TRAINING-INDUCED INCREASE IN FABPPM IS ASSOCIATED WITH ELEVATIONS IN PALMITATE UPTAKE AND OXIDATION BY CONTRACTING MUSCLE 456

Abstract

Endurance training has been shown to be associated with an increased contribution of lipids to oxidative metabolism in exercising muscles. To evaluate a mechanism for this change, we measured the uptake and oxidation of palmitate in isolated rat hindquarters as well as the content of fatty acid-binding proteins in the plasma membranes (FABPPM) of red and white muscles from 16 trained (T) and 18 untrained (UT) rats. Hindquarters were perfused with 6 mM glucose, 1800 μM albumin-bound palmitate and albumin-bound [1-14C]palmitate at rest and during electrical stimulation (100 ms trains at 100 Hz, 20 trains/min) for 25 min (ES). FABPPM content was 1.5 to 3-fold higher in red than in white muscles and was increased by 56% after endurance training in red muscles. A positive correlation (r=0.78, p<0.05) was found to exist between SDH activity and FABPPM content in red muscles. Palmitate uptake increased by 60-65% from rest to ES in both T and UT and was 30-35% higher in T than UT both at rest (29.4±2.7 vs 39.6±2.5 nmol·min-1·g-1 for UT and T, respectively) and during ES (48.7±4.2 vs 63.5±5.1 nmol·min-1·g-1 for UT and T, respectively). Resting palmitate oxidation was not affected by training and averaged 1.7±0.3 nmol·min-1·g-1. During ES, palmitate oxidation was higher in T than UT (12.1±1.7 vs 7.3±0.5 nmol·min-1·g-1, respectively). It is concluded that endurance training increases plasma FFA uptake in resting and contracting perfused muscle and plasma FFA oxidation in contracting perfused muscle. Furthermore, endurance training increases FABPPM content in red muscles, suggesting that an increased number of transporters may be available in the trained muscle. The data are consistent with the notion that the putative plasma membrane carrier of FFA may be implicated in the regulation of plasma FFA metabolism in skeletal muscle.