Utilization of Serum Lipids by Cultured Mammalian Cells.

Summary 1) A variety of mammalian cells growing in tissue culture took up appreciable amounts of lipid from the serum used in the medium. For the MB III strain of mouse lymphoblasts, triglycerides were most rapidly utilized followed by phospholipids and thea cholesterol. This preferential utilization of triglycerides was also shown by 4 other cell strains. 2) The MB III cell utilized saturated and unsaturated lipids equally readily, and there was little net breakdown of lipid to satisfy cell energy requirements. There was however considerable conversion of triglycerides to phospholipid following absorption. 3) Cholesterol uptake appears to be a general phenomenon, and appreciable amounts ranging from 0.6% to 2.8% of the dry weight were found in all strains of cultured cells examined. Cholesterol content of cells was related to the type of serum used in the growth medium. 4) The composition of the lipid taken up by the cells differed markedly from that in the medium. This is discussed from the point of view of: (1). A specific process of uptake or (2). A non-specific uptake by pinocytosis, followed by incorporation and a non-specific excretion. Evidence is presented in favor of this second mechanism.