Decreased accessibility of platelet-bound fibrinogen to antibody and enzyme
probes
EI Peerschke
Department of Pathology, SUNY, Stony Brook 11794.
The binding of fibrinogen to platelets is a multiphasic process leading to
apparently nonreversible associations between fibrinogen and stimulated
platelets. To further investigate changes in platelet- fibrinogen
interactions, the present study examined the accessibility of
platelet-bound fibrinogen and its GPIIb-IIIa receptor to antibody and
enzyme probes as a function of time after platelet stimulation with
adenosine diphosphate (ADP). Whereas only minimal changes in fibrinogen and
10E5 binding were observed within 60 minutes after platelet stimulation and
equilibrium fibrinogen binding, the binding of polyclonal antifibrinogen
antibodies decreased significantly (75% +/- 13%, mean +/- SD, n = 9).
Similar decreases were noted with rabbit antifibrinogen Fab and F(ab')2
fragments. In addition, plasmin (32 mU/mL) added to platelets five minutes
compared with 60 minutes after equilibrium fibrinogen binding dissociated
52% +/- 12% compared with 33% +/- 7% of platelet-bound fibrinogen in five
minutes, and 83% +/- 15% compared with 66% +/- 14% of bound fibrinogen in
15 minutes. No difference in plasmin cleavage products was observed,
however, by sodium dodecyl sulfate-polyacryl-amide gel electrophoresis
(SDS-PAGE). Complete fibrinogen dissociation occurred 30 minutes after
plasmin addition, confirming that fibrinogen was not internalized. In
contrast, dissociation of platelet-bound fibrinogen by chymotrypsin was
less affected by time after equilibrium fibrinogen binding, and minimal
changes in antifibrinogen antibody recognition and plasmin-induced
dissociation of fibrinogen bound to stimulated but glutaraldehyde-fixed
platelets were observed. The data suggest that ADP-induced fibrinogen
binding to fresh platelets is accompanied by progressive rearrangements of
fibrinogen on the platelet surface.
Volume 74,
Issue 2,
pp. 682-689,
08/01/1989
Copyright © 1989 by The American Society of Hematology