Anode break excitation on single Ranvier node of frog nerve

Abstract

A quantitative study of anodal break excitation in single frog nerve fibers has been carried out. An applied anodal pulse caused an increase in the critical level of depolarization for excitation. Anode break stimulation was effective only if the anodal pulse was immediately followed by depolarization of the single Ranvier node membrane. This condition can be obtained in three ways: 1) by applying the anodal pulse during a conditioning depolarization voltage, which must be equal to or greater than the threshold value for cathodal stimulation; 2) by applying a pulse of such large amplitude so as to produce membrane breakdown, which results in depolarization by intrinsic local currents; 3) by applying the pulse to a fiber already under the influence of intrinsic depolarization resulting from deterioration or high concentrations of potassium in the external solution. True anode break stimulation can only be produced by an exceedingly strong positive pulse. The membrane breakdown resulting from such a pulse, first reported by Stampfli in 1958, is discussed and a hypothesis is presented explaining the physiological implications of this phenomena.