(A) Despite calcium mobilization through PAR-1 and PAR-4, platelet activation by PAR-1 and PAR-4 specific agonist peptides (SFLLRN and AYPGKF) did not reduce subsequent convulxin-insensitivity, as was observed with thrombin. (B) Vorapaxar, a PAR-1 antagonist, blocked thrombin-induced calcium signaling. (C) The convulxin-insensitivity after thrombin treatment was still apparent in the presence of vorapaxar. (PAR-1=SFLLRN activation peptide; PAR-4=AYPGKF activation peptide; V, vorapaxar; T, thrombin; C, convulxin).