Effects of ATP on Phosphoinositide Hydrolysis and Prostaglandin E2 Generation in Rabbit Astrocytes

Extracellular ATP secreted from stimulated nerves plays a role in neurotransmission. This study examined the effects of extracellular ATP on phospholipase A2 and C signalling pathways in rabbit astrocytes. ATP caused prostaglandin E2 (PGE2) generation and phosphoinositide hydrolysis in a time- and concentration-dependent manner. A P2y purinoceptor-selective agonist, 2-methylthio-ATP also caused phosphoinositide hydrolysis, but not PGE2 generation. A P2x purinoceptor-selective agonist, alpha, beta-methylene-ATP did not cause either phosphoinositide hydrolysis or PGE2 generation. Although pertussis toxin had no effect on 2-methylthio-ATP-induced phosphoinositide hydrolysis, it markedly decreased ATP-induced PGE2 generation, with significant inhibition of phosphoinositide hydrolysis. Dexamethasone and indomethacin which potently inhibited ATP-induced PGE2 generation, caused partial inhibition of phosphoinositide hydrolysis, suggesting that pertussis toxin-sensitive component of ATP-induced phospholipase C activation is mediated by cyclo-oxygenase metabolites of arachidonic acid. These results suggest that a stimulation of P2y receptor results in phospholipase C activation in a pertussis toxin-insensitive manner, and that a P2 receptor other than the P2y or P2x subtypes is involved in ATP-induced phospholipase A2 activation via a pertussis toxin-sensitive G protein.