ROLE OF DELTA-9 DESATURASE ACTIVITY IN THE MAINTENANCE OF HIGH-LEVELSOF MONOENOIC FATTY-ACIDS IN HEPATOMA CULTURED-CELLS

The incorporation and Delta 9 desaturation of exogenous [C-14]stearic acid were studied in HTC 7288c cells in suspension. We examined the up take of the acid over a wide range of concentrations (0-160 mu M) afte r incubating the cells for 6 h in a chemically-defined medium. Under t his experimental condition, the uptake of the labeled acid was more ex tensive than that obtained from static cultures or from monolayer of i solated hepatocytes of rats. At an external concentration of 160 mu M ca. 52 nmoles of acid per mg of cellular protein was taken up. The pro duction of oleic acid from [C-14]stearate (Delta 9 desaturation) corre lated well with the uptake curve between 0-80 mu M concentration. For higher stearate concentrations, the biosynthesis of oleic acid decline d substantially and a plateau of 22 nmoles/mg cellular protein was rea ched. The incorporation and desaturation of an initial exogeneous conc entration of [C-14]stearic acid (80 mu M) was also studied from 0-6 h. The results obtained demonstrated that the uptake of the substrate in to cellular lipids was fast and non saturable. Quantitative gas-liquid chromatography of total cellular lipids under the different experimen tal conditions demonstrated a negative correlation between the decreas e in the palmitic and palmitoleic acids and the increase in the intrac ellular levels of stearic and oleic acids. These analytical modificati ons took place with no changes in the saturated/monoenoic fatty acid r atio. This work also demonstrated a significant contribution of the st earoyl-Coa desaturase system to the high levels of oleic acid present in this kind of hepatoma cells.