Glycocalicin binding to von Willebrand factor adsorbed onto collagen-coated or polystyrene surfaces

In order to analyze the interaction of platelets with von Willebrand factor (vWF) and collagen, we studied the binding of glycocalicin (GC) and formalin-fixed platelets to vWF adsorbed onto uncoated or collagen-coated polystyrene surfaces. These studies show that three-fold more vWF binds to collagen-coated polystyrene than to polystyrene coated with fibrin monomer or fibrinogen. At saturation, 37 +/- 2.9 ng vWF bound to the collagen-coated wells, compared to 12.8 +/- 5.4 ng, and 10.9 +/- 2.7 ng of vWF bound to wells coated with fibrin monomer and fibrinogen, respectively. GC also bound significantly more to collagen-coated wells than to wells coated with fibrinogen, and this binding was increased approximately two-fold (from 7 +/- 0.65 ng to 14 +/- 1.1 ng) in the presence of vWF adsorbed to the collagen-coated surface. Only 2 ng of GC was bound to 3000 ng of vWF when the latter was adsorbed directly onto a polystyrene surface. In contrast, GC binding to vWF adsorbed onto a collagen-coated surface was enhanced 600-fold with 7.0 ng of GC bound to 18 ng of immobilized vWF. Formalin-fixed platelets showed little binding to vWF adsorbed onto the microtiter wells. At saturation, 7 x 10(4) platelets bound to 3000 ng of vWF; a 6-fold increase in platelet binding was observed using collagen-coated wells and this binding was increased even further in the presence of vWF, resulting in 250-fold increase in platelet binding to vWF when the latter was adsorbed onto a collagen surface. These studies suggest that (1) GC is involved in platelet binding to collagen and this binding is increased by vWF; (2) GC binding to vWF is enhanced by the collagen-coated surface; (3) the adsorption of vWF onto a collagen surface may induce conformational changes in vWF that promote its interaction with GC or glycoprotein Ib.