Li M, McCann J D, Welsh M J
Howard Hughes Medical Institute, Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242.
Am J Physiol. 1990 Aug;259(2 Pt 1):C295-301. doi: 10.1152/ajpcell.1990.259.2.C295.
Previous work has investigated the anion selectivity of transepithelial Cl- secretion by airway epithelia and its inhibition by the Cl(-)-channel blocker 5-nitro-2-(3-phenylpropylamino)benzoate (NPPB). Here we report the anion selectivity of the apical membrane and of the outwardly rectifying Cl- channel and the effect of NPPB on the Cl- channel. The anion selectivity sequence of the apical membrane determined with conventional microelectrodes in the native epithelium was SCN- greater than I- greater than Br- greater than NO3- approximately Cl- much greater than SO(4)2- approximately gluconate-. This contrasts with the observation that Cl- and Br- support transepithelial secretion but that I- does not. Thus the anion selectivity of transepithelial transport is determined by the basolateral membrane Cl- entry step. The anion selectivity of the outwardly rectifying Cl- channel studied in excised patches was the same as that of the apical membrane. We also found that NPPB reversibly blocked the outwardly rectifying Cl- channel from both the internal and external surfaces of the patch. NPPB, 10 microM, completely blocked the channel; lower concentrations caused a decrease in the probability of finding the channel in the open state. NPPB also caused the appearance of a subconductance state of the channel, an occurrence which is rarely observed in the absence of NPPB. These data provide further support for the conclusion that the outwardly rectifying Cl- channel is responsible for Cl- exit from the cell across the apical membrane.
此前的研究工作已经探究了气道上皮细胞跨上皮氯离子分泌的阴离子选择性及其被氯离子通道阻滞剂5-硝基-2-(3-苯丙基氨基)苯甲酸酯（NPPB）抑制的情况。在此，我们报告顶端膜和外向整流氯离子通道的阴离子选择性以及NPPB对氯离子通道的影响。在天然上皮细胞中用传统微电极测定的顶端膜的阴离子选择性顺序为：硫氰酸根离子＞碘离子＞溴离子＞硝酸根离子≈氯离子＞＞硫酸根离子≈葡萄糖酸根离子。这与氯离子和溴离子支持跨上皮分泌而碘离子不支持这一观察结果形成对比。因此，跨上皮转运的阴离子选择性是由基底外侧膜氯离子进入步骤决定的。在切除的膜片上研究的外向整流氯离子通道的阴离子选择性与顶端膜相同。我们还发现，NPPB能从膜片的内表面和外表面可逆地阻断外向整流氯离子通道。10微摩尔的NPPB能完全阻断该通道；较低浓度会导致通道处于开放状态的概率降低。NPPB还会使通道出现亚电导状态，而在没有NPPB的情况下很少观察到这种情况。这些数据进一步支持了外向整流氯离子通道负责氯离子从细胞穿过顶端膜排出这一结论。
