Further studies of the mechanism of stimulation by external acidification of the sodium efflux in barnacle muscle fibers.

Abstract

1. The efflux of sodium in ouabain-poisoned barnacle muscle fibers is markedly stimulated by injecting ATPNa2 but not by ATPMg. This response is partly or completely reversed by injecting the protein inhibitor of Walsh. Injection of EGTA following ATPNa2 partially reverses the stimulatory response; EGTA followed by protein inhibitor completely reverse together the response but only temporarily. Preinjection of EGTA enhances the response to an injection of ATPNa2. The enhanced response is almost completely reversed by an injection of protein inhibitor. 2. Stimulation of the ouabain-insensitive Na efflux by acidification is completely reversed by injecting the protein inhibitor. It is also almost completely reversed following injection of 1–2 M-solutions of KHCO3. However, injection of KHCO3 fails to modify the response produced by injecting ATPNa2 or the partial reversal produced by injecting protein inhibitor. 3. Benzolamide (5×10−4 M) almost completely abolishes the stimulation caused by external acidification. Its action is dose-dependent, 38% inhibition being observed with a 10−7 M-solution.