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.
Mori
M
M
Department of Physiology, Kobe University, Japan.
Nishizaki
T
T
Kawahara
K
K
Okada
Y
Y
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002412:Cations / Q000378:metabolism*; D002460:Cell Line / Q000187:drug effects; D004533:Egtazic Acid / Q000494:pharmacology; D004848:Epithelium / Q000187:drug effects; D007668:Kidney / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D014981:Xenopus
D002412:Cations; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D002118:Calcium