Low density lipoprotein metabolism by endothelial cells from human umbilical cord arteries and veins.

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Abstract
Binding and metabolism of low density lipoprotein (LDL) and acetylated LDL were examined in endothelial cells from human umbilical cord arteries and veins. Both high and low affinity LDL interactions were observed. High affinity LDL binding and catabolism were increased five- to sevenfold after preincubation for 18 hours in LPDS containing medium. Subconfluent cells degraded, endocytosed, and bound 1.5 to 2.7 times more LDL by high affinity interaction than confluent cells, when endothelial cell growth supplement (ECGS) was present in the culture system. In the absence of ECGS, these ratios were somewhat less. Low affinity LDL metabolism was less affected by the state of confluency. Binding of LDL and acetylated LDL by venous endothelial cells was more than two- and threefold, respectively, than that by comparable arterial cells. However, the difference in LDL binding was not reflected in an altered LDL catabolism. There apparently is a population of low affinity binding sites not involved in LDL catabolism. LDL metabolism was identical in cells, which were cultured in medium supplemented with 20% to 100% serum or hirudin- or heparin-treated platelet-poor plasma. Without preincubation in LPDS, high affinity adsorptive endocytosis mediated the main part of LDL uptake only at low LDL concentrations (5 to 20 micrograms protein/ml). However, at physiological LDL concentrations (550 micrograms/ml), we estimated that this process mediated only 17% of the LDL uptake. We calculated that fluid endocytosis and low affinity adsorptive endocytosis of LDL accounted for the remaining 12% and 70%, respectively, of the LDL uptake at physiological LDL concentrations.

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