外部Cd2+和Ca2+离子对蛙皮（非洲爪蟾）钠转运的一种新型协同刺激作用。

A novel synergistic stimulation of Na+-transport across frog skin (Xenopus laevis) by external Cd2+- and Ca2+-ions.

作者信息

Scholtz E, Zeiske W

机构信息

Institut für Tierphysiologie und angewandte Zoologie, Freie Universität Berlin, Federal Republic of Germany.

出版信息

Pflugers Arch. 1988 Dec;413(2):174-80. doi: 10.1007/BF00582528.

DOI:10.1007/BF00582528

PMID:3217238

Abstract

Isolated skin of the clawed frog Xenopus laevis was mounted in an Ussing-chamber. The transcellular sodium-current (INa) was identified either as amiloride-blockable (10(-3) mol/l) short-circuit current (ISC), or by correcting ISC for the shunt-current obtained with mucosal Tris. A dose of 10 mmol/l Cd2+ applied to the mucosal side increased the current by about 70%. The half-maximal effect was reached at a Cd2+-concentration of 2.6 mmol/l (in NaCl-Ringer). The quick and fully reversible effect of Cd2+ could not be seen when 10(-3) mol/l amiloride was placed in the outer, Na+-containing solution, nor when Na+ was replaced by Tris. This suggests that Cd2+ stimulates INa. Cd2+ interfered with the Na+-current self-inhibition, and therefore with the saturation of INa by increasing the apparent Michaelis constant (KNa) of this process. The "INa recline" after stepping up mucosal [Na+] was much reduced in presence of Cd2+. Ca2+-ions on the mucosal side had an identical effect to Cd2+, and 10 mmol/l Ca2+ increase INa by about 100%. The half-maximal effect was obtained with 4.4 mmol/l Ca2+. The mechanism of INa-stimulation by Ca2+ did not seem to differ from that of Cd2+. Thus, although of low Na+-transport capacity, Xenopus skin appears to be as good a model for Na+-transporting epithelia as Ranidae skin, with the exception of the calcium effect which, so far, has not been reported for Ranidae.

摘要

将非洲爪蟾（Xenopus laevis）的离体皮肤置于尤斯灌流小室中。跨细胞钠电流（INa）可通过两种方式确定：一是可被氨氯吡脒阻断（10⁻³ mol/L）的短路电流（ISC），二是通过用黏膜侧的 Tris 校正 ISC 来确定。向黏膜侧施加 10 mmol/L 的 Cd²⁺ 可使电流增加约 70%。在 Cd²⁺ 浓度为 2.6 mmol/L（在 NaCl - 林格氏液中）时达到半数最大效应。当在含 Na⁺ 的外部溶液中加入 10⁻³ mol/L 的氨氯吡脒时，或者当 Na⁺ 被 Tris 取代时，看不到 Cd²⁺ 的快速且完全可逆的效应。这表明 Cd²⁺ 刺激 INa。Cd²⁺ 干扰了钠电流的自身抑制，因此通过增加该过程的表观米氏常数（KNa）来干扰 INa 的饱和。在 Cd²⁺ 存在的情况下，黏膜侧 [Na⁺] 升高后的“INa 斜降”大大减少。黏膜侧的 Ca²⁺ 离子对 INa 的作用与 Cd²⁺ 相同，10 mmol/L 的 Ca²⁺ 可使 INa 增加约 100%。在 Ca²⁺ 浓度为 4.4 mmol/L 时达到半数最大效应。Ca²⁺ 刺激 INa 的机制似乎与 Cd²⁺ 的机制没有差异。因此，尽管非洲爪蟾皮肤的钠转运能力较低，但除了蛙科皮肤尚未报道的钙效应外，它似乎是与蛙科皮肤一样好的钠转运上皮模型。