FEEDBACK-REGULATION OF NA CHANNELS IN RAT CCT .1. EFFECTS OF INHIBITION OF NA PUMP
FEEDBACK-REGULATION OF NA CHANNELS IN RAT CCT .1. EFFECTS OF INHIBITION OF NA PUMP
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DOI：
10.1152/ajprenal.1993.264.3.f557
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发表时间：
1993-03-01
影响因子：
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通讯作者：
PALMER, LG
中科院分区：
文献类型：
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作者：
SILVER, RB;FRINDT, G;PALMER, LG
使用膜片钳技术研究了大鼠肾皮质集合管顶膜中的Na通道。在小管上的细胞贴附斑块中监测通道活动，这些小管被劈开以暴露管腔表面。在小管连续灌流过程中，在 37 摄氏度下测量通道数 (N)、开放概率 (P(o)) 和电流 (i)。添加哇巴因 (1 mM) 到上清液中以增加细胞 Na 浓度，导致开放通道平均数 (NP(o)) 在 2 分钟内减少至对照值的 20% 以下。去除哇巴因后 5 分钟内，这种效应不可逆转。此外，i 也平行减少。抑制机制似乎涉及细胞内 Ca (Ca(i)) 的增加。在与电测量相同的条件下，使用裂管主细胞中 Ca 指示剂 fura-2 的荧光测量 Ca(i)。添加哇巴因后约 3 分钟，Ca(i) 从基础水平 (153 +/- 36 nM) 增加至峰值水平 (588 +/- 53 nM)。当使用不含 Ca 的超融合液时，哇巴因不会增加 Ca(i) 或减少 NP(o)，尽管 i 的减少与在含 Ca 溶液中观察到的类似。在 0.1 mM 细胞外 Ca 存在下，Ca 离子载体离子霉素 (5 muM) 引起了类似的 Ca(i) 增加。该操作还导致 NP(o) 减少，这与哇巴因存在下观察到的情况类似。哇巴因对细胞 pH 值没有明显影响。我们的结论是，在哇巴因敏感的钠泵抑制钠从细胞中排出的过程中，由于钠/钙交换驱动力的变化，Ca(i) 升高。 Ca(i) 的增加可能通过间接机制抑制顶端 Na 通道。在这些情况下，其他因素（例如膜去极化）也可能导致 Na 通道抑制。
Na channels in the apical membrane of the rat renal cortical collecting tubule were studied using the patch-clamp technique. Channel activity was monitored in cell-attached patches on tubules that were split open to expose the luminal surface. Channel number (N), open probability (P(o)), and currents (i) were measured at 37-degrees-C during continuous superfusion of the tubule. Addition of ouabain (1 mM) to the superfusate to increase cell Na resulted in a decrease in the mean number of open channels (NP(o)) to less than 20% of control values within 2 min. This effect was not reversible within 5 min after removal of ouabain. There was, in addition, a parallel decrease in i. The mechanism of inhibition appeared to involve increased intracellular Ca (Ca(i)). Ca(i) was measured using the fluorescence of the Ca indicator fura-2 in principal cells of split tubules under conditions identical to those used for electrical measurements. Ca(i) increased from a basal level (153 +/- 36 nM) to a peak level (588 +/- 53 nM) approximately 3 min after the addition of ouabain. When a Ca-free superfusate was used, ouabain did not increase Ca(i) or decrease NP(o), although the decrease in i was similar to that observed in Ca-containing solutions. Similar increases in Ca(i) were elicited by the Ca ionophore ionomycin (5 muM) in the presence of 0.1 mM extracellular Ca. This maneuver also resulted in a decrease in NP(o) which was similar to that observed in the presence of ouabain. Ouabain had no observable effect on cell pH. We conclude that, during inhibition of Na exit from the cell by the ouabain-sensitive Na pump, Ca(i) rises as a result of changes in the driving forces for Na/Ca exchange. The increase in Ca(i) inhibits the apical Na channels, probably by an indirect mechanism. Other factors, such as membrane depolarization, may also contribute to Na channel inhibition under these circumstances.