AJP - Endocrinology and Metabolism, Vol 261, Issue 1 E76-E86, Copyright © 1991 by American Physiological Society
Metabolism of oleic acid in differentiating BFC-1 preadipose cells
N. A. Abumrad, C. Forest, D. M. Regen, U. S. Barnella and S. A. Melki
Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Incorporation of [3H]oleate and [14C]glucose into cellular lipids was
studied in the preadipose cell line BFC-1 to determine flux changes that
accompany the adipose conversion process. Dilution of oleate by
intracellular fatty acids (FA) was estimated from the 3H/14C incorporation
ratios and from relating steady-state radioactivity in diglycerides to
their measured cellular levels. The data indicated that exogenous FA mixed
with less than 1% of endogenous FA on its pathway to esterification.
Conversion of preadipocytes to adipocytes increased uptake of FA and
glucose by approximately 3-fold and synthesis of diglycerides and
triglycerides by 5- and 16-fold, respectively, with little if any increase
of phospholipid synthesis. A 50% drop in 3H/14C incorporation ratio
indicated a doubling of the rate at which endogenous FA mixed with the
exogenous FA that had entered the cell. Adipocytes compared with
preadipocytes exhibited a 50% greater cell diameter and a doubling of
intracellular water volume and of protein and phospholipid levels,
reflecting cellular enlargement consequent to the arrest of cell division
that precedes adipose conversion. Diglyceride levels were also increased in
adipocytes, however, since their turnover was fast, as indicated by rapid
equilibration of diglyceride labeling; the increase reflected changes in
their relative rates of synthesis and disposal. Diglyceride levels related
to cell phospholipid, and other indexes of cell size remained constant.
This indicated that the supply of diglycerides was tightly coupled to the
synthesis of triglycerides and phospholipids, which suggested feedback
regulation of diglyceride formation. The studies provide a methodological
approach to measurement and interpretation of rates of lipid deposition in
cultured cells.
