ELECTROROTATION OF SINGLE YEAST-CELLS AT FREQUENCIES BETWEEN 100 HZ AND 1.6 GHZ

The determination of complete electrorotation spectra of living cells has been made possible by the development of a quadrature generator an d an electrode assembly that span the frequency range between 100 Hz a nd 1.6 GHz. Multiple spectra of single cells of the yeast Saccharomyce s cerevisiae have been measured at different medium conductivities ran ging from 0.7 to 550 mu S cm(-1). A spherical four-shell model was app lied that simulated the experimental data well and disclosed the four- layer structure of the cell envelope attributed to the plasma membrane , the periplasmic space, and a thick inner and a thin outer wall regio n, Below 10 kHz an additional rotation effect was found, which changed its direction depending on the ionic strength of the medium. This is supposed to be connected with properties of the cell surface and its c lose vicinity. From the four-shell simulation the following physical p roperties of cell compartments could be derived: specific capacitance of plasma membrane (0.76 mu F cm(-2)), periplasmic space (0.5 mu F cm( -2)), and outer wall region (0.1 mu F cm(-2)). The conductivity of cyt oplasm, plasma membrane, and inner wall region were found to vary with medium ionic strength from 9 to 12 mS cm(-1), 5.8 nS cm(-1) to simila r to 50 nS cm(-1), and 6 mu S cm(-1) to 240 mu S cm-l, respectively.