Role of PAR-1 in thrombin-induced platelet procoagulant activity.

Inhibition of thrombin-induced procoagulant activity by the partial PAR-1 agonist YFFLRNP, by the peptide bradykinin, and by MoAb IIaR-A against the PAR-1 receptor; gel-filtered platelets were incubated with YFLLRNP (100 μmol/L) or with bradykinin (1 μmol/L) or with MoAb IIaR-A (20 μg/mL) and activated with thrombin (0.05-2 U/mL); ● indicates 25 000 platelets/μL; ○, 25 000 platelets/μL in presence of YFLLRNP; ■, 25 000 platelets/μL in the presence of bradykinin; ▵, 25 000 platelets/μL in the presence of MoAb IIaR-A. The fluorescence of 5000 platelets per measuring point was determined by flow cytometry. Data are the mean of 3 experiments using platelets from different donors.