Mechanisms responsible for electrical properties of tissues and cell suspensions

The electrical properties of tissues and cell suspensions are most unusual. They change with frequency in three distinct steps and their dielectric constants reach enormous values at low frequencies. We shall concentrate on the 'linear' properties as observed with applied fields less than 1 V/cm. The linear properties of interest include the dielectric constant epsilon and conductivity kappa. Extensive measurements have been carried out over a broad frequency range extending from less than 1 Hz to many GHz. Observed frequency changes of these properties obey causality, i.e., the Kramers-Kronig relationships which relate changes of dielectric constants with conductivity changes. A number of mechanisms have been identified which explain the observed data. These mechanisms reflect the various compartments of the biological material. These include membranes and their properties, biological macromolecules and fluid compartments inside and outside membranes. We summarize the mechanisms which contribute to the total frequency response.