Expression of MCT1 and MCT4 in a patient with mitochondrial myopathy

Mitochondrial myopathies (MM) are characterized by alterations in oxidative phosphorylation. The resultant increase in glycolytic flux produces a vari able lactic acidosis. Intracellular acidification can induce both metabolic and, in the case of skeletal muscle, contractile dysfunction. Skeletal mus cle lactate transporters have recently been identified which include both m onocarboxylate transporter 1 (MCT1) and 4 (MCT4), Lactate import into oxida tive skeletal muscle appears to be catalyzed by MCT1, whereas its extrusion from glycolytic fibers may be mediated by MCT4. We describe the expression of these isoforms in a patient with MM as compared to controls (n = 5). MC T4 content was 86% (>3 SD) higher in the patient with MM, whereas MCT1 cont ent was less markedly elevated (47%), as compared to controls. These findin gs support previous work suggesting that the major role of MCT4 is to defen d intracellular pH by extruding lactate and H+ to the interstitium. The rol e of MCT1 in MM is less clear. (C) 2001 John Wiley & Sons, Inc.