Fisher R S, Lockard J W
Department of Nephrology, Walter Reed Army Institute of Research, Washington, DC 20307-5100.
Am J Physiol. 1988 Feb;254(2 Pt 1):C297-303. doi: 10.1152/ajpcell.1988.254.2.C297.
When toad urinary bladder or frog skin epithelia are treated with amiloride, short-circuit current (Isc), which represents the net active transepithelial Na+ transport rate from the apical to basolateral surface, decreases rapidly (2-5 s) to approximately 15-20% of control values and then slowly, over several minutes, continues falling toward zero. The contribution of this second phase of the decline is dependent on the transporting condition of the tissue before administration of amiloride. Attenuation of the second phase was observed if tissues were subjected to a period of transport inhibition. Tissues preincubated in 0 Na+ Ringer solution on the apical surface were returned to control Na+ Ringer, which caused an approximately 25% increase of Isc above control values. Immediate reapplication of amiloride caused Isc to decrease more rapidly than the previous exposure to values near zero, substantially reducing or eliminating the secondary slow decline. After long-term reincubation of tissues in control, 100 mM Na+ solution, another treatment with amiloride indicated that the magnitude of the secondary decline increased in frog skin but not in urinary bladder epithelia. We conclude that the effect of amiloride is complex and may cause additional effects besides simply blocking entry of Na+ into the apical membrane channel, and we suggest that regulatory mechanisms may be invoked in response to transport inhibition.
当用氨氯吡咪处理蟾蜍膀胱或青蛙皮肤上皮时，代表从顶端到基底外侧表面的净主动跨上皮Na⁺转运速率的短路电流（Isc）迅速（2 - 5秒）降至对照值的约15 - 20%，然后在几分钟内缓慢持续下降至零。下降的第二阶段的程度取决于给药前组织的转运状态。如果组织经历一段时间的转运抑制，则观察到第二阶段的衰减。在顶端表面用0 Na⁺林格溶液预孵育的组织恢复到对照Na⁺林格溶液，这导致Isc比对照值增加约25%。立即重新应用氨氯吡咪导致Isc比先前暴露时更快地下降至接近零的值，大大减少或消除了继发性缓慢下降。在对照的100 mM Na⁺溶液中对组织进行长期再孵育后，另一次用氨氯吡咪处理表明，继发性下降的幅度在青蛙皮肤中增加，但在膀胱上皮中没有增加。我们得出结论，氨氯吡咪的作用是复杂的，除了简单地阻断Na⁺进入顶端膜通道外，可能还会引起其他影响，并且我们认为可能会调用调节机制来响应转运抑制。
