The production of phosphatidylinositol trisphosphate is stimulated by thrombin in human platelets

Untreated human platelets labeled to equilibrium with 32Pi contained undetectable levels of 3-phosphorylated phosphoinositides. Stimulation of platelets with thrombin for 5 min resulted in an enormous increase in the amount of phosphatidylinositol 3,4-bisphosphate (Nolan and Lapetina, J. Biol. Chem. 265, 2441–2445; 1990). We now report that the levels of phosphatidylinositol 3,4,5-trisphosphate are greatly elevated within 90 s of treatment of platelets with thrombin. Phosphatidylinositol 3,4,5-phosphate might have an important role in platelet aggregation.