Evidence that the effects of thrombin on arachidonate metabolism in cultured human endothelial cells are not mediated by a high affinity receptor.

The effect of thrombin and its derivative, diisopropylphosphoryl-thrombin on [3H]arachidonic acid metabolism is studied in cultured umbilical vein endothelial cell monolayers. Thrombin causes a dose-dependent release of radioactivity from endothelial cells fed [3H]arachidonate. Thin layer radiochromatography of acidified supernatants reveals that most of the radio-activity is [3H]arachidonate and its metabolites, 6-ketoprostaglandin F1 alpha and prostaglandin E2. Diisopropylphosphoryl-thrombin, which is enzymatically inactive, does not cause release of arachidonic acid or metabolites. A 50-fold excess of diisopropylphosphoryl-thrombin, despite causing 98% inhibition of binding of 125I-thrombin to its high affinity binding sites, does not inhibit thrombin-induced release. We conclude that the high affinity, active site-independent thrombin binding sites are not involved in thrombin-induced mobilization of esterified arachidonic acid.