Receptors for high molecular weight kininogen on stimulated washed human platelets

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Abstract
Binding of human high molecular weight kininogen (HMK) to washed human platelets was studied by measuring platelet-associated radiolabeled ligand in pellets of centrifuged platelets. HMK was bound to stimulated platelets in the presence of ZnCl2 in a specific and saturable manner. Ca2+ potentiated ligand binding but did not substitute for Zn2+. Optimal binding of HMK occurred near the plasma concentrations of both Zn2+ and Ca2+. Scatchard analysis yielded 24,200 binding sites for HMK with an apparent dissociation constant of 20 nM. These studies show that stimulated human platelets can bind many HMK molecules with high affinity and suggest that the platelet surface may potentially serve as an important site for localizing the initial reactions of the plasma kinin-forming and intrinsic coagulation pathways.