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EI Peerschke
Department of Pathology, State University of New York, Stony Brook 11794.
Previous studies indicated a correlation between the formation of EDTA-
resistant (irreversible) platelet-fibrinogen interactions and platelet
cytoskeleton formation. The present study explored the direct association
of membrane-bound fibrinogen with the Triton X-100 (Sigma Chemical Co, St
Louis, MO) insoluble cytoskeleton of aspirin-treated, gel-filtered
platelets, activated but not aggregated with 20 mumol/L adenosine
diphosphate (ADP) or 150 mU/mL human thrombin (THR) when bound fibrinogen
had become resistant to dissociation by EDTA. Conversion of exogenous
125I-fibrinogen to fibrin was prevented by adding Gly-Pro-Arg and
neutralizing THR with hirudin before initiating binding studies. After 60
minutes at 22 degrees C, the cytoskeleton of ADP-treated platelets
contained 20% +/- 12% (mean +/- SD, n = 14) of membrane-bound
125I-fibrinogen, representing 10% to 50% of EDTA- resistant fibrinogen
binding. The THR-activated cytoskeleton contained 45% +/- 15% of platelet
bound fibrinogen, comprising 80% to 100% of EDTA-resistant fibrinogen
binding. 125I-fibrinogen was not recovered with platelet cytoskeletons if
binding was inhibited by the RGDS peptide, excess unlabeled fibrinogen, or
disruption of the glycoprotein (GP) IIb-IIIa complex by EDTA-treatment.
Both development of EDTA- resistant fibrinogen binding and fibrinogen
association with the cytoskeleton were time dependent and reached maxima 45
to 60 minutes after fibrinogen binding to stimulated platelets. Although a
larger cytoskeleton formed after platelet stimulation with thrombin as
compared with ADP, no change in cytoskeleton composition was noted with
development of EDTA-resistant fibrinogen binding. Examination of platelet
cytoskeletons using monoclonal antibodies, sodium dodecyl
sulfate-polyacrylamide gel electrophoresis, and Western blotting showed the
presence of only traces of GP IIb-IIIa in the cytoskeletons of resting
platelets, with no detectable increases after platelet activation or
development of EDTA-resistant fibrinogen binding. These data suggest that
GP IIb-IIIa-mediated fibrinogen binding to activated platelets is
accompanied by time-dependent alterations in platelet- fibrinogen
interactions leading to the GP IIb-IIIa independent association between
bound fibrinogen and the platelet cytoskeleton.
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| Copyright © 1991 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||