Kong Shumin, Zhang Chengbiao, Li Wennan, Wang Lijun, Luan Haiyan, Wang Wen-Hui, Gu Ruimin
Department of Pharmacology, Harbin Medical University, Harbin 150086, China.
Biochim Biophys Acta. 2012 Feb;1823(2):273-81. doi: 10.1016/j.bbamcr.2011.10.007. Epub 2011 Oct 25.
We used the patch-clamp technique to study the effect of changing the external Ca2+ on the basolateral 50-pS K channel in the thick ascending limb (TAL) of rat kidney. Increasing the external Ca2+ concentration from 1 mM to 2 or 3 mM inhibited the basolateral 50-pS K channels while decreasing external Ca2+ to 10 μM increased the 50-pS K channel activity. The effect of the external Ca2+ on the 50-pS K channels was observed only in cell-attached patches but not in excised patches. Moreover, the inhibitory effect of increasing external Ca2+ on the 50-pS K channels was absent in the presence of NPS2390, an antagonist of Ca2+-sensing receptor (CaSR), suggesting that the inhibitory effect of the external Ca2+ was the result of stimulation of the CaSR. Application of the membrane-permeable cAMP analog increased the 50-pS K channel activity but did not block the effect of raising the external Ca2+ on the K channels. Neither inhibition of phospholipase A2 (PLA2) nor suppression of cytochrome P450-ω-hydroxylation-dependent metabolism of arachidonic acid was able to abolish the effect of raising the external Ca2+ on the 50-pS K channels. In contrast, inhibition of phospholipase C (PLC) or blocking protein kinase C (PKC) completely abolished the inhibition of the basolateral 50-pS K channels induced by raising the external Ca2+. We conclude that the external Ca2+ concentration plays an important role in the regulation of the basolateral K channel activity in the TAL and that the effect of the external Ca2+ is mediated by the CaSR which stimulates PLC-PKC pathways. The regulation of the basolateral K channels by the CaSR may be the mechanism by which extracellular Ca2+ level modulates the reabsorption of divalent cations.
我们运用膜片钳技术研究了改变细胞外钙离子（Ca2+）浓度对大鼠肾髓袢升支粗段（TAL）基底外侧50-pS钾通道的影响。将细胞外Ca2+浓度从1 mM提高到2 mM或3 mM会抑制基底外侧50-pS钾通道，而将细胞外Ca2+浓度降低至10 μM则会增加50-pS钾通道的活性。细胞外Ca2+对50-pS钾通道的影响仅在细胞贴附式膜片中观察到，而在切除式膜片中未观察到。此外，在存在Ca2+ 感受受体（CaSR）拮抗剂NPS2390的情况下，提高细胞外Ca2+ 对50-pS钾通道的抑制作用消失，这表明细胞外Ca2+ 的抑制作用是刺激CaSR的结果。应用可透过细胞膜的环磷酸腺苷（cAMP）类似物可增加50-pS钾通道的活性，但不会阻断提高细胞外Ca2+ 对钾通道的影响。抑制磷脂酶A2（PLA2）或抑制细胞色素P450-ω-羟基化依赖性花生四烯酸代谢均无法消除提高细胞外Ca2+ 对50-pS钾通道的影响。相反，抑制磷脂酶C（PLC）或阻断蛋白激酶C（PKC）可完全消除提高细胞外Ca2+ 诱导的基底外侧50-pS钾通道的抑制作用。我们得出结论，细胞外Ca2+ 浓度在调节TAL基底外侧钾通道活性中起重要作用，且细胞外Ca2+ 的作用是由刺激PLC-PKC途径的CaSR介导的。CaSR对基底外侧钾通道的调节可能是细胞外Ca2+ 水平调节二价阳离子重吸收的机制。
