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Human red blood cells suspended in a slightly hypotonic solution of low electric conductivity were exposed to an inhomogeneous and alternating electric field (sine wave, 30 V peak-to-peak value, electrode distance 120 μm, 0.5 to 2 MHz). Due to the dielectrophoretic effect the cells align parallel to the field lines under the formation of pearl chains. At high voltages (10 V amplitude) membrane fusion is observed between the adhered red blood cells in the pearl chains, whereby the chains become attached to the electrodes. In contrast to the pearl chains observed at voltages of up to 5 V amplitude the resulting fused and uniform aggregates which exhibit no recognisable individual cells under the light microscope, remain stable, even after the alternating electric field has been switched off or after haemolysis in response to osmotic shock. The fused aggregates are highly elastic. If the field strength of the applied alternating electric field is further increased they are stretched in the direction of the opposite electrode. Frequently, bridges are formed between the two electrodes. The uniform bridges remain stable for some time even in the absence of an electric field. The possibility of cell fusion and its initiation by electrical breakdown of the cell membranes are discussed.

Rotation of "lone" cells of the baker's yeast Saccharomyces cerevisiae under the influence of nonuniform alternating fields is studied.The spinning rate of the ceils shows a quadratic dependence on the applied voltage and no threshold effect when the influence of gravitation is cancelled out by adjusting the density of the buffer to that of the cells. These observations are in agreement with theories established by different authors.Among the various effects that nonuniform alternating electric fields exhibit on biological material, rotation is one of the most interesting. It was described by several authors for different organisms such as amoebae (Teixeira-Pinto, et al., 1960), erythrocytes (Fiiredi and Ohad, 1964) and yeasts (Pohl and Crane, 1971). Rotation seemed to be a quite general phenomenon of living and dead cells or inanimate materials that could be observed in a broad range of frequencies. As this effect is closely related to dielectrophoresis (DEP;Pohl, 1978) and to the effective dielectric constant of the particle in the surrounding medium, it may offer an elegant method to determine this parameter and to investigate the physical state of biological material.Although rotating fields were mentioned briefly (Pohl and Crane, 1971), they were only recently employed to investigate the spinning of single cells (Arnold and Zimmermann, 1982a, 1982b;Mischel, et al., 1982;Mischel and Pohl, 1983). Also recently, theories were developed to explain the occurrence of rotation in cells in the neighborhood of other ones (Holzapfel et al., 1982) and in single cells .Pohl and Crane (1971) used the description term "cellular spin resonance" (CSR) for this phenomenon, because the spinning of cells appears at a sharply resonant frequency of the external field. If highly homogeneous cell cultures are used nearly all cells spin in the same small frequency interval (Zimmermann et al., 1981). Nevertheless, it is possible to find spinning cells at all applied frequencies, mainly in direct contact with the electrodes.Although rotation of cells was described long ago, to our knowledge Mischel and Lamprecht (1980) were the first to give qumltitative data about spinning rates and their connections with some physical and biologic parameters. These first experiments were performed in a DEP chamber which consisted of a microslide with a central well of 1.0 mm, into which two electrodes dipped at an angle of about 10 ~ . The electrodes were produced from a platinum plate 0.5 mm thick with carefully rounded and polished tops. The minimum distance between the electrodes amounted to 2 mm. The height of the electrode tips above the floor of the well measured 0.3 mm or 35 cell diameters.A new type of DEP chamber used in recent experiments consisted of a microslide to which two similar platinum electrodes (0.2 mm thick) were glued with epoxy resin with a minimum separation of 0.2 mm or 0.5 mm, resp. Much care was taken in smoothing and polishing the electrode surface and the edges. The surface quality was so high that the refl...

Lipid membrane Ion distribution Neutron diffraction