alpha(IIb)beta(3)-integrin mediated adhesion of human platelets to a fibrinogen matrix triggers phospholipase C activation and phosphatidylinositol 3',4'-bisphosphate accumulation

This study focused on the variations in phosphoinositide metabolism depending upon alpha(IIb)beta(3)-integrin/fibrinogen interaction without previous activation of platelet agonist receptors. We found that adhesion of resting human platelets to immobilized fibrinogen stimulates phosphatidic acid production and a concomitant decrease in phosphatidylinositol 4',5'-bisphosphate. These results, and the absence of a transphosphatidylation reaction, argue in favor of the activation of a phospholipase C. Moreover, we observed the accumulation of phosphatidylinositol 3',4'-bisphosphate in adherent platelets as a consequence of the activation of a phosphatidylinositol 3-kinase. This effect was inhibited by ADP scavengers, Our results demonstrate that in adherent platelets, whereas phosphatidylinositol 3-kinase activation is controlled by both alpha(IIb)beta-integrin engagement and released ADP, phospholipase C stimulation is triggered only by alpha(IIb)beta-integrin/fibrinogen interaction.