Deregulation by zinc of the sodium efflux in barnacle muscle fibers.
Single muscle fibers from the barnacle Balanus nubilus were employed to study the behavior of the resting Na+ efflux toward external and internal application of zinc (Zn2+). This involved both unpoisoned and ouabain-poisoned fibers. The results obtained are as follows: (i) External application of Zn2+, e.g., 2 mM (a maximal dosage) in 10 mM Hepes-ASW (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 application of Zn2+ is concentration-dependent, the IC50 being 10 microM. (iv) The inhibitory effect of Zn2+ is partially reversible; occasionally, however, reversibility is not seen. (v) The Zn(2+)-insensitive component of the Na+ efflux is reduced by 10(-4) M ouabain. (vi) The ouabain-insensitive component of the Na+ efflux is reduced by external application of Zn2+. This response is concentration-dependent. (vii) Preinjection of EGTA reduces the sensitivity of the Na+ efflux to external application of Zn2+. This is true of both unpoisoned and ouabain-poisoned fibers. (viii) (a) The resting Na+ efflux is reduced by injecting Zn2+. Ouabain application reduces the remaining Na+ efflux. (b) Injection of Zn2+ reduces the ouabain-insensitive component of the Na+ efflux. (c) External 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 without effect. Subsequent application of ouabain is also without effect. (e) Injection or external application of Zn2+ reduces the ouabain-insensitive Na+ efflux. Whereas in the former case subsequent external application of Zn2+ reduces the remaining Na+ efflux, in the latter case Zn2+ injection after external application of Zn2+ is ineffective. Collectively, 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 effect is partly due to the entry of Zn2+ into the myoplasm. They also raise the possibility that the inhibitory effect caused by Zn2+ injection may be the result of Zn2+ leakage from the fiber interior.
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Department of Physiology, University of Wisconsin, Madison 53706.
Bittar
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D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D001468:Thoracica; D013997:Time Factors; D015032:Zinc / Q000494:pharmacology*
D010042:Ouabain; D012964:Sodium; D015032:Zinc