Modification of single Na+ channels by batrachotoxin.

Abstract

The modifications in the properties of voltage-gated Na+ channels caused by batrachotoxin [isolated from frog skin] were studied by using the patch clamp method for measuring single channel currents from excised membranes of mouse N1E-115 neuroblastoma cells. The toxin-modified open state of the Na+ channel has a decreased conductance in comparison to that of normal Na+ channels. The life-time of the modified open state is drastically prolonged, and channels now continue to open during a maintained depolarization so that the probability of a channel being open becomes constant. Modified and normal open states of Na+ channels coexist in batrachotoxin-exposed membrane patches. Unlike the normal condition, Na+ channels exposed to batrachotoxin open spontaneously at large negative potentials. These spontaneous openings apparently cause the toxin-induced increase in Na+ permeability which in turn causes membrane depolarization.