Platelet-activating factor (PAF) stimulates phosphatidylinositol hydrolysis in human peripheral blood mononuclear...

Human peripheral blood mononuclear leukocytes were labeled with myo-[3H]inositol and stimulated by platelet-activating factor (PAF). PAF-induced phosphatidylinositol hydrolysis and inositol-1,4,5-trisphosphate (IP3) formation in a dose-dependent manner. The response was very rapid and transient and parallels the time course of PAF-induced calcium mobilization in the same cells. However, the doses of PAF for inducing IP3 formation were much higher than those for calcium mobilization. PAF-induced IP3 formation was inhibited by PAF receptor antagonist, L-659, 989, but was not altered by either pertussis toxin or cholera toxin. These data suggest that PAF receptor in human peripheral blood mononuclear leukocytes may be coupled through a pertussis toxin-insensitive guanine nucleotide binding protein to a phosphoinositide-specific phospholipase C.