Purinergic control of apical plasma membrane PI(4,5)P2 levels sets ENaC activity in principal cells
Purinergic control of apical plasma membrane PI(4,5)P2 levels sets ENaC activity in principal cells
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DOI：
10.1152/ajprenal.00403.2007
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发表时间：
2008-01-01
影响因子：
4.2
通讯作者：
Stockand, James D.
中科院分区：
文献类型：
--
作者：
Pochynyuk, Oleh;Bugaj, Vladislav;Stockand, James D.
上皮钠通道（ENaC）的活性限制了远端肾元的Na+重吸收。磷酸肌醇，如磷脂酰肌醇4,5-二磷酸[PI(4,5)P-2]调节该通道的活性。嘌呤能受体的激活触发多种事件，包括PKC和PLC的激活，后者消耗质膜PI(4,5)P-2。在这里，我们研究了嘌呤能受体通过PLC和PI(4,5)P-2对肾主细胞ENaC的调节。嘌呤能信号迅速降低ENaC打开概率和根尖膜PI(4,5)P-2水平，且时间过程相似。此外，用苏拉明抑制嘌呤能信号传导可以挽救ENaC活性。PLC抑制剂U73122，而不是U73343，它的非活性类似物，再现苏拉明的作用。相比之下，调节PKC信号传导不能影响ENaC的嘌呤能调节。出乎意料的是，在静息细胞中抑制嘌呤能受体或PLC均可显著提高ENaC活性，高于基础水平，表明这些极化的肾上皮细胞中嘌呤能信号的强性激活。ENaC活性增加与根尖膜PI(4,5)P-2水平升高有关。在嘌呤能信号被抑制的情况下，随后用ATP处理未能降低ENaC活性和根尖膜PI(4,5)P-2水平。停留时间分析表明，PI(4,5)P-2的耗尽迫使ENaC走向封闭状态。相比之下，增加高于基础值的PI(4,5)P-2水平将通道锁定在由短暂关闭中断的开放状态。因此，我们的研究结果表明，嘌呤能控制的顶膜PI(4,5)P-2水平是肾上皮细胞ENaC活性的主要调节因子。
Activity of the epithelial sodium channel (ENaC) is limiting for Na+ reabsorption at the distal nephron. Phosphoinositides, such as phosphatidylinositol 4,5-biphosphate [PI(4,5)P-2] modulate the activity of this channel. Activation of purinergic receptors triggers multiple events, including activation of PKC and PLC, with the latter depleting plasma membrane PI(4,5)P-2. Here, we investigate regulation of ENaC in renal principal cells by purinergic receptors via PLC and PI(4,5)P-2. Purinergic signaling rapidly decreases ENaC open probability and apical membrane PI(4,5)P-2 levels with similar time courses. Moreover, inhibiting purinergic signaling with suramin rescues ENaC activity. The PLC inhibitor U73122, but not U73343, its inactive analog, recapitulates the action of suramin. In contrast, modulating PKC signaling failed to affect purinergic regulation of ENaC. Unexpectedly, inhibiting either purinergic receptors or PLC in resting cells dramatically increased ENaC activity above basal levels, indicating tonic activation of purinergic signaling in these polarized renal epithelial cells. Increased ENaC activity was associated with elevation of apical membrane PI(4,5)P-2 levels. Subsequent treatment with ATP in the presence of inhibited purinergic signaling failed to decrease ENaC activity and apical membrane PI(4,5)P-2 levels. Dwell-time analysis reveals that depletion of PI(4,5)P-2 forces ENaC toward a closed state. In contrast, increasing PI(4,5)P-2 levels above basal values locks the channel in an open state interrupted by brief closings. Thus our results suggest that purinergic control of apical membrane PI(4,5)P-2 levels is a major regulator of ENaC activity in renal epithelial cells.