Toxin‐Induced K+ Efflux through the Na+ Channel of Neuroblastoma Cells

Abstract

Neurotoxins which modify the gating system of the Na+ channel in neuroblastoma cells and increase the initial rate of 22Na+ influx through this channel also give rise to the efflux of 86Rb+ and 42K+. These effluxes are inhibited by tetrodotoxin and are dependent on the presence in the extracellular medium of cations permeable to the Na+ channel. These stimulated effluxes are not due to membrane depolarization or increases in the intracellular content of Na+ and Ca2+ which occur subsequent to the action of neurotoxins. The relationships of 22Na+ influx and 42K+ (or 86Rb+) effluxes to the concentration of neurotoxins and the concentration of external permeant cations strongly suggest that the open form of the Na+ channel stabilized by neurotoxins permits an efflux of K+ ions. For the efflux of each K+ ion there apparently is a corresponding influx of 2 Na+ ions into the Na+ channel.