Electrorotation of single yeast cells at frequencies between 100 Hz and 1.6 GHz

Abstract

The determination of complete electrorotation spectra of living cells has been made possible by the development of a quadrature generator and an electrode assembly that span the frequency range between 100 Hz and 1.6 GHz. Multiple spectra of single cells of the yeast Saccharomyces cerevisiae have been measured at different medium conductivities ranging from 0.7 to 550 microS cm-1. A spherical four-shell model was applied 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 region. 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 close vicinity. From the four-shell simulation the following physical properties of cell compartments could be derived: specific capacitance of plasma membrane (0.76 microF cm-2), periplasmic space (0.5 microF cm-2), and outer wall region (0.1 microF cm-2). The conductivity of cytoplasm, 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 approximately 50 nS cm-1, and 6 microS cm-1 to 240 microS cm-1, respectively.