Concerning stimulation by injected fluoroaluminate of the sodium efflux in barnacle muscle fibers

Abstract

Single barnacle muscle fibers from Balanus nubilus were used primarily to examine the validity of two ideas: first, that the injection of KF stimulates the ouabain-insensitive Na + efflux, and that this action is potentiated by adding AlCl 3 (Al) in a low concentration to the solution of KF prior to injection. And second, that the injection of a KF-AlCl 3 solution into ouabain-poisoned, K ±- depolarized fibers elicits a stimulatory response resembling that obtained by injecting GTP. The results of this study are as follows: injection of 0.5 M KF into unpoisoned fibers causes a sustained rise in the resting Na + efflux. However, injection of a 0.5 M KF, 10 −3 M AlCl 3 solution leads to a reduced rather than an augmented response. Whereas injection of 0.5 M KF into ouabain-poisoned fibers elicits a marked stimulatory response, the injection of 0.5 M KF, 10 −3 M AlCl 3 reduces the remaining Na + efflux. Injection of KF-AlCl 3 in equimolar concentrations, e.g., 0.25 M, elicits a response that is significantly larger than that obtained by injecting 0.25 M KF. A dose-response curve indicates that a 0.2 M solution of fluoroaluminate probably represents an optimal concentration. Injection of 0.3 M KF following peak stimulation by injecting 0.3 M AlCl 3 completely reverses this response to Al. In sharp contrast, injection of a 0.3 M KF, 0.3 M AlCl 3 mixture following peak stimulation by injecting 0.3 M AlCl 3 is ineffective. Injection of KF into ouabain-poisoned, K + depolarized fibers does not always cause sustained stimulation of the remaining Na + efflux. But injection of KF-AlCl 3 in equimolar concentration always seems to cause a delayed sustained stimulatory response. Sustained stimulation is also observed after injecting Na 2GTP. Although these results provide evidence in support of the hypothesis that the primary point of action of equimolar KF-AlCl 3 solutions following injection into barnacle fibers is the membrane adenylate cyclase system, they raise doubts about the validity of the concept that trace amounts of Al are required for KF to act as a positive effector of this system.