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K Varadi and S Elodi
The formation and functioning of the factor X activating complex on the
surface of cultured human venous endothelial cells (HVEC) were
investigated. To the HVEC monolayer human factors IXa, VIII, X, CaCl2, and
S-2222 were added, and a gradually increasing activation of factor X was
observed. The maximum activity of 88 nmol/L Xa/min was reached after a
12-minute lag phase. In the presence of thrombin-activated factor VIII
(VIIIt) the same maximum activity developed in eight minutes, which
suggests that VIIIt accelerates the formation of the IXa- VIII complex but
does not influence its factor X-activating potential. Anti-VIII IgG did not
affect the activity of the full-fledged complex. When anti-VIII IgG was
added to the reaction mixture before factor VIII or during the lag phase of
the reaction, it induced a concentration- dependent decrease of factor X
activation. These results indicate that endothelial cells provide a binding
surface for the IXa-VIII complex and that in the HVEC-bound complex factor
VIII is protected from the effect of a specific antibody. However, the
relatively slow development of the maximum activity indicates that HVEC
only partially satisfy the surface criteria for the optimal assembly of the
IXa-VIII complex.
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| Copyright © 1987 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||
