The glycoprotein IIb-IIIa complex may be directly involved in collagen-induced platelet aggregation, expanding its known role beyond being a fibrinogen receptor.
Two recently developed membrane-impermeant cross-linkers, 3,3'-dithiobis(sulfosuccinimidyl propionate) (DTSSP) and bis(sulfosuccinimidyl) suberate (BS3), have been used to examine the interaction of human platelets with collagen. Reaction of human platelets with either of the two cross-linking reagents at micromolar concentrations completely inhibited platelet aggregation in response to collagen but not in response to thrombin. Platelet adhesion to collagen was, however, not affected by these reagents. Inhibition of collagen-induced platelet aggregation by DTSSP or BS3 appears to be due to cross-linking and not simply to the chemical modification of membrane proteins, since the homologous monofunctional reagent sulfosuccinimidyl propionate had no effect on platelet aggregation. Inhibition of platelet aggregation by BS3 was accompanied by a decrease in the intensity of glycoprotein bands IIb, IIIa, and IV when analyzed on sodium dodecyl sulfate (NaDodSO4)-polyacrylamide gels. In order to determine if collagen is directly interacting with a specific platelet membrane glycoprotein, 3H-labeled platelets were allowed to adhere to collagen and then cross-linked with various concentrations of DTSSP. Proteins which remain associated with collagen after lysis and washing were analyzed on NaDodSO4 gels. At concentrations of 16-50 microM DTSSP, glycoproteins IIb and IIIa appeared to be specifically cross-linked to collagen. These results suggest that the glycoprotein IIb-IIIa complex, which has previously been implicated as the fibrinogen receptor in activated platelets, may also be directly involved in collagen-induced platelet aggregation.
Kotite et al. (Tue,) studied this question.