Functionally diverse purinergic P2Y-receptors mediate prostanoid synthesis in cultured rat astrocytes: the role of ATP-induced phosphatidyl-inositol breakdown.

Abstract

Cultured rat astrocytes possess purinergic P2Y-receptors. Stimulation of these receptors with ATP (10(-3) M) results in increased phosphatidylinositol biphosphate (PIP2)-breakdown and prostanoid formation. We have investigated the relevance of the PIP2-pathway in prostanoid synthesis. The intracellular Ca(2+)-mobilizing agent thapsigargin (TG) (10(-6) M) and the diacylglycerol (DAG)-mimetic tetradecaoylphorbol acetate (TPA) (10(-8)-10(-6) M) both stimulate prostaglandin D2 production. ATP-induced prostanoid formation can be mimicked by combined addition of TG and TPA, suggesting the importance of the second messengers IP3 and DAG, generated during P2Y-receptor mediated PIP2-breakdown. Inhibition of ATP-induced PIP2-hydrolysis by TPA (IC50 about 5 x 10(-8) M) or by 10(-4) M neomycine, however, does not affect astroglial prostanoid synthesis, showing that P2Y-receptor mediated prostanoid formation may occur also in the absence of PIP2-hydrolysis. These findings suggest that additional postreceptor mechanisms exist in the signal transduction chain of ATP-induced astroglial prostanoid synthesis. A possible involvement of phospholipase A2 and/or of Ca(2+)-channels, directly coupled to P2Y-receptors is proposed.