Receptor-regulated formation of GTP[gamma S] with subsequent persistent Gs-protein activation in membranes of human platelets.

Preincubation of human platelet membranes with the ATP analog ATP[gamma S] led to persistent adenylate cyclase activation. This stimulation was increased by copreincubation with PGE1 and obliterated by removing endogenous GDP by the NTP-regenerating system, creatine phosphate plus creatine kinase. PGE1 partially reversed the action of the regenerating system. Control formation of GTP[gamma S] from ATP[gamma S] and GDP in platelet membranes was apparently not stimulated by PGE1. In contrast, in the presence of creatine phosphate plus creatine kinase, which prevented formation of GTP[gamma S], PGE1 stimulated formation of this GTP analog, by partially reversing the action of the NTP-regenerating system. The data indicate that GTP[gamma S] can be formed by a membrane-associated nucleoside diphosphokinase from ATP[gamma S] and GDP, resulting in persistent Gs-protein activation, and that this process can be stimulated by an agonist-activated receptor.