Dependence of plasmin-mediated degradation of platelet adhesive receptors
on temperature and Ca2+
KJ Winters, PR Eisenberg, AS Jaffe and SA Santoro
Cardiovascular Division, Washington University School of Medicine, St Louis
MO 63110.
The effects of activation of plasminogen by streptokinase and tissue-
type-plasminogen activator on platelet activation and the membrane
glycoproteins (GPs) that mediate platelet adhesion and aggregation are not
yet fully defined. To clarify effects on platelets during activation of
plasminogen in vitro, we used monoclonal antibodies (MoAbs), flow
cytometry, and platelets surface-labeled with 125I to characterize changes
in receptors for fibrinogen (GPIIb-IIIa), von Willebrand factor (GPIb), and
collagen (GPIa-IIa). Activation of plasminogen in plasma with pharmacologic
concentrations of plasminogen activators did not degrade GPIIb-IIIa or
GPIb, and caused only a modest decrease in GPIa. In washed platelets
GPIIb-IIIa was extensively degraded by plasmin at 37 degrees C in the
absence of exogenous Ca2+, conditions that destabilize the IIb-IIIa
complex. Degradation of GPIb in washed platelets displayed a similar
although less-marked dependence on temperature and the absence of Ca2+. The
binding of activation- specific MoAbs did not increase during activation of
plasminogen in plasma. We conclude that during pharmacologic fibrinolysis,
reported inhibition of platelet function in plasma is not due to
degradation of platelet-adhesive receptors. In addition, platelet
activation observed during thrombolytic therapy does not appear to be a
direct consequence of plasminogen activation.
Volume 76,
Issue 8,
pp. 1546-1557,
10/15/1990
Copyright © 1990 by The American Society of Hematology
