Frequency response of alternating currents through the Staphylococcus aureus alpha-hemolysin ion channel.

Alternating currents were measured through transmembrane ion channels formed by Staphylococcus aureus alpha-hemolysin proteins in planar bilayer membranes as part of an investigation to determine the channel's frequency response and the appropriateness of an equivalent circuit commonly used to model electrical interactions at the surface of cells. The experimental approach includes a novel method for separating the alternating current through one or more channels, which is conductive in nature, from the capacitively coupled current through the membrane. Separation of the conductive and capacitive alternating currents made it possible to measure the frequency response of the alpha-hemolysin channels. The results of the study are consistent with an equivalent circuit of a membrane capacitor in parallel with one or more channel resistors over the frequency range 30-120 Hz. The possible usefulness of frequency response data for ion channels in cell membranes during investigations of biological effects of time-varying magnetic fields is briefly discussed.