Activation of Electrogenic Na+ Pump by Epinephrine in Bullfrog Atrium

Abstract

The effects of epinephrine [Ep] (1 .times. 10-6-1 .times. 10-5 M) on the resting membrane potential and the K+-activated hyperpolarization of bullfrog [Rana catesbeiana] atrial heart muscles were studied by the single sucrose-gap method or by intracellular microelectrode filled with 3 M KCl. Ep-induced hyperpolarization was completely eliminated by the effect of ouabain or by removal of extracellular K+. The amplitude of K+-activated hyperpolarization, which was produced when the extracellular K+ concentration was raised from 0 to 2 mM, was markedly increased in the presence of Ep. The membrane depolarizations, due to high extracellular K+ concentration in the presence of ouabain (5 .times. 10-6 M) which completely and reversibly eliminated the K+-activated hyperpolarization, were not altered under the effect of Ep. Ep-hyperpolarization of bullfrog atrial heart muscles was due to the acceleration of electrogenic Na+ pump which produced the K+-activated hyperpolarization.