美西螈胆囊上皮基底外侧[Na⁺]的电生理效应

Electrophysiological effects of basolateral [Na+] in Necturus gallbladder epithelium.

作者信息

Altenberg G A, Stoddard J S, Reuss L

机构信息

Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550.

出版信息

J Gen Physiol. 1992 Feb;99(2):241-62. doi: 10.1085/jgp.99.2.241.

DOI:10.1085/jgp.99.2.241

PMID:1613485

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC2216613/

Abstract

In Necturus gallbladder epithelium, lowering serosal [Na+] ([Na+]s) reversibly hyperpolarized the basolateral cell membrane voltage (Vcs) and reduced the fractional resistance of the apical membrane (fRa). Previous results have suggested that there is no sizable basolateral Na+ conductance and that there are apical Ca(2+)-activated K+ channels. Here, we studied the mechanisms of the electrophysiological effects of lowering [Na+]s, in particular the possibility that an elevation in intracellular free [Ca2+] hyperpolarizes Vcs by increasing gK+. When [Na+]s was reduced from 100.5 to 10.5 mM (tetramethylammonium substitution), Vcs hyperpolarized from -68 +/- 2 to a peak value of -82 +/- 2 mV (P less than 0.001), and fRa decreased from 0.84 +/- 0.02 to 0.62 +/- 0.02 (P less than 0.001). Addition of 5 mM tetraethylammonium (TEA+) to the mucosal solution reduced both the hyperpolarization of Vcs and the change in fRa, whereas serosal addition of TEA+ had no effect. Ouabain (10(-4) M, serosal side) produced a small depolarization of Vcs and reduced the hyperpolarization upon lowering [Na+]s, without affecting the decrease in fRa. The effects of mucosal TEA+ and serosal ouabain were additive. Neither amiloride (10(-5) or 10(-3) M) nor tetrodotoxin (10(-6) M) had any effects on Vcs or fRa or on their responses to lowering [Na+]s, suggesting that basolateral Na+ channels do not contribute to the control membrane voltage or to the hyperpolarization upon lowering [Na+]s. The basolateral membrane depolarization upon elevating [K+]s was increased transiently during the hyperpolarization of Vcs upon lowering [Na+]s. Since cable analysis experiments show that basolateral membrane resistance increased, a decrease in basolateral Cl- conductance (gCl-) is the main cause of the increased K+ selectivity. Lowering [Na+]s increases intracellular free [Ca2+], which may be responsible for the increase in the apical membrane TEA(+)-sensitive gK+. We conclude that the decrease in fRa by lowering [Na+]s is mainly caused by an increase in intracellular free [Ca2+], which activates TEA(+)-sensitive maxi K+ channels at the apical membrane and decreases apical membrane resistance. The hyperpolarization of Vcs is due to increase in: (a) apical membrane gK+, (b) the contribution of the Na+ pump to Vcs, (c) basolateral membrane K+ selectivity (decreased gCl-), and (d) intraepithelial current flow brought about by a paracellular diffusion potential.

摘要

在泥螈胆囊上皮中，降低浆膜面[Na⁺]（[Na⁺]s）可使基底外侧细胞膜电压（Vcs）可逆性超极化，并降低顶端膜的分数电阻（fRa）。先前的结果表明，不存在可观的基底外侧Na⁺电导，且存在顶端Ca²⁺激活的K⁺通道。在此，我们研究了降低[Na⁺]s产生电生理效应的机制，特别是细胞内游离[Ca²⁺]升高通过增加gK⁺使Vcs超极化的可能性。当[Na⁺]s从100.5 mM降至10.5 mM（四甲基铵替代）时，Vcs从-68±2 mV超极化至峰值-82±2 mV（P<0.001），fRa从0.84±0.02降至0.62±0.02（P<0.001）。向黏膜溶液中添加5 mM四乙铵（TEA⁺）可降低Vcs的超极化以及fRa的变化，而在浆膜面添加TEA⁺则无作用。哇巴因（10⁻⁴ M，浆膜侧）使Vcs产生小的去极化，并降低降低[Na⁺]s时的超极化，而不影响fRa的降低。黏膜TEA⁺和浆膜哇巴因的作用是相加的。阿米洛利（10⁻⁵或10⁻³ M）和河豚毒素（10⁻⁶ M）对Vcs或fRa或它们对降低[Na⁺]s的反应均无影响，这表明基底外侧Na⁺通道对控制膜电压或降低[Na⁺]s时的超极化无作用。在降低[Na⁺]s使Vcs超极化期间，升高[K⁺]s时基底外侧膜去极化会短暂增加。由于电缆分析实验表明基底外侧膜电阻增加，基底外侧Cl⁻电导（gCl⁻）降低是K⁺选择性增加的主要原因。降低[Na⁺]s会增加细胞内游离[Ca²⁺]，这可能是顶端膜对TEA⁺敏感的gK⁺增加的原因。我们得出结论，降低[Na⁺]s导致fRa降低主要是由于细胞内游离[Ca²⁺]增加，其激活顶端膜上对TEA⁺敏感的大电导K⁺通道并降低顶端膜电阻。Vcs的超极化是由于以下因素增加：（a）顶端膜gK⁺，（b）Na⁺泵对Vcs的贡献，（c）基底外侧膜K⁺选择性（gCl⁻降低），以及（d）由细胞旁扩散电位引起的上皮内电流流动。