Binding of tissue plasminogen activator to human umbilical vein endothelial cells.

Binding of purified recombinant human tissue plasminogen activator to cultures of human umbilical vein endothelial cells (HUVEC) was studied in vitro. 125I-tPA was shown to bind to HUVEC in a specific, saturable, and dissociable manner. Scatchard analysis revealed a low affinity binding site with Keq = 4.2 X 10(6) M-1 and 1.2 X 10(7) sites per cell. Binding of tPA was inhibited by L-lysine, e-aminocaproic acid, and D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone but not by carbohydrates including mannose, galactose, N-acetyl glucosamine and N-acetyl galactosamine. Neat human plasma abrogates but does not totally inhibit binding of tPA to HUVEC. These results may indicate a role for endothelial cells in the removal of tPA from the circulation in vivo.