Summary
Cultured human umbilical vein endothelial cells responded to thrombin (10−2 – 10 NIH u/ml) with a 2-5 fold increase in thromboplastin activity. The maximum response
was reached after 4 hr in serum-free medium. The effect of thrombin was fully inhibited
by the presence of 50% (v/v) fetal calf serum or more in the medium, by preincubation
of thrombin with hirudin or by treatment of thrombin with N-bromosuccinimide or phenylmethylsulfonyl
fluoride. The thrombin-induced thromboplastin activity was inhibited by incubation
of the cells with cycloheximide (2 μg/ml) or actinomycin D (2 μg/ml) showing that
the response depended on de novo protein and RNA synthesis. It was also suppressed
by exposure of the cells to two different phosphodiesterase inhibitors, 3-butyl-l-methyl-xanthine
(5 · 10−4 M) and rac-4 (3-butoxy-4-methoxybenzyl)-2-imidazole (5 · 10−4 M), to the transmethylation inhibitors 3-deazaadenosine (10−5 M) and 1-homocysteine thiolactone (2 · 10−5 M) in combination and to the intracellular calcium antagonist 8-(N,N-diethylamino)-octyl
3,4,5,-tri-methoxybenzoate hydrochloride (8 · 10−5 M). Our results suggest that small amounts of thrombin can induce thromboplastin
synthesis in endothelial cells in vitro and that this synthesis probably is regulated
by the intracellular level of cAMP, by cytoplasmic Ca2+ and possibly also by transmethylation reactions.
Keywords
Endothelial cells - Thrombin - Thromboplastin
