Kleyman T R, Ernst S A, Coupaye-Gerard B
Department of Medicine, University of Pennsylvania.
Am J Physiol. 1994 Mar;266(3 Pt 2):F506-11. doi: 10.1152/ajprenal.1994.266.3.F506.
Both arginine vasopressin (AVP) and forskolin regulate vectorial Na+ transport across high-resistance epithelia by increasing the Na+ conductance of the apical membrane mediated by amiloride-sensitive Na+ channels. Pretreatment of A6 cells with brefeldin A partially inhibited the increase in Na+ transport in response to forskolin, suggesting recruitment of Na+ channels from an intracellular pool. The activation of Cl- secretion was not affected. Apical cell surface expression of Na+ channels was examined following activation of transepithelial Na+ transport across the epithelial cell line A6 by AVP or forskolin. Apical cell surface radioiodinated Na+ channels were immunoprecipitated to quantify the biochemical pool of Na+ channels at the apical plasma membrane and to determine whether an increment in the biochemical pool of Na+ channels expressed at the apical cell surface is a potential mechanism by which AVP and forskolin increase apical membrane Na+ conductance. The activation of Na+ transport across A6 cells by AVP was accompanied by a significant increase in the biochemical pool of Na+ channels at the apical plasma membrane within 5 min after addition of hormone, which was sustained for at least 30 min. The increase in apical cell surface expression of Na+ channels was also observed 30 min after application of forskolin. No changes in the oligomeric subunit composition of the channel were noted. Brefeldin A inhibited the forskolin-stimulated increase in apical cell surface expression of Na+ channels. These results suggest that AVP and forskolin regulate Na+ transport, in part, via rapid recruitment of Na+ channels to the cell surface, perhaps from a pool of channels in the subapical cytoplasm.
精氨酸加压素（AVP）和福斯高林都通过增加由氨氯地平敏感的钠离子通道介导的顶端膜的钠离子电导率，来调节跨高电阻上皮细胞的向量钠离子转运。用布雷菲德菌素A预处理A6细胞可部分抑制福斯高林刺激引起的钠离子转运增加，提示从细胞内池募集钠离子通道。氯离子分泌的激活不受影响。在用AVP或福斯高林激活跨上皮细胞系A6的跨上皮钠离子转运后，检测顶端细胞表面钠离子通道的表达。对顶端细胞表面放射性碘化的钠离子通道进行免疫沉淀，以定量顶端质膜上钠离子通道的生化池，并确定顶端细胞表面表达的钠离子通道生化池的增加是否是AVP和福斯高林增加顶端膜钠离子电导率的潜在机制。在添加激素后5分钟内，AVP激活A6细胞的钠离子转运伴随着顶端质膜上钠离子通道生化池的显著增加，这种增加持续至少30分钟。在应用福斯高林30分钟后，也观察到顶端细胞表面钠离子通道表达增加。未观察到通道寡聚亚基组成的变化。布雷菲德菌素A抑制福斯高林刺激引起的顶端细胞表面钠离子通道表达增加。这些结果表明，AVP和福斯高林部分通过将钠离子通道快速募集到细胞表面来调节钠离子转运，可能是从顶端下细胞质中的通道池中募集。
