Different role of platelet glycoprotein GP Ia/IIa in platelet contact and activation induced by type I and type III collagens

The role of glycoprotein Ia/IIa was studied during platelet contact and agg regation induced by type I and type III collagen. The anti-glycoprotein Ia/ IIa (6F1) antibody inhibited type I collagen-induced aggregation but did no t inhibit the first contact between platelets and collagen. In contrast, it was without effect either on type III collagen-induced contact or platelet interaction with the subendothelium in a static assay. Platelet aggregatio n induced by type III collagen was only slightly slowed down by 6F1 but pp7 2 spleen tyrosine kinase phosphorylation was not modified even at concentra tions of 6F1 that completely blocked platelet activation induced by type I collagen. Our results indicate that glycoprotein Ia/IIa is not a primary bi nding site for type I or type III collagen on the platelet membrane. This r eceptor is more specifically involved in type I collagen-induced platelet s preading and aggregation. (C) 2000 Elsevier Science Ltd. All rights reserve d.