Proteinase-activated receptor 4 (PAR(4)): action of PAR(4)-activating peptides in vascular and gastric tissue and lack of cross-reactivity with PAR(1) and PAR(2)

We studied the actions of the human and murine proteinase-activated recepto r 4 PAR(4) derived receptor-activating peptides (APs), GYPGQV-NH2, (GQV-NH2 ,) and GYPGKF-NH2 (GKF-NH2,), (i) to activate-desensitize either PARI or PA R(2) in cultured cell systems (calcium signalling in PAR,/PAR(2),-bearing h uman HEK cells and in rat KNRK cells expressing either rat or human PAR) an d (ii) to affect contractility in rat aorta (RA) and rat gastric longitudin al muscle (LM) preparations in vitro. We found that neither PAR, nor PAR, w as affected by concentrations of the PAR(4)-APs (800 mu M) that caused both an endothelium-dependent nitric oxide mediated relaxation of preconstricte d RA tissue and a contractile response in the LM preparation. The potencies (EC50 values 300 to 400 mu M) of GQV-NH2, and GKF-NH2 for causing a relaxa nt effect were identical and comparable with the potency of GQV-NH2 for cau sing a contractile effect in the LM. However, the potencies of thk PAR(4)-A Ps in the RA and LM preparations were 20- to 150-fold lower than the potenc y of the receptor-selective PAR(1)-AP, TFLLR-NH2. We conclude that the PAR( 4)-APs do not activate either PAR(1) or PAR(2) and we suggest that along wi th PAR(1) and PAR(2) PAR(4) may also be present in rat vascular and gastric smooth muscle.