Subcellular Regulation of Calcium Channel Currents in Renal Tubules.

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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.