Impedance of a Small Electrically Isolated Area of the Muscle Cell Surface.

A method has been developed permitting measurement of membrane impedance and current, as a function of transmembrane potential, at small, electrically isolated regions of the muscle cell surface without microelectrode impalement. The frequency dependence of the muscle cell membrane capacity found earlier by other methods has been confirmed. The average capacity is 3.5 microf/cm(2) with a phase angle of 71 degrees at 5 kilocycles. The internal phase angle of the complex impedance plot of whole muscle probably does not result from a distribution of fiber diameters and membrane capacities, since it also appears in the present experiments where measurements are confined to a small region of a single fiber.