| Abstract: | The incorporation and esterification by cultured human fibroblasts of vesicle- or low density lipoprotein-derived free 3H]cholesterol was examined. The rate of the cellular uptake of free 3H]cholesterol from lipid vesicles was similar in both LDL-receptor positive lung fibroblasts and in LDL-receptor negative fibroblasts. When human LDL was used as the carrier of free 3H]cholesterol, however, the LDL-receptor positive lung fibroblasts incorporated significantly more 3H]cholesterol than did the LDL-receptor negative cells. The exchangeable free 3H]cholesterol was available for intracellular esterification. The formation of 3H]cholesteryl esters was markedly inhibited by lysosomotropic drugs, either indicating a partly lysosomal esterification reaction, or implying that free 3H]cholesterol moves through the lysosomal compartment on its way to intracellular esterification sites. Either way, the lysosomes appear to have a metabolic role in the metabolism of exchangeable free 3H]cholesterol. |
