[Mechanism of action of protease-activated receptors 1 and 4 in platelet activation].

This study was designed to compare the effects of protease-activated receptor 1 (PAR-1) and protease-activated receptor 4 (PAR-4) to the expression of platelet surface GPIbalpha and cytoskeleton reorganization, then to investigate the role of PARs in platelet signal transmission. PAR1 (25 micromol/L) and PAR4 (250 micromol/L) were used to stimulate platelet at different time points (0 - 60 minutes), and the platelet surface GPIbalpha, actin and myosin and P-selectin were detected with flow cytometry, the alteration of GPIbalpha, actin and myosin in cytoskeleton was compared by Western blot, the membrane cytoskeleton followed GPIbalpha immunoprecipitation was analyzed. The results showed that an increase of P-selectin and reversible decrease of GPIbalpha expression were obtained after platelet activation by PAR1 o r PAR4, and a different kinetics of redistribution of GPIbalpha was found for the two peptides all over the time course (P < 0.05). PAR1 acted more potently and rapidly than PAR4, but the effect of PAR4 persisted longer in the course of platelet activation. Meanwhile, there was a transient change of actin, myosin and GPIbalpha in cytoskeleton proteins. Similar redistribution was also found in GPIbalpha/myosin and GPIbalpha/actin association. It is concluded that PAR1 and PAR4 possess an important role in platelet signal transmission. Either of the receptors can mediate platelet activation and GPIbalpha redistribution, which is correlated with cytoskeleton reorganization. PAR1 acts more rapidly, and effect of PAR4 persists longer.