Triacylglycerol synthesis in the different skeletal muscle fiber sections of the rat

Triacylglycerol (TG) synthesis rates of low-oxidative fast-twitch white and high-oxidative fast- and slow-twitch red skeletal muscle fiber sections of adult rats were measured by the incorporation of perfusate-derived palmitate into the neutral lipid fraction by use of a perfused hindquarter preparation under high-flow conditions. The perfusion medium consisted of 95% O-2-5% CO2 Krebs-Henseleit buffer, pH 1.4, containing 5 g/100 ml bovine serum albumin, 100 mu U/ml insulin, 5 mmol/l glucose, amino acids, and added fatty acids (FA), including 0.1 mu Ci/ml [H-3]palmitate. FA incorporation was linear with time. TG synthesis rates correlated (r greater than or equal to 0.90) with the oxidative capacity of each of the different fiber type sections and increased in proportion to the perfusate FA concentration (0.25, 0.5, 1.0, 1.5, and 2.0 mmol/l). TG synthesis rates among different muscle fiber sections were related (r greater than or equal to 0.90) to perfusate flow during high-flow conditions; however, this was not causal, because TG synthesis rates within each muscle fiber section were independent of flow rate when experimentally varied over an approximately threefold range. Thus the relatively high TG synthesis rates observed in the high-oxidative muscle sections are not uniquely related to their high-flow capacities but are inherent to the TG synthesis process, probably events associated with FA uptake and/or capacity of the TG synthesis pathway.