CHRONIC ELECTRICAL-STIMULATION INCREASES MCT1 AND LACTATE UPTAKE IN RED AND WHITE SKELETAL-MUSCLE

We examined whether chronic stimulation of red and white rat muscles i ncreased the concentrations of the monocarboxylate transporter MCT1. R ed and white tibialis anterior (RTA and WTA, respectively) and extenso r digitorum longus (EDL) muscles were chronically stimulated via the p eroneal nerve for 7 days. Stimulated and contralateral control muscles were examined for MCT1 content, L-lactate uptake, lactate dehydrogena se (LDH) isoforms, and muscle fiber composition. MCT1 was 1.5 times gr eater in stimulated RTA, 3 times greater in stimulated WTA, and 1.9 ti mes greater in stimulated EDL compared with respective control muscles (P < 0.05). L-Lactate uptake increased in all stimulated muscles (P < 0.05), and this was highly correlated with the increase in MCT1 (r = 0.96). The heart-type LDH (H-LDH) subunits also increased in all stimu lated muscles (P < 0.05). The H-LDH subunits correlated highly with MC T1 in the muscles (r = 0.83). There was no change in muscle-type LDH s ubunits (P > 0.05). There were negligible alterations in muscle fiber composition in the stimulated muscles, suggesting that the increase in MCT1 was independent of changes in muscle fiber composition. These st udies are the first to demonstrate that chronic muscle contraction inc reases MCT1 concentrations in both red and white skeletal muscles.