Convulxin-induced platelet adhesion and aggregation: involvement of glycoproteins VI and IaIIa.

The interaction of convulxin (Cvx), a 72-kDa glycoprotein isolated from the venom of Crotalus durissus terrificus with human platelets has been studied. Cvx at low concentrations (below 100 pM) induced platelet aggregation, dense body secretion and intracellular calcium mobilization which indicates that Cvx is a potent activator of human platelets. Cvx-induced platelet aggregation and secretion was inhibited by 6Fl an anti-integrin alpha2beta1 monoclonal antibody that was without effect on calcium mobilization. Anti-GPVI Fab fragments inhibited aggregation, secretion and calcium mobilization triggered by Cvx. In addition, immobilized Cvx was found to induce divalent cation-independent platelet adhesion in a static system. Platelet adhesion to Cvx was inhibited by anti-GPVI Fab fragments but not by anti-integrin alpha2beta1 . Cvx was shown to bind to a 57,000 Dalton protein that was identified as GPVI. Altogether, these results indicate that GPVI behaves as a receptor for Cvx, while integrin alpha2beta1 could play a regulatory role in Cvx-induced platelet aggregation. Cvx and collagen interaction with platelets, thus appears to share some characteristics but to also have specific properties.