P2 purinoceptor-mediated stimulation of adenylyl cyclase in PC12 cells

PC12 pheochromocytoma cells have P2 purinoceptors which are activated by ATP and coupled to Ca2+ influx and catecholamine release. Also PC12 cells have adenosine receptors coupled positively to adenylyl cyclase, and cyclic AMP regulates cell functions such as catecholamine release. The effects of ATP and ATP analogs on cyclic AMP accumulation in PC12 cells were investigated in this study. ATP and adenosine 5'-0-(3-thiotriphosphate) stimulated cyclic AMP accumulation at low concentrations up to 300 microM but showed inhibitory effects above this concentration. 2',3'-O-(4-Benzoyl)benzoyl ATP and 2-methylthio ATP showed similar effects, although the responses were very limited. Addition of adenosine 5'-O-(2-thiodiphosphate) (ADP beta S) or beta, gamma-methylene ATP, but not alpha, beta-methylene ATP, stimulated cyclic AMP accumulation markedly without causing an inhibitory phase. The effects of ATP, ADP beta S and beta, gamma-methylene ATP were not inhibited by adenosine deaminase or specific antagonists to A1 and A2 adenosine receptors. Neither ADp beta S nor beta, gamma-methylene ATP showed any effect on Ca2+ influx or noradrenaline release. Suramin, a P2 receptors antagonists, had no inhibitory effect against ATP analog-stimulated cyclic AMP accumulation, although reactive blue 2 inhibited the beta, gamma-methylene ATP-stimulated reaction but not that up-regulated by ADP beta S. These findings suggest that the pharmacological characteristics of these ATP receptors coupled to adenylyl cyclase are clearly different from those of ligand-gated ion channels defined by P2X purinoceptors, which have been cloned and shown to be coupled to Ca2+ influx and catecholamine release in PC12 cells. The existence of a new type of P2 purinoceptor-mediating stimulation of adenylyl cyclase is proposed in PC12 cells.