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."