ATP-activated cation conductance in a Xenopus renal epithelial cell line.

1. Using a whole-cell voltage-clamp technique and fura-2 fluorescence measurements, the actions of extracellular adenosine 5'-triphosphate (ATP) in single cells of an epithelial cell line (A6), were investigated. 2. ATP (0.1-1000 microM) induced currents in cells held under voltage clamp. The sequence of purinergic agonist potency in activating the currents (2-methylthio ATP > adenosine 5'-diphosphate (ADP) > ATP > alpha, beta-methylene ATP) was consistent with that of P2y receptors. 3. Reversal potentials (Erev) of the currents under various ionic conditions suggest that potassium channels and non-selective cation channels were responsible for the ATP-activated conductance, which was permeable to calcium. 4. ATP activated the currents in a calcium-free extracellular solution. In the presence of extracellular calcium, the currents were completely inhibited with 10 mM EGTA in the pipette. 5. ATP (10 microM) increased the intracellular calcium concentration ([Ca2+]i) whether cells were bathed in a solution containing calcium or not. 6. These results indicate that ATP evoked a calcium-dependent cation conductance, permeable to calcium, through P2y receptors by releasing calcium from intracellular stores in A6 cells.