Transmembrane voltage induced by applied electric fields

Abstract

An exposure of a biological cell to an electric field results in the induced transmembrane voltage (ITV) proportional to the strength of the electric field and superimposed onto the resting transmembrane voltage for the duration of the exposure. The ITV can have a range of effects from modification of the activity of voltage-gated channels to membrane electroporation, and accurate knowledge of spatial distribution and time course of the ITV is important both for the studies of these phenomena and for effectiveness of their applications. Unlike the resting component of the transmembrane voltage, the induced component varies with position on the membrane, it depends on the shape of the cell and its orientation with respect to the electric field, and in dense cell suspensions and tissues also on the volume fraction occupied by the cells. Inducement of the ITV is a process characterized by a time constant, which amounts to tenths of a microsecond under physiological conditions. As a consequence, the time course of the ITV lags the time course of the electric field that induces it, and for exposures to alternating fields with frequencies above 1 MHz or to pulses with durations below 1 μs, the amplitude of the ITV induced by the field of a given amplitude starts to decrease with further increase of the field frequency or with further decrease of the pulse duration. With field frequencies approaching the GHz range or with pulse durations in the ns range, this attenuation of the ITV comes to a halt, and the voltages induced on the organelle membranes inside the cell can reach the same order of magnitude as the voltage induced by the same field on the plasma membrane, and under certain conditions even exceed it. After the description of methods for analytical derivation and numerical computation of the ITV, the main techniques for experimental determination of ITV are also outlined.