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

Abstract

Cells in tissue culture derive most of their lipids from the lipids present in the serum growth medium. Triglycerides are most rapidly utilized, but considerable quantities of cholesterol are also taken up. Some of the factors influencing cholesterol uptake by the MB III strain of mouse lymphoblasts were investigated. Cholesterol uptake was dependent upon the type of serum used in the growth medium. Cells grown on rabbit serum had a higher cholesterol content than those grown on human adult or human placental cord serum. Rabbit serum however had the lowest serum cholesterol level. Cholesterol content of cells was not influenced by the concentration of serum cholesterol provided that the relative proportions of cholesterol and serum protein were not changed. When emulsions of free (i. e. non-protein bound) cholesterol were added, relatively small increases in cholesterol content of the medium resulted in large increases in the content of cells. By use of C labelled cholesterol, it was shown that unbound cholesterol was taken up preferentially as compared to cholesterol in protein-bound form. Cells utilize both free and esterified serum cholesterol, but cell cholesterol is almost all in the unesterified form. 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.