Metabolism of low density lipoprotein by bovine endothelial cells as a function of cell density.

The amount of low density lipoprotein (LDL) bound to the LDL receptor of bovine aortic endothelial cells at widely varying cell densities was measured by two methods: the commonly used dextran-sulfate-release method after LDL binding at 0-4 degrees C, and the method of assay of the LDL internalized in 30 minutes at 37 degrees C after LDL binding at 0-4 degrees C. Values obtained for LDL binding by the two methods were similar. At cell densities ranging from very sparse (6 X 10(3) to very dense (greater than 10(6) cells/cm2), both binding and degradation of 125I-LDL decreased in a nonlinear but parallel manner as cell density increased. This change began to occur at subconfluent densities and appeared to be not simply the result of establishment of a confluent cell layer. Thus, endothelial cells respond to changes in cell density with reciprocal changes in LDL metabolism in the same manner as reported for fibroblasts, so that at confluency both LDL receptor activity and LDL degradation are very low.