Uptake of rat plasma HDL subfractions labeled with [ 3H]cholesteryl linoleyl ether or with 125I by cultured rat hepatocytes and adrenal cells

Abstract

Rat plasma low- and high-density lipoproteins were labeled with [ 3H]cholesteryl linoleyl ether and isolated by rate-zonal ultracentrifugation into apolipoprotein B-containing LDL, apolipoprotein E-containing HDL 1 and apolipoprotein E-poor HDL 2. These fractions were incubated with cultured rat hepatocytes comparable amounts of all lipoproteins were taken up by the cells. Rat HDL was isolated at d 1.085–1.21 g/ml and apolipoprotein E-free HDL was prepared by heparin Sepharose chromatography. The originai HDL and the apolipoprotein E-free HDL were labeled with 125I or with [ 3H]cholesteryl linoleyl ether and incubated with rat hepatocytes or adrenal cells in culture. The uptake of apolipoprotein E-free [ 3H]cholesterol linoleyl ether HDL by the cultured hepatocytes was 20–40% more than that of the original HDL. Comparison of uptake of cholesteryl ester moiety (represented by uptake of [ 3H]cholesteryl linoleyl ether) and of protein moiety (represented by metabolism of 125I-labeled protein) was carried out using both original and apolipoprotein E-free HDL. In experiments in which low concentrations of HDL were used, the ratio of 3H/ 125I exceeded 1.0. In cultured adrenal cells, the uptake of [ 3H]cholesteryl linoleyl ether-labeled HDL was stimulated 3–6-fold by 1 · 10 −7 M ACTH, while the uptake of 125I-labeled HDL increased about 2-fold. The ratio of 3H/ 125I representing cellular uptake was 2–3 and increased to 5 in ACTH-treated cells. The present results indicate that in cultured rat hepatocytes the uptake of homologous HDL does not depend on the presence of apolipoprotein E. Evidence was also presented for an uptake of cholesteryl ester independent of protein uptake in cultured rat adrenal cells and to a lesser extent in rat hepatocytes.