DEREGULATION BY ZINC OF THE SODIUM-EFFLUX IN BARNACLE MUSCLE-FIBERS

Single muscle fibers from the barnacle Balanus nubilus were employed t o study the behavior of the resting Na+ efflux toward external and int ernal application of zinc (Zn2+). This involved both unpoisoned and ou abain-poisoned fibers. The results obtained are as follows: (i) Extern al application of Zn2+, e.g., 2 mM (a maximal dosage) in 10 mM Hepes-A SW (pH 7.3) causes a fall in the resting Na+ efflux which exceeds that caused by 10(-4) M ouabain in companion controls. (ii) The buffer of choice is found to be Hepes, rather than HCO3- or imidazole. (iii) The observed fall in the resting Na+ efflux caused by external applicatio n of Zn2+ is concentration-dependent, the IC50 being 10 mu M. (iv) The inhibitory effect of Zn2+ is partially reversible; occasionally, howe ver, reversibility is not seen. (v) The Zn2+-insensitive component of the Na+ efflux is reduced by 10(-4) M ouabain. (vi) The ouabain-insens itive component of the Na+ efflux is reduced by external application o f Zn2+. This response is concentration-dependent. (vii) Preinjection o f EGTA reduces the sensitivity of the Na+ efflux to external applicati on of Zn2+. This is true of both unpoisoned and ouabain-poisoned fiber s. (viii) (a) The resting Na+ efflux is reduced by injecting Zn2+. Oua bain application reduces the remaining Na+ efflux. (b) Injection of Zn 2+ reduces the ouabain-insensitive component of the Na+ efflux. (c) Ex ternal application of Zn2+ following the injection of Zn2+ reduces the remaining Na+ efflux. Ouabain is ineffective when applied after both maneuvers. (d) Injection of Zn2+ after its external application is wit hout effect. Subsequent application of ouabain is also without effect. (e) Injection or external application of Zn2+ reduces the ouabain-ins ensitive Na+ efflux. Whereas in the former case subsequent external ap plication of Zn2+ reduces the remaining Na+ efflux, in the latter case Zn2+ injection after external application of Zn2+ is ineffective. Col lectively, these results provide evidence in support of the hypothesis that Zn2+ is a potent inhibitor of the ouabain-sensitive and ouabain- insensitive components of the Na+ efflux, and that the inhibitory effe ct is partly due to the entry of Zn2+ into the myoplasm. They also rai se the possibility that the inhibitory effect caused by Zn2+ injection may be the result of Zn2+ leakage from the fiber interior.