Stimulation of high-affinity hormone-sensitive GTPase of human platelets by 1-O-alkyl-2-O-acetyl-sn-glyceryl-3-phosphocholine (platelet activating factor)

1-O-Alkyl-2-O-acetyl-sn-glyceryl-3-phosphocholine (platelet activating factor) inhibits human platelet adenylate cyclase via the GTP-dependent mechanism. Inhibition of adenylate cyclase correlates with the stimulation of high affinity hormone-sensitive GTPase. The half-maximal effects of PAF on both enzymes are observed at concentrations about 10(-8) M. Phentolamine, an alpha-adrenergic antagonist, does not abolish the PAF-induced inhibition of adenylate cyclase. The obtained data suggest that PAF receptors are coupled with the GTP-binding inhibitory protein.