ANTITHROMBIN BINDING BY HUMAN UMBILICAL VEIN ENDOTHELIAL-CELLS - EFFECTS OF EXOGENOUS HEPARIN

Human umbilical vein endothelial cells cultured in growth media that d id not contain exogenous heparin were found to grow less well while bi nding significantly more antithrombin (AT) than comparable cells cultu red in growth media that did contain exogenous heparin (90 mu g/ml). T he binding of AT to plasma membranes of cultured endothelial cells was measured immunologically by flow cytometry. This binding was eliminat ed completely by reacting the cells with heparinase III before incubat ing them with AT, indicating that the most likely heparinase-sensitive process responsible for AT binding to plasma membranes was heparan su lfate 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 bindin g were found to be dependent on their sulfation. Thus, one response of endothelial cells to heparin deficiency is up-regulation of the abili ty to bind AT to plasma membranes.