IDENTIFICATION OF A P2Y-PURINERGIC RECEPTOR THAT INHIBITS ADENYLYL-CYCLASE

Adenine nucleotides inhibited isoproterenol- and forskolin-stimulated cyclic AMP accumulation in C6-2B rat glioma cells. Inhibition occurred in the presence of a phosphodiesterase inhibitor, and no effect of ad enine nucleotides was observed in direct measurements of phosphodieste rase activity in intact cells. Pretreatment of C6-2B glioma cells with pertussis toxin blocked the inhibitory effects of P2Y-purinergic rece ptor agonists. The pharmacological specificity for a series of ATP and ADP analogs (2-methylthioadenosine 5'-triphosphate greater-than-or-eq ual-to 2-methylthioadenosine 5'-diphosphate > adenosine 5'-O-(2-thiodi phosphate) > 2-chloro-adenosine 5'-triphosphate = ADP = adenosine 5'-O -(3-thiotriphosphate) > ATP > UTP) was similar to that expected of a P 2Y-purinergic receptor; the P2X-purinergic receptor agonists, alpha,be ta-methyleneadenosine 5'-triphosphate and beta,gamma-methylene-adenosi ne 5'-triphosphate, had no effect. Because activation of phospholipase C occurs in response to P2-purinergic receptor activation in many tar get tissues, the effects of P2Y-receptor agonists on inositol phosphat e accumulation were measured in C6-2B cells. No evidence for P2Y-purin ergic receptor-mediated regulation of inositol lipid metabolism was ob served under conditions where muscarinic cholinergic receptor activati on or AlF4-markedly increased inositol phosphate accumulation. These r esults suggest that a P2-purinergic receptor subtype with distinct sig naling properties exists on C6-2B rat glioma cells. Although this rece ptor expresses the general pharmacological specificity of a phospholip ase C-coupled P2Y-purinergic receptor, it may represent a unique recep tor subtype since it inhibits adenylyl cyclase.