Tohsak L. Mahaworasilpa, Hans G. L. Coster and Eric P. George
UNESCO Centre for Membrane Science and Technology, Department of Biophysics, School of Physics, University of New South Wales, N.S.W. Sydney, Australia 2052
Electro-rotation of the cells was observed when two cells are in contact between two parallel, cylindrical electrodes to which AC signals are applied. Measurements are presented of angular velocities of rotation of mammalian cells of K562 (human) and SP2 (mouse) in external alternating electric fields over a frequency range of 0.5 kHz to 12 MHz . A theoretical analysis was made which shows that the cell rotation arises from a torque produced by the interaction between the primary electric dipole moment induced in the spinning cell and the secondary electric fields generated by the primary dipole induced in the adjacent cell. These secondary fields are out of phase with the applied electric field. The results show that (a) the electro-rotation occurs at two different excitation field frequency domains for the frequency range employed here, (b) the spin speed of the rotating cell at each frequency domain is much less than the excitation frequency, (c) the rotation direction of the cell depends on the angle (q) between the external electric field and the line joining the centres of the two cells and (d) for a given angle q, the rotation direction is the same for both excitation frequency domains. The experimental measurements allowed us to estimate the conductivities of the cytoplasms and membrane capacitances of the cells of K562 and SP2. The conductivities of the cytoplasm of the cells of K562 and SP2 were estimated to be 0.2 and 0.3 S.m-1, respectively, whereas the membrane capacitances of these cells were found to be 2.7 + 0.8 and 9.8 + 0.6 mF.m-2, respectively.