Antithrombin binding by human umbilical vein endothelial cells: effects of exogenous heparin

Human umbilical vein endothelial cells cultured in growth media that did not contain exogenous heparin were found to grow less well while binding significantly more antithrombin (AT) than comparable cells cultured in growth media that did contain exogenous heparin (90 micrograms/ml). The binding of AT to plasma membranes of cultured endothelial cells was measured immunologically by flow cytometry. This binding was eliminated completely by reacting the cells with heparinase III before incubating them with AT, indicating that the most likely heparinase-sensitive process responsible for AT binding to plasma membranes was heparan sulfate proteoglycan. Increased AT binding also was promoted by addition of heparin-binding molecules (protamine, AT, or ECGF) to growth media, and the effects of other glycosaminoglycans and dextran on AT binding were found to be dependent on their sulfation. Thus, one response of endothelial cells to heparin deficiency is up-regulation of the ability to bind AT to plasma membranes.