Cardiac and skeletal muscle mitochondria have a monocarboxylate transporter MCT1

To evaluate the potential role of monocarboxylate transporter-1 (MCT1) in t issue lactate oxidation, isolated rat subsarcolemmal and interfibrillar car diac and skeletal muscle mitochondria were probed with an antibody to MCT1. Western blots indicated presence of MCT1 in sarcolemmal membranes and in s ubsarcolemmal and interfibrillar mitochondria. Minimal cross-contamination of mitochondria by cell membrane fragments was verified by probing for the sarcolemmal protein GLUT-1. In agreement, immunolabeling and electron micro scopy showed mitochondrial MCT1 in situ. Along with lactic dehydrogenase, t he presence of MCT1 in striated muscle mitochondria permits mitochondrial l actate oxidation and facilitates function of the "intracellular lactate shu ttle."