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 proteins functionally coupled to this receptor in human platelets are not yet definitively identified. Thrombin stimulation of platelets leads to phospholipase C-mediated increases in intracellular calcium, and previous studies have suggested that the thrombin receptor is coupled to members of the Gq family. We now demonstrate direct GTPase activation by thrombin receptor activation peptide (TRAP) in human platelet membranes, and specific inhibition of TRAP-activated GTPase by antibodies to Gq. These data demonstrate functional coupling of the thrombin receptor to a member of the Gq family.