Lactate transport in rat sarcolemmal vesicles after a single bout of submaximal exercise

We investigated the effects of a single bout of non-exhaustive exercise (25 m x min(-1), 10% grade, for 30 min) on the initial rates of lactate uptake in rat skeletal muscle sarcolemmal vesicles and the monocarboxylate transp orter 1 (MCT1) content in isolated hindlimb muscles in relation to the exer cise-induced oxidative stress. The exercise led to a decrease in red gastro cnemius and red vastus lateralis muscle glycogen content by 74% and 83%, re spectively, and an increase in blood lactate concentration from 1.67 +/- 0. 15 to 3.44 +/- 0.47 mM (p < 0.05). Initial rates of lactate uptake were mea sured in zero-trans conditions, at pH 7.4, for 1, 10, 30 and 100 mM externa l lactate concentrations. Lactate transport capacity was significantly decr eased at 1 mM in the exercised group (p<0.05), while a non-significant tren d towards an increase was observed at 10, 30 and 100 mM. We failed to obtai n any change in soleus, red tibialis anterior and white gastrocnemius muscl e MCT1 content (p>0.05), and no evidence of exercise-induced oxidative stre ss in terms of muscle malondialdehyde content and glutathione peroxidase an d superoxide dismutase activities was observed after the 30 min exercise bo ut. These results indicate that a single bout of submaximal exercise, which did not induce an increase in muscle MCT1 content and apparent oxidative s tress, decreased lactate transport capacity at low physiological concentrat ion. Although the changes are small and independent of a MCT1-facilitated l actate transport regulation, we suggest that another MCT isoform with diffe rent kinetic properties from MCT1 could be present in the sarcolemma and re sponsible for lactate exchange alterations.