A dielectric theory of interfacial polarization is presented for a heterogeneous system containing ellipsoidal particles covered with shells, in order to make an analysis of dielectric behavior of suspensions of ellipsoidal biological cells. For the case of spheroidal shapes, dielectric dispersion curves are calculated numerically by using the electrical and morphological parameters relevant to biological cells. The results indicate that the calculated dielectric dispersion curves are seriously affected by varying the axial ratio of the spheroids. For the purpose of analyzing dielectric data of biological cell suspensions on the basis of the presented theory, a procedure is proposed to evaluate electrical parameters characteristic of biological cells. This procedure is shown to be successfully applied to the observed dielectric data of erythrocyte suspensions.

Dielectric measurements of Escherichia coli suspensions were carried out over a frequency range from 10 kHz to 100 MHz, and marked dielectric dispersions having characteristic frequency of approximately 1 MHz were observed. On the basis of the cell model that a spheroid is covered with two confocal shells, a dielectric theory was developed to determine accurately four electrical parameters for E. coli cells such as the conductivity of the cell wall, the dielectric constant of the cell membrane, and the dielectric constant and the conductivity of the protoplasm. The observed data were analyzed by means of the procedure based on the dielectric theory to yield a set of plausible electrical parameters for the cells. By taking account of the size distribution of the cells and a dielectric relaxation of the protoplasm, the observed dispersion curves were successfully reconstituted by the present theory.

Dielectric measurements were made on suspensions of intact yeast cells over a frequency range of 10kHz to 100 MHz. The suspensions showed typical dielectric dispersions, which are considered to be caused by the presence of cytoplasmic membranes with sufficiently low conductivity. Since the conductivity of the cell wall was found to be of nearly the same value as that of the suspending medium, composed of Kcl solutions in a range from 10 to 80 mM, the cell wall may be ignored in establishing an electrical model of the cells suspended in such media. An analysis of the dielectric data was carried out by use of Pauly and Schwan's theory. The membrane capacitance was estimated to be 1.1+/-0.1 muF/cm2, which is compared with values reported so far for most biological membranes. The conductivity of the cell interior was almost unchanged with varying KCl concentrations and showed low values owing to the presence of less conducting particles, presumably intracellular organelles. The relatively low dielectric constant of about 50 obtained for the cell interior, in comparison with values of aqueous solutions, may be attributed also to the presence of intracellular organelles and proteins.

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