Exposure of a Human Platelet Fibrinogen Receptor by ADP

J. S. Bennett, G. Vilatre
1979 VIIth International Congress on Thrombosis and Haemostasis   unpublished
Fibrinosen is a cofactor for the aggregation of human platelets by ADP but its precise role is not known. In order to clarify the function of fibrinogen in platelet aggregation, we measured the binding of 125I-labeled human fibrinogen to gel-filtered human platelets before and after platelet emulation by ADP. Incubations were performed without stirring to prevent platelet aggregation and secretion. Platelet-bound and free 125I-fibrinogen were separated by centrifugaron of the platelets through
more » ... ilicone oil. Specific fibrinogen binding was that ibrinogen which could be displaced from the platelets by a 10-fold excess unlabeled fibrinogen. Specific fibrinogen binding required platelet stimulation by ADP and either Ca+2 or Mg+2. Specific ending reached equilibrium within 60 sec. Demonstrated saturation kinetics, and did not occur with thrombasthenic platelets. Scatchard analysis demonstrated a single class of ending sites with a Kd of 25 ± 3.9 ug/ml and 39,000 ± 5,000 binding sites per platlet the extent of ADP-induced fibrinogen binding to unstirred platelets was compared to the extent of aggregation of stirred platelets induced by the same concentrations of ADP, correlation 0.96 was seen. This study demonstrates. that a uniform population of fibrinogen receptors is exposed on the platelet surface by ADP. Furthermore, we suggest that the fibrinogen molecules bound to the platelet as a result of ADP stimulation are directly involved in the platelet aggregation response.
doi:10.1055/s-0039-1687386 fatcat:anlccsdopjblrnlfw5dzcmzufe