Ca2+-activated K+ current generating the after-hyperpolarization in mammalian nonmyelinated nerve fibres.

Abstract

Results and discussion The results showed that the amplitude of the a.h.p. increased with decreasing the external concentration of potassium. The maximal amplitude was obtained in absence of K+ o, whereas at physiological concentration (5.6 mM) there remained only a slight rapid a.h.p. followed by a slower transient after-depolarization (a.d.p.). A further increase in K+ o produced an almost complete abolition of the a.h.p, and an even more pronounced a.d.p. Fig. 1 shows that both a.h.p, and a.d.p, are clearly Ca2+o-dependent. At physiological (5.6 mM) and lower than physiological concentrations of K+o (1.4 mM), the amplitude of the a.h.p, increased with increasing external Ca 2+. Decreasing Ca2+ o decreased the a.h.p, but a complete abolition of the a.h.p, by Ca2+-free solution was never obtained. In high K+o (11.2 mM), where the after-potential is composed of mainly the depolarizing component, the a.d.p, increased with increasing Ca2+ o, and was completely absent when Ca2+o was withdrawn. The Ca2+-sensitivity of the after-potential was further tested by blocking the voltage-sensitive Ca 2+ channels