Lipid Metabolism in Cultured Cells. I. Factors Affecting Cholesterol Uptake. ∗

Abstract

Summary

1. Some of the factors influencing uptake of cholesterol by a strain of mammalian cells growing in vitro have been examined. 2. Cholesterol uptake by cells is dependent upon the type of serum used in the medium. Cells grown on rabbit serum had a higher cholesterol content than cells grown on human adult serum or human placental cord serum. Rabbit serum, however, had the lowest serum cholesterol level. 3. Cholesterol content of cells was not influenced by concentration of serum cholesterol in the growth medium provided the relative proportions of cholesterol and serum protein were not changed. 4. When emulsions of free (nonprotein bound) cholesterol were added to serum medium, relatively small increases in cholesterol content of the medium resulted in large increases in cholesterol content of the cells. 5. By use of C¹⁴ labelled cholesterol, it was shown that unbound cholesterol was taken up preferentially as compared with cholesterol in the protein-bound form. 6. Cholesterol content of cells was not influenced by addition of stearic acid or linoleic acid to the growth medium. 7. Cells utilized both free and esterified serum cholesterol. The ester was apparently hydrolyzed intracellularly since the cell cholesterol was almost entirely in the unesterified form. 8. It is concluded that the main factor controlling cellular cholesterol uptake may be the relationship between serum cholesterol and the binding power of the serum proteins, rather than the cholesterol level itself.