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The kinetics of low density lipoprotein (LDL) cholesterol transport to the plasma membrane of Chinese hamster ovary (CHO) cells was studied. LDL was reconstituted with 3Hcholesteryl linoleate and added to CHO cells in a pulse-chase experiment. The internalization and lysosomal cleavage of reconstituted LDL (rLDL) 3Hcholesteryl linoleate to free 3Hcholesterol occurred with a half-time of 37 min after a 30-min lag. The rate of transport of released 3Hcholesterol to the plasma membrane was measured by brief (20-30 sec) cholesterol oxidase treatment of intact, adherent cells: the half-time of transport was 42 min. The similarity in the rate of free cholesterol release from rLDL and transport of this cholesterol to the plasma membrane suggests very rapid transport of rLDL cholesterol from the lysosome to the plasma membrane. Cells were shown to be intact throughout the cholesterol oxidase treatment by the absence of cell-derived lactate dehydrogenase (LDH) activity or K+ in the assay buffer.
Brasaemle et al. (1990) studied this question.