Amiloride-sensitive trypsinization of apical sodium channels. Analysis of hormonal regulation of sodium transport in toad bladder.
Amiloride-sensitive trypsinization of apical sodium channels. Analysis of hormonal regulation of sodium transport in toad bladder.
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DOI：
10.1085/jgp.81.6.785
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发表时间：
1983-06
期刊：
影响因子：
--
通讯作者：
Edelman IS
中科院分区：
文献类型：
--
作者：
Garty H;Edelman IS
孵育的蟾蜍膀胱粘膜表面与胰蛋白酶（1毫克/毫升）不可逆地减少短路电流的50%的初始值。这种减少是伴随着顶端Na渗透性成比例减少，估计从去极化制剂中阿米洛利敏感性电阻的变化。相反，细胞旁阻力不受胰蛋白酶消化。阿米洛利，一个特定的顶端钠通道阻滞剂，防止胰蛋白酶失活。然而，抑制钠转运粘膜钠的替代，胰蛋白酶的反应没有影响。胰蛋白酶消化的顶膜也被用来研究钠转运的抗利尿激素（ADH）和醛固酮的调节。先前暴露于胰蛋白酶的顶端表面没有减少对ADH的反应，这表明ADH诱导的Na通道在添加激素之前无法接近胰蛋白酶。另一方面，刺激的短路电流的醛固酮或丙酮酸（添加到基板耗尽，醛固酮充满膀胱）大大减少了前胰蛋白酶消化的顶端表面。因此，顶端Na渗透性的增加引起的醛固酮或底物涉及激活Na通道，连续存在于顶端膜中的非导电，但胰蛋白酶敏感的形式。
Incubation of the mucosal surface of the toad urinary bladder with trypsin (1 mg/ml) irreversibly decreased the short-circuit current to 50% of the initial value. This decrease was accompanied by a proportionate decrease in apical Na permeability, estimated from the change in amiloride-sensitive resistance in depolarized preparations. In contrast, the paracellular resistance was unaffected by trypsinization. Amiloride, a specific blocker of the apical Na channels, prevented inactivation by trypsin. Inhibition of Na transport by substitution of mucosal Na, however, had no effect on the response to trypsin. Trypsinization of the apical membrane was also used to study regulation of Na transport by anti-diuretic hormone (ADH) and aldosterone. Prior exposure of the apical surface to trypsin did not reduce the response to ADH, which indicates that the ADH-induced Na channels were inaccessible to trypsin before addition of the hormone. On the other hand, stimulation of short-circuit current by aldosterone or pyruvate (added to substrate-depleted, aldosterone-repleted bladders) was substantially reduced by prior trypsinization of the apical surface. Thus, the increase in apical Na permeability elicited by aldosterone or substrate involves activation of Na channels that are continuously present in the apical membrane in nonconductive but trypsin-sensitive forms.