P-2 PURINOCEPTOR-MEDIATED STIMULATION OF ADENYLYL-CYCLASE IN PC12 CELLS

PC12 pheochromocytoma cells have P-2 purinoceptors which are activated by ATP and coupled to Ca2+ influx and catecholamine release. Also PC1 2 cells have adenosine receptors coupled positively to adenylyl cyclas e, and cyclic AMP regulates cell functions such as catecholamine relea se. The effects of ATP and ATP analogs on cyclic AMP accumulation in P C12 cells were investigated in this study. ATP and adenosine 5'-O-(3-t hiotriphosphate) stimulated cyclic AMP accumulation at low concentrati ons up to 300 mu M but showed inhibitory effects above this concentrat ion. 2',3'-O-(4-Benzoyl)benzoyl ATP and 2-methylthio ATP showed simila r effects, although the responses were very limited. Addition of adeno sine 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 d eaminase or specific antagonists to A(1) and A(2) adenosine receptors. Neither ADP beta S nor beta,gamma-methylene ATP showed any effect on Ca2+ influx or noradrenaline release. Suramin, a P-2 receptors antagon ist, had no inhibitory effect against ATP analog-stimulated cyclic AMP accumulation, although reactive blue 2 inhibited the beta,gamma-methy lene ATP-stimulated reaction but not that up-regulated by ADP beta S. These findings suggest that the pharmacological characteristics of the se ATP receptors coupled to adenylyl cyclase are clearly different fro m those of ligand-gated ion channels defined by P-2X purinoceptors, wh ich have been cloned and shown to be coupled to Ca2+ influx and catech olamine release in PC12 cells. The existence of a new type of P-2 puri noceptor-mediating stimulation of adenylyl cyclase is proposed in PC12 cells.