ANTIBODIES TO PROTEASE-ACTIVATED RECEPTOR-3 INHIBIT ACTIVATION OF MOUSE PLATELETS BY THROMBIN

Recent studies of mice deficient in the thrombin receptor, protease-ac tivated receptor 1 (PAR1), provided definitive evidence for the existe nce of a second thrombin receptor in mouse platelets, We recently iden tified a new thrombin receptor designated protease-activated receptor 3 (PAR3). The mRNA encoding a mouse homologue of PAR3 was highly expre ssed in mouse splenic megakaryocytes, making it a good candidate for t he missing mouse platelet thrombin receptor. We now report that PAR3 p rotein is expressed on the surface of mouse platelets and that PAR3 an tibodies partially inhibit activation of mouse platelets by thrombin b ut not U46619, a thromboxane receptor agonist, These observations sugg est that PAR3 contributes to mouse platelet activation by thrombin. (C ) 1998 by The American Society of Hematology.