K depletion enhances the extracellular Ca2+-induced inhibition of the apical K channels in the mTAL of rat kidney
K depletion enhances the extracellular Ca2+-induced inhibition of the apical K channels in the mTAL of rat kidney
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DOI：
10.1085/jgp.119.1.33
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发表时间：
2002-01-01
影响因子：
3.8
通讯作者：
Wang, WH
中科院分区：
文献类型：
--
作者：
Gu, RM;Wei, Y;Wang, WH
我们以前已经证明，升高细胞外钙离子抑制了粗大升肢顶端70-PS钾通道(TAL；Wang，W.H.，M.Lu和S.C.Hebert)。1996年。上午好。J.Physiol.270：C103-C111)。我们用膜片钳技术研究了细胞外钙离子浓度增加对不同钾饮食大鼠mTAL膜上70-pS钾通道的影响。低钾(KD)饲料大鼠mTAL前部细胞外钙离子浓度从10 mM增加到0.5、1和1.5 mM时，通道活性分别降低30%、65%和90%，而高K(HK)饲料大鼠mTAL细胞外钙离子浓度从1.5 mM增加到2.5、3.5和5.5 mM时，通道活性分别降低29、55和90%。细胞色素P450单加氧酶的抑制可完全消除细胞外钙离子对不同钾饮食大鼠mTAL通道活性的影响。相反，阻断环氧合酶并不能显著改变70-pS钾通道对细胞外钙离子的反应。此外，加入一氧化氮(NO)供体硝普钠不仅可增加通道活性，还可钝化细胞外钙离子对70-pS钾通道的抑制作用，并降低20-羟基二十碳四烯酸(20-HETE)浓度。而L-NAME对一氧化氮合酶的抑制作用则增强了细胞外钙离子对通道活动的抑制作用，并增加了高钾饮食大鼠脑内20-HETE的浓度。Western印迹进一步表明，肾髓质中诱导型一氧化氮合酶(INOS)的表达明显高于KD饮食的大鼠。加入S-亚硝基-N-乙酰青霉胺可阻断花生四烯酸对MTAL通道活动的抑制作用，但不阻断20-HETE的抑制作用。我们的结论是，低钾摄入量增加了70-pS钾通道对细胞外钙离子的敏感性，在钾缺乏时，细胞外钙离子对通道活性的抑制作用与一氧化氮合酶活性的降低有关。
We have shown previously that raising extracellular Ca2+ inhibited the apical 70-pS K channel in the thick ascending limb (TAL; Wang, W.H., M. Lu, and S.C. Hebert. 1996. Am. J. Physiol. 270:C103-C111). We now used the patch-clamp technique to study the effect of increasing the extracellular Ca2+ on the 70-pS K channel in the mTAL from rats on a different K diet. Increasing the extracellular Ca2+ from, 10 muM to 0.5, 1, and to 1.5 mM in the mTAL front rats on a K-deficient (KD) diet inhibited the channel activity by 30, 65, and 90%, respectively, In contrast, raising the extracellular Ca2+ to 1.5 mM had no significant effect on channel activity in the mTAL from animals on a high K (HK) diet and further increasing the extracellular Ca2+ to 2.5, 3.5, and 5.5 mM decreased the channel activity by 29, 55, and 90%, respectively. Inhibition of the cytochrome P450 monooxygenase completely abolished the effect of the extracellular Ca2+ on channel activity in the mTAL from rats on a, different K diet. In contrast, blocking cyclooxygenase did not significantly alter the responsiveness of the 70-pS K channel to the extracellular Ca2+. Moreover, addition of sodium nitropruside, a nitric oxide (NO) donor, not only increased the channel activity, but also blunted the inhibitor, effect of the extracellular Ca2+ on the 70-pS K channel and decreased 20-hydroxyeicosatetraenoic acid (20-HETE) concentration in the mTAL front rats on a KD diet. In contrast, inhibiting NOS with L-NAME enhanced the inhibitory effect of the extracellular Ca2+ on the channel activity and increased 20-HETE concentration in the mTAL front rats on a high K diet. Western blot has further shown that the expression of inducible NO synthase (iNOS) is significantly higher in the renal medulla from rats on an HK diet than that on a KD diet. Also, addition of S-nitroso-N-acetylpenicillamine abolished the inhibitory effect of arachidonic acid on channel activity in the MTAL, whereas it did not block the inhibitory effect of 20-HETE. We conclude that a low dietary K intake increases the sensitivity of the 70-pS K channel to the extracellular Ca2+ and that a decrease in NOS activity is involved in enhancing the inhibitory effect of the extracellular Ca2+ on channel activity, in the mTAL during K depletion.