Extracellular ATP increases [CA(2+)](i) in distal tubule cells. I. Evidence for a P2Y2 purinoceptor

Experiments were performed to characterize the P2 purinoceptor subtype resp onsible for cytoplasmic calcium mobilization in cells from the initial part of rabbit distal convoluted tubule (DCT). Free calcium concentration was m easured in a DCT cell line (DC1) with the probe fura 2. Both ATP and UTP in creased cytosolic Ca2+ concentration ([Ca2+](i); EC50 3 and 6 mu M, respect ively). The order of potency for nucleotide analogs was ATP = UTP > adenosi ne 5'-O-[thiotriphosphate] >> ADP > UDP, which is consistent with the pharm acology of the P2Y2 receptor subtype. The increased [Ca2+](i) responses to ATP and UTP were strongly inhibited by suramin. Pretreatment of cells with pertussis toxin (PTX) attenuated the action of both nucleotides. Inhibition of phospholipase C with U-73122 totally blocked the [Ca2+](i) response to ATP. Thus ATP- and UTP-stimulated [Ca2+](i) mobilization in DC1 cells appea rs to be mediated via the activation of P2Y2 purinoceptors coupled to a G p rotein mechanism that is partially sensitive to PTX. Calcium flux measureme nts showed that lanthanum- and nifedipine-sensitive calcium channels are in volved in the [Ca2+](i) response to ATP.