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L Liu and GM Rodgers
Department of Medicine, Veterans Affairs Medical Center, Salt Lake City,
UT, USA.
In vivo prothrombin activation is thought to occur via a factor Xa/factor
V-dependent mechanism. We investigated whether human venous endothelial
cells (EC) could be induced to express a prothrombin activator. EC treated
with lipopolysaccharide (LPS) or interleukin-1 activated prothrombin in the
absence of exogenous factors Xa and V. This activity resided in the
membrane fraction of EC and was not inhibited by an antibody to factor V.
The apparent Km value was 3.3 +/- 0.3 mumol/L. Comparative studies of
thrombin generation using a model system of phospholipid and factors Xa/V
versus LPS-treated EC were performed to quantitate the effects of known
inhibitors to factor Xa. The factor Xa inhibitor DEGR-chloromethyl ketone
and an antibody to factor X inhibited prothrombin activation. However, the
EC activator did not hydrolyze a factor Xa chromogenic substrate, and
recombinant tick anticoagulant peptide did not suppress activity of the
prothrombin activator. The apparent molecular weight of the EC activator
was approximately 30 kD. Exogenous factor V enhanced the activity of the EC
activator, such that in the presence of factor V, the apparent K(m) value
was 1.28 +/- 0.10 mumol/L. Additionally, LPS-treated EC activated exogenous
factor V. This activator has several characteristics of a previously
described inducible murine monocyte prothrombin activator and may
contribute to thrombin generation associated with pathologic stimuli.
This article has been cited by other articles:
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| Copyright © 1996 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||
