sourrounded by cell wall, resp. This method also provides a sensitive measure of changes in membrane resistance since ionophores incorporated into the membrane innibit the torque in a reversible manner.