Subcellular Regulation of Calcium Channel Currents in Renal Tubules.

本研究应用膜片钳技术对体外培养的肾小管上皮细胞（A6细胞）的钙通道进行了研究。移液管溶液含有（以mM计）Nagluconate 100、NaCl 20、MgCl_2 1、NaHEPES（pH 7.4）10、EGTA 0.1-5。浴含有正常的两栖动物溶液或无钙溶液。在全细胞钳记录中，在Cl平衡电位（E_2 =-47mV）下，ATP（0.2-20 μ M）作用于细胞可诱发内向阳离子电流<cl>。当移液管含有5 mM EGTA并且将细胞置于无Ca溶液中时，电流几乎完全消除。用百日咳毒素（1 μ g/ml）预处理细胞，在细胞外Ca不存在的情况下减慢内向电流的激活，但在细胞外Ca存在的情况下不减慢。当用CaCl_2（45）或CaCl_2（22.5）+ MnCl_2（22.5）（单位：mM）完全替代NaCl时，ATP在E_（-37 mV）诱发Ca和/或Mn电流<cl>。结论：外源性ATP开放了对细胞内Ca ~（2+）活性敏感的Ca ~（2+）、Mn ~（2+）离子通道。

I have used the patch-clamp technique to identify and study Ca permeable channels in cultured renal distal tubule cells (A6 cells). The pipette solutions contained (in mM) Nagluconate 100, NaCl 20, MgCl_2 1, NaHEPES (pH 7.4) 10, EGTA 0.1-5. The bath either contained a normal amphibian solution or a Ca free solution. In the whole-cell clamp recording, the inward cation currents were induced by application of ATP (0.2-20 uM) to the cell at the equilibrium potential of Cl (E_<cl>=-47 mV). The currents were almost completely abolished when the pipette contained 5 mM EGTA and the cells were placed in a Ca free solution. Pretreatment of the cells with pertussis toxin (1 ug/ml)slowed the activation of the inward currents in the absence but not in the presence of extracellular Ca. When NaCl was totally replaced by CaCl_2 (45) or CaCl_2 (22.5) + MnCl_2 (22.5)(in mM), the Ca and/or Mn currents were evoked by ATP at E_<cl> (-37 mV). Conclusion: The external ATP opens the Ca and Mn permeable cation channel which is sensitive to the intracellular Ca activity.