Xie H, Bittar E E
Department of Physiology, University of Wisconsin, Madison 53706.
Biochim Biophys Acta. 1993 Dec 12;1153(2):219-24. doi: 10.1016/0005-2736(93)90408-r.
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.
利用藤壶（Balanus nubilus）的单根肌纤维来研究静息状态下钠外流对细胞外和细胞内施加锌（Zn2+）的反应。这涉及未中毒和哇巴因中毒的纤维。得到的结果如下：（i）在10 mM Hepes -人工海水（pH 7.3）中细胞外施加Zn2+，例如2 mM（最大剂量），会导致静息钠外流下降，其下降幅度超过在对照中10(-4) M哇巴因所引起的下降幅度。（ii）发现首选的缓冲液是Hepes，而不是HCO3-或咪唑。（iii）观察到细胞外施加Zn2+所引起的静息钠外流下降是浓度依赖性的，IC50为10 microM。（iv）Zn2+的抑制作用部分可逆；然而，偶尔也看不到可逆性。（v）钠外流中对Zn2+不敏感的成分会被10(-4) M哇巴因降低。（vi）钠外流中对哇巴因不敏感的成分会因细胞外施加Zn2+而降低。这种反应是浓度依赖性的。（vii）预先注射乙二醇双乙胺醚四乙酸（EGTA）会降低钠外流对细胞外施加Zn2+的敏感性。未中毒和哇巴因中毒的纤维都是如此。（viii）（a）注射Zn2+会降低静息钠外流。施加哇巴因会降低剩余的钠外流。（b）注射Zn2+会降低钠外流中对哇巴因不敏感的成分。（c）在注射Zn2+后细胞外施加Zn2+会降低剩余的钠外流。在两种操作之后施加哇巴因则无效。（d）在细胞外施加Zn2+之后注射Zn2+没有效果。随后施加哇巴因也没有效果。（e）注射或细胞外施加Zn2+会降低对哇巴因不敏感的钠外流。在前一种情况下，随后细胞外施加Zn2+会降低剩余的钠外流，而在后一种情况下，在细胞外施加Zn2+之后注射Zn2+则无效。总体而言，这些结果为以下假说提供了证据支持：Zn2+是钠外流中对哇巴因敏感和对哇巴因不敏感成分的有效抑制剂，并且抑制作用部分是由于Zn2+进入肌浆所致。它们还提出了一种可能性，即注射Zn2+所引起的抑制作用可能是Zn2+从纤维内部泄漏的结果。
