Initiation of Platelet Adhesion by Arrest onto Fibrinogen or Translocation on von Willebrand Factor

Abstract

We have identified two distinct mechanisms initiating the adhesion of flowing platelets to thrombogenic surfaces. The integrin α IIbβ 3 promotes immediate arrest onto fibrinogen but is fully efficient only at wall shear rates below 600–900 s −1, perhaps because of a relatively slow rate of bond formation or low resistance to tensile stress. In contrast, glycoprotein Ibα binding to immobilized von Willebrand factor (vWF) appears to have fast association and dissociation rates as well as high resistance to tensile stress, supporting slow movement of platelets in continuous contact with the surface even at shear rates in excess of 6000 s −1. This eventually allows activated α IIbβ 3 to arrest platelets onto vWF under conditions not permissive of direct binding to fibrinogen. The coupling of these different functions may be crucial for thrombogenesis.