Binding, internalization and degradation of heparin and heparin fragments by cultured endothelial cells.

We have studied the binding to bovine adrenal capillary endothelial cells cultured in vitro of heparin from different sources (porcine heparin Ep. 152 P, Av.M.W. 15.9 Kd and bovine heparin Ep. 756 P, Av.M.W. 12.9 Kd) and heparin fractions of various molecular weights (low molecular weight heparin, LMW 2123 OP, Av.M.W. 4.5 Kd and very low molecular weight heparin, VLMW 1027/45 OP Av.M.W. 2.1 Kd). The binding was specific for heparin; heparan sulphate showed some competition whereas dextran sulphate and glycosaminoglycans did not. We determined the affinity of heparin and heparin fragments for endothelial cells by means of displacement of bound 3H-labeled heparin in response to increasing concentration of unlabeled compounds. The binding of the different heparin fractions depends on their molecular weights. VLMW 1027/45 OP was unable to bind to the cells, whereas LMW 2123 OP showed an affinity 10 times lower then porcine heparin. Bovine adrenal capillary endothelial cells incubated with unfractionated 3H-labeled heparin selectively bound internalized and degraded high molecular weight heparin fractions, as shown by gel filtration of the 3H-labeled heparin both after binding to the cells and after internalization.