Kinetics of slow changes in membrane potential induced by direct current polarization of single nerve fibers.

Abstract

A direct current pulse applied to an isolated single fiber of the frog sciatic induces a slow drift in membrane potential which can be described by a single exponential term throughout most of its time course. Both magnitude and time parameter are functions of pre-existent membrane potential. With increasing cathodal polarization the magnitude of the drift approaches a limiting value which is dependent only on the duration of the polarizing pulse. No change in resistance is detectable with brief test transient pulses. In fibers sufficiently hyperpolarized to minimize sodium inactivation it is observed that impulses fired off at any time during the course of the slow potential drift are characterized by identical peak values of membrane potential. This indicates that active firing results in a short circuiting of the mechanism responsible for the slow drift. Whereas the data presented favor a change in some e.m.f. as responsible for the slow drift, there exists strong evidence that the potassium emf remains constant.