Modulation of cytoplasmic cholesteryl ester of smooth muscle cells in culture derived from rat, rabbit and bovine aorta.

Esterification of cholesterol in smooth muscle cells, isolated from rat, rabbit and bovine aorta, was achieved by incubation with cholesterol enriched medium containing [7(n)-3H]cholesterol. The newly formed cholesteryl ester was readily hydrolyzed when the cells were post-incubated with medium containing lipoprotein deficient serum. The rate of loss of labeled cholesteryl ester was not inhibited by the presence of 100 microM chloroquine. Addition of LDL to the post-incubation medium retarded the decrease in labeled cellular cholesteryl ester in rat smooth muscle cells and this effect of LDL was abolished by chloroquine. In bovine and rabbit smooth muscle cells, enriched in cholesteryl ester, addition of LDL to post-incubation medium resulted in an increase in labeled cholesteryl ester and in cholesteryl ester mass. Retardation in the loss of labeled cellular cholesteryl ester occurred also on addition of oleic acid to the post-incubation medium. In the presence of HDL and especially of high density apolipoprotein-sphingomyelin liposomes there was an efflux of cellular free cholesterol and a reduction in cholesteryl ester. These findings indicate that the catabolism of cytoplasmic cholesteryl ester in aortic smooth muscle cells is catalyzed by extralysosomal enzymes. The cytoplasmic cholesteryl ester hydrolase is apparently not activated by cyclic AMP. The intracellular availability of unesterified cholesterol, which can be modulated by plasma lipoproteins, may determine the residence time of cellular cholesteryl ester. Thus under pathological conditions an increase in extracellular LDL accompanied by a reduction in HDL would prolong the residence time of cholesteryl esters and thus promote their intracellular accretion.