Protease-activated receptor-4 (PAR4) belongs to a four-member family of GPCRs that are activated by proteases (see Ossovskaya et al for review). These proteases cleave a specific extracellular amino-terminal domain of the receptor to reveal a tethered ligand, which in turn activates the receptor which couples via Gq to release intracellular calcium (Nystedt, S. et al., 1995). PAR4 is expressed in the vasculature, GI tract, leukocytes, lung, and heart. PAR4 is a relevant target for coronary thromboses, inflammatory bowel disease and cancer.