P2 PURINOCEPTOR LOCALIZATION ALONG RAT NEPHRON AND EVIDENCE SUGGESTING EXISTENCE OF SUBTYPES P2Y(1) AND P2Y(2)

Effects of extracellular ATP on intracellular free calcium concentrati on ([Ca2+](i)) were examined in rat single nephron segments using the fura 2-AM. ATP (10 mu M) induced a significant transient increase in [ Ca2+](i) in the glomerulus, the early proximal convoluted tubule (S1), the cortical collecting tubule (CCT), and the outer medullary collect ing tubule (OMCT). The magnitude of the response was the greatest in t he OMCT among four segments. ATP induced an increase in the [Ca2+](i) in a dose-dependent manner in S1 and OMCT. In the OMCT, ATP caused a b iphasic increase in [Ca2+](i) consisting of an initial rapid rise and a sustained phase. Removal of calcium from the medium resulted in an a ttenuation of the sustained phase of [Ca2+](i) and an similar to 30% r eduction in the height of the initial [Ca2+](i) peak in response to 10 mu M ATP. Effects of ATP, its analogs, and its metabolites were teste d in the S1 and OMCT. ATP, 2-methylthio-ATP (2-MeS-ATP), ADP, and UTP increased [Ca2+](i) dose dependently. AMP and adenosine did not affect [Ca2+](i) in the S1 and OMCT. The ATP- or 2-MeS-ATP-induced [Ca2+](i) increase was inhibited by the pretreatment of the S1 and OMCT with su ramin or reactive blue 2. Neomycin, a phospholipase C inhibitor, atten uated the ATP-induced [Ca2+](i) increase. To investigate the hormoneli ke action of ATP in OMCT, a heterologous cross desensitization was per formed. The pretreatment of OMCT with ATP inhibited increases in vasop ressin-, ANG II-, endothelin-1-, or bradykinin-induced [Ca2+](i) incre ase. These findings suggest that ATP might affect the above peptidyl a gonist-activated calcium mobilizations.