Development of a system to examine the regulation of triglyceride accumulation and mobilization in isolated hepatocytes

The first aim was to induce varying levels of incorporation of [3H]-palmitate (P) in triglyceride (TG), phospholipid (PL), and cholesteryl ester (CE) in isolated hepatocytes from fasted rats. Hepatocytes were incubated in Krebs-Henseleit bicarbonate buffer containing bovine plasma albumin for 90 min with 0, 1, 2, or 3 mM P at constant specific radioactivity. Lipids were extracted and isolated by thin layer chromatography. Chemical TG was also determined. [3H]-P was esterified primarily to TG (70-90% of the total radioactivity in lipids) and increased in proportion to the P conc. The amount of [3H]-P incorporated into PL and CE was similar at all added P conc's. After this period of lipid deposition, the cells were washed to remove P, and mobilization of esterified P was assessed by incubation for an additional 90 min in P-free media. The rate of mobilization of TG increased in proportion to the intracellular TG conc. The amount of [3H]-P mobilized from PL and CE was much lower than that released from TG and was similar for all levels of P present during the period of lipid deposition. This system provides a useful model for investigating mechanisms of deposition and mobilization of TG in intact liver cells. Under the conditions employed, mobilization of TG fatty acids from storage pools was a non-saturable process