Phospholipase abolishes the effect of stimulated platelets on the thrombin
activation of factor VIII
ME Rick and DM Krizek
Clinical Pathology Department, National Institutes of Health, Bethesda, MD
20892.
Factor VIII functions as a cofactor in the intrinsic coagulation pathway
and must first be activated to function optimally in this capacity. Low
concentrations of thrombin activate factor VIII, and the presence of
stimulated platelets is known to enhance the activation of factor VIII
complexed to von Willebrand factor. The current studies show that platelets
stimulated by thrombin, collagen, or calcium ionophore will increase the
activation of isolated factor VIII by thrombin. Ongoing platelet release is
not necessary for the enhanced factor VIII activation, nor is platelet von
Willebrand factor or platelet membrane glycoproteins Ib or IIb/IIIa.
Platelet membrane phospholipids, on the other hand, are important for the
enhanced activation of factor VIII by thrombin because the effect of
stimulated platelets is abolished by incubation of the stimulated platelets
with phospholipases. These results suggest that the enhanced activation of
factor VIII by thrombin in the presence of stimulated platelets may be
mediated by factor VIII binding to platelet phospholipid or to a receptor
whose functional integrity is dependent on surrounding membrane
phospholipid.
Volume 71,
Issue 1,
pp. 173-177,
01/01/1988
Copyright © 1988 by The American Society of Hematology
