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N Yamamoto, H Kitagawa, K Yamamoto, K Tanoue and H Yamazaki
Department of Cardiovascular Research, Tokyo Metropolitan Institute of
Medical Science, Japan.
Using a newly developed murine monoclonal antibody (MoAb), TM83, against
glycoprotein IIIa (GPIIIa) of human platelets, we have analyzed the
relationship between platelet fibrinogen binding and conformational changes
in GPIIIa under EDTA treatment. Crossed radioimmunoelectrophoresis
demonstrated that TM83 reacted with only the GPIIb/IIIa complex but also
with GPIIIa alone. TM83 dose-dependently inhibited both thrombin-induced
aggregation and fibrinogen binding to activated platelets. 125I-TM83 bound
to an average of 20,890 +/- 1,600 (mean +/- SE, n = 12) sites on a resting
platelet, with Kd = 2.06 nmol/L in the presence of Ca2+. When platelets
were incubated in 2 nmol/L EDTA-containing medium, pH 7.4, at 22 degrees C
for 30 minutes, binding of TM83 decreased to 70% of the control level. The
decreased binding was fully recovered to the control level when the
platelets were resuspended in Ca2+-containing medium. These platelets
retained their aggregability. In contrast, when platelets were incubated in
2 mmol/L EDTA-containing medium, pH 7.4, at 37 degrees C for 30 minutes,
TM83 binding to the platelets markedly decreased to 7% of the control,
which could only be recovered to 40% of the control by replacing the medium
with calcium-containing medium; these platelets lacked thrombin- induced
aggregability. These findings suggest that the epitope for TM83 may be
located near the fibrinogen binding site on GPIIIa and that its
conformation is dependent on Ca2+ ions.
This article has been cited by other articles:
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| Copyright © 1989 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||
