ROLE OF THE LACTATE TRANSPORTER (MCT1) IN SKELETAL-MUSCLES

We used an antibody, constructed against the monocarboxylate transport er 1 (MCT1) protein (L. Carpenter, R. C. Poole, and A. P. Halestrap. B iochim. Biophys. Acta 1279: 157-165, 1996), to study the expression an d role of MCT1 in rat skeletal muscles. MCT1 was higher in red than in white muscles (P < 0.05) and was highly correlated with the oxidative fiber content (%slow-twitch oxidative + %fast-twitch oxidative glycol ytic) of skeletal muscles (r = 0.91). MCT1 was highly related to lacta te uptake in skeletal muscles (r = 0.90). Total lactate dehydrogenase (LDH) activity, an index of glycolysis, was negatively correlated with MCT1 in rat muscles (r = -0.80). MCT1 was also strongly correlated wi th the heart-type forms of LDH (LDH-1 vs. MCT1, r = 0.83; LDH-2 vs. MC T1, r = 0.89). There was no relationship between MCT1 and the muscle f orm of LDH (LDH-5; P > 0.05). MCT1 was highly correlated with citrate synthase activity, a marker of the oxidative capacity of muscle (r = 0 .82). Therefore, MCT1 may have kinetics that favor the uptake of L-lac tate into the muscle cell for oxidative metabolism, and MCT1 may be co ordinately expressed with the heart forms of LDH and enzymes of oxidat ive metabolism.