Active-site-dependent, thrombin-induced release of adenine nucleotides from cultured human endothelial cells

The effect of thrombin on release of adenine nucleotides is studied in cultured cell monolayers from the human umbilical vein. Thrombin-induced release of radioactivity from endothelial cells is dose-dependent and saturable with maximal response seen at 1 x 10(-8) M thrombin. The products are identified by thin-layer chromatography as adenine nucleotides. Diisopropylphosphoryl thrombin, which is enzymatically inactive, does not cause release of tritium. A 50-fold excess of diisopropylphosphoryl-thrombin, despite causing 98 percent inhibition of binding of 125I-thrombin to its high-affinity binding sites, does not inhibit thrombin-induced release. We conclude that (1) thrombin causes release from endothelial cells of adenine nucleotides and that (2) high-affinity, active-site-independent binding of thrombin is not involved in this process.