THE THROMBIN RECEPTOR IN HUMAN PLATELETS IS COUPLED TO A GTP-BINDING PROTEIN OF THE G-ALPHA(Q) FAMILY

The thrombin receptor is a G protein-coupled receptor, but the G prote ins functionally coupled to this receptor in human platelets are not y et definitively identified. Thrombin stimulation of platelets leads to phospholipase C-mediated increases in intracellular calcium, and prev ious studies have suggested that the thrombin receptor is coupled to m embers of the G(q) family. We now demonstrate direct GTPase activation by thrombin receptor activation peptide (TRAP) in human platelet memb ranes, and specific inhibition of TRAP-activated GTPase by antibodies to G(q). These data demonstrate functional coupling of the thrombin re ceptor to a member of the G(q) family.