Kitchens D L, Dawson K, Reuss L
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550.
Am J Physiol. 1990 May;258(5 Pt 1):G745-52. doi: 10.1152/ajpgi.1990.258.5.G745.
The effect of Zn2+ on Cl- transport across the apical membrane of Necturus gallbladder epithelium was studied with intracellular conventional and Cl(-)-selective microelectrodes and measurements of apparent base secretion. Most studies were done on tissues incubated in HEPES-buffered solutions; intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels were elevated by adding to the serosal bathing medium either theophylline or dibutyryl cAMP. Under these conditions, Zn2+ (added to mucosal solution) had no effect on membrane voltages, apparent cell membrane resistance ratio, or rapid depolarization induced by reducing mucosal solution [Cl-]. However, Zn2+ reduced the rate of cell membrane repolarization during exposure to the low-Cl- solution and decreased significantly the rate of fall of intracellular Cl- activity (alpha Cli) elicited by lowering mucosal solution [Cl-]. Both effects were time dependent, became significant after 10 min, and were slowly reversible. In tissues not stimulated by cAMP and incubated in a HCO3-CO2-buffered solution, Zn2+ also reduced the rate of fall of alpha Cli on lowering mucosal solution [Cl-]. Base secretion from cells to mucosal solution was assessed from changes in mucosal pH on stopping superfusion with a poorly buffered (1 mM HEPES) medium in the presence of 1 mM amiloride or a Na(+)-free medium, without cAMP stimulation. Exposure to Zn2+ reduced the alkalinization observed with both protocols. We conclude that Zn2+ has no effect on apical membrane Cl- conductance stimulated by cAMP and inhibits Cl(-)-HCO3- exchange. The slow onset and reversal of the effects suggests slow binding of Zn2+, a covalent modification of the exchanger, or an effect requiring Zn2+ transport to the cell interior.
采用细胞内传统微电极和氯离子选择性微电极，以及表观碱分泌测量方法，研究了锌离子（Zn2+）对美西螈胆囊上皮细胞顶端膜氯离子转运的影响。大多数实验是在含有羟乙基哌嗪乙磺酸（HEPES）缓冲液的溶液中孵育的组织上进行的；通过向浆膜浴液中添加茶碱或二丁酰环磷腺苷（cAMP）来提高细胞内3',5'-环磷酸腺苷（cAMP）水平。在这些条件下，添加到黏膜溶液中的Zn2+对膜电压、表观细胞膜电阻比或降低黏膜溶液中[Cl-]所诱导的快速去极化没有影响。然而，在暴露于低氯溶液期间，Zn2+降低了细胞膜复极化的速率，并显著降低了降低黏膜溶液中[Cl-]所引起的细胞内氯离子活性（αCli）下降速率。这两种效应都具有时间依赖性，在10分钟后变得显著，并且是缓慢可逆的。在未受cAMP刺激且在碳酸氢盐-二氧化碳缓冲溶液中孵育的组织中，Zn2+也降低了降低黏膜溶液中[Cl-]时αCli的下降速率。在存在1 mM氨氯吡脒的情况下，用缓冲性差的（1 mM HEPES）培养基停止灌流，或在无cAMP刺激的无钠培养基中，根据黏膜pH值的变化评估细胞向黏膜溶液的碱分泌。暴露于Zn2+会降低两种方案中观察到的碱化现象。我们得出结论，Zn2+对cAMP刺激的顶端膜氯离子电导没有影响，并抑制氯离子-碳酸氢根交换。这些效应的缓慢出现和逆转表明Zn2+的缓慢结合、交换体的共价修饰，或需要Zn2+转运到细胞内部的效应。
