Interaction of free cholesterol and apoproteins of low and high density lipoproteins with isolated rabbit hepatocytes.

Primary cultures of rabbit hepatocytes were incubated with rabbit high density (HDL) and low density (LDL) lipoproteins in order to compare the surface transfer of free cholesterol with the uptake of apoproteins. Hepatocytes were maintained for various intervals with either LDL or HDL which contained both 125I-labeled protein and free [4-14C]cholesterol. After a 3-hr incubation with an LDL concentration equivalent to 25% of the normal rabbit serum level, the percentage of media 14C in hepatocytes was 2.3 times greater than the percentage of 125I; cells that had been incubated with HDL showed an eight-fold selectivity for 14C. Although the influx of free cholesterol from HDL was greater than that from LDL, there was no difference between the uptake of LDL protein and of HDL protein. The degradation of lipoproteins labeled with [3H]-leucine or 125I was compared. Hepatocytes incubated with lipoproteins labeled with [4-14C]cholesterol showed a greater influx of cholesterol from HDL2 than from LDL. The efflux of labeled cellular cholesterol was also greater to HDL2 than to LDL, whether the cellular cholesterol was labeled by prior exchange with labeled HDL2 or by endogenous synthesis of cholesterol from [2-3H]mevalonic acid lactone.