The ability and inability of ATP to stop aluminum from reducing the sodium efflux in unpoisoned barnacle muscle fibers.

A study has been made in single barnacle muscle fibers with the object of determining whether ATP is able to protect the resting Na efflux from the effects of injected aluminum (Al) and whether Al is able to reduce or abolish the stimulatory action of ATP on the efflux. The results of the experiments show that neither ATPMg nor ATPNa2 preinjection stops Al from reducing the basal Na efflux in unpoisoned fibers which undergo a large fall (hypersensitive fibers). Preinjection of Al into such fibers reduces or abolishes the stimulatory response of the Na efflux to ATP injection. In less hypersensitive fibers, however, ATPMg is protective. This is also true of ATPNa2 preinjection in both classes of fibers showing stimulation. Injection of a mixture of AlCl3-ATPNa2 into unpoisoned fibers causes less inhibition than AlCl3 injection. The hypothesis that both ATPMg and ATPNa2 are protective is also supported by the results obtained with ouabain-poisoned fibers: (i) Al injection after ATP fails to reverse the stimulatory response to ATP, while ATP injection after Al exerts only a small or no effect. (ii) Mg2+ injection fails to reverse the stimulatory response to Al injection in poisoned fibers. And (iii) Anti-proteolysis agents e.g. leupeptin and pepstatin, upon preinjection, do not alter the kinetic results obtained by injecting Al into unpoisoned and ouabain-poisoned fibers.