Hideo Hatta

Negligible direct lactate oxidation in subsarcolemmal and intermyofibrillar mitochondria obtained from red and white rat skeletal muscle

We examined the controversial notion of whether lactate is directly oxidized by subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria obtained from red and white rat skeletal muscle. Respiratory control ratios were normal in SS and IMF mitochondria. At all concentrations (0.18–10 mm), and in all mitochondria, pyruvate oxidation greatly exceeded lactate oxidation, by 31‐ to 186‐fold. Pyruvate and lactate oxidation were inhibited by α‐cyano‐4‐hydroxycinnamate, while lactate oxidation was inhibited by oxamate. Excess pyruvate (10 mm) inhibited the oxidation of palmitate (1.8 mm) as well as lactate (1.8 mm). In contrast, excess lactate (10 mm) failed to inhibit the oxidation of either palmitate (1.8 mm) or pyruvate (1.8 mm). The cell‐permeant adenosine analogue, AICAR, increased pyruvate oxidation; in contrast, lactate oxidation was not altered. The monocarboxylate transporters MCT1 and 4 were present on SS mitochondria, but not on IMF mitochondria, whereas, MCT2, a high‐affinity pyruvate transporter, was present in both SS and IMF mitochondria. The lactate dehydrogenase (LDH) activity associated with SS and IMF mitochondria was 200‐ to 240‐fold lower than in whole muscle. Addition of LDH increased the rate of lactate oxidation, but not pyruvate oxidation, in a dose‐dependent manner, such that lactate oxidation approached the rates of pyruvate oxidation. Collectively, these studies indicate that direct mitochondrial oxidation of lactate (i.e. an intracellular lactate shuttle) does not occur within the matrix in either IMF or SS mitochondria obtained from red or white rat skeletal muscle, because of the very limited quantity of LDH within mitochondria.

Exercise rapidly increases expression of the monocarboxylate transporters MCT1 and MCT4 in rat muscle

We examined the effect of a single exercise session on the protein and mRNA expression of the monocarboxylate transporters MCT1 and MCT4 in rat soleus (SOL), and red (RG) and white gastrocnemius (WG) muscles. Muscle samples were obtained at rest before 2 h of treadmill exercise (21 m min−1, 15% grade) and immediately after exercise, as well as 5, 10 and 24 h after exercise. During the 2 h exercise bout, MCT1 proteins in RG (+60%) and WG (+56%) were increased (P < 0.05). MCT1 protein was further increased thereafter, with peak increments occurring 10 h after exercise in RG (+157%), WG (+193%) and SOL (+179%) (P < 0.05). Twenty‐four hours after exercise, MCT1 protein was still up‐regulated in WG (+100%) and SOL (+55%) (P < 0.05), but not in RG. MCT1 mRNA was up‐regulated during exercise in RG (+53%) and WG (+98%) and remained elevated until 24 h post‐exercise in RG (P < 0.05), but in WG, MCT1 mRNA decreased transiently to pre‐exercise levels at 5 and 10 h after exercise, before increasing again at 24 h (+150%) (P < 0.05). MCT4 protein and mRNA were not increased in WG muscle during and after exercise (P > 0.05). In contrast, during exercise, in RG (+41%) and SOL (+98%) MCT4 protein was increased (P < 0.05). Peak increases in MCT4 protein were observed 10 h after exercise in RG (+131%) and SOL (+323%) (P < 0.05). MCT4 protein was still up‐regulated 24 h after exercise (RG: +106%; SOL +225%) (P < 0.05). MCT4 mRNA in RG was not increased until 10 (+132%) and 24 h after exercise (+55%) (P < 0.05). These studies have shown that MCT1 and 4 proteins are transiently up‐regulated by a single bout of exercise, involving post‐transcriptional and transcriptional mechanisms. Thus, MCT1 and MCT4 belong to a class of selected metabolic genes that are very rapidly up‐regulated with an exercise stimulus.

PGC-1α increases skeletal muscle lactate uptake by increasing the expression of MCT1 but not MCT2 or MCT4

We examined the relationship between PGC-1alpha protein; the monocarboxylate transporters MCT1, 2, and 4; and CD147 1) among six metabolically heterogeneous rat muscles, 2) in chronically stimulated red (RTA) and white tibialis (WTA) muscles (7 days), and 3) in RTA and WTA muscles transfected with PGC-1alpha-pcDNA plasmid in vivo. Among rat hindlimb muscles, there was a strong positive association between PGC-1alpha and MCT1 and CD147, and between MCT1 and CD147. A negative association was found between PGC-1alpha and MCT4, and CD147 and MCT4, while there was no relationship between PGC-1alpha or CD147 and MCT2. Transfecting PGC-1alpha-pcDNA plasmid into muscle increased PGC-1alpha protein (RTA +23%; WTA +25%) and induced the expression of MCT1 (RTA +16%; WTA +28%), but not MCT2 and MCT4. As a result of the PGC-1alpha-induced upregulation of MCT1 and its chaperone CD147 (+29%), there was a concomitant increase in the rate of lactate uptake (+20%). In chronically stimulated muscles, the following proteins were upregulated, PGC-1alpha in RTA (+26%) and WTA (+86%), MCT1 in RTA (+61%) and WTA (+180%), and CD147 in WTA (+106%). In contrast, MCT4 protein expression was not altered in either RTA or WTA muscles, while MCT2 protein expression was reduced in both RTA (-14%) and WTA (-10%). In these studies, whether comparing oxidative capacities among muscles or increasing their oxidative capacities by PGC-1alpha transfection and chronic muscle stimulation, there was a strong relationship between the expression of PGC-1alpha and MCT1, and PGC-1alpha and CD147 proteins. Thus, MCT1 and CD147 belong to the family of metabolic genes whose expression is regulated by PGC-1alpha in skeletal muscle.

Testosterone increases lactate transport, monocarboxylate transporter (MCT) 1 and MCT4 in rat skeletal muscle

We have examined the effects of administration of testosterone for 7 days on monocarboxylate transporter (MCT) 1 and MCT4 mRNAs and proteins in seven metabolically heterogeneous rat hindlimb muscles and in the heart. In addition, we also examined the effects of testosterone treatment on plasmalemmal MCT1 and MCT4, and lactate transport into giant sarcolemmal vesicles prepared from red and white hindlimb muscles and the heart. Testosterone did not alter MCT1 or MCT4 mRNA, except in the plantaris muscle. Testosterone increased MCT1 (20%–77%, P < 0.05) and MCT4 protein (29%–110%, P< 0.05) in five out of seven muscles examined. In contrast, in the heart MCT1 protein was not increased (P> 0.05), and MCT 4 mRNA and protein were not detected. There was no correlation between the testosterone‐induced increments in MCT1 and MCT4 proteins. Muscle fibre composition was not associated with testosterone‐induced increments in MCT1 protein. In contrast, there was a strong positive relationship between the testosterone‐induced increments in MCT4 protein and the fast‐twitch fibre composition of rat muscles. Lactate transport into giant sarcolemmal vesicles was increased in red (23%, P< 0.05) and white muscles (21%, P< 0.05), and in the heart (58%, P< 0.05) of testosterone‐treated animals (P< 0.05). However, plasmalemmal MCT1 protein (red, +40%, P< 0.05; white, +39%, P< 0.05) and plasmalemmal MCT4 protein (red, +25%, P< 0.05; white, +48%, P< 0.05) were increased only in skeletal muscle. In the heart, plasmalemmal MCT1 protein was reduced (−20%, P< 0.05). In conclusion, these studies have shown that testosterone induces an increase in both MCT1 and MCT4 proteins and their plasmalemmal content in skeletal muscle. However, the testosterone‐induced effect was tissue‐specific, as MCT1 protein expression was not altered in the heart. In the heart, the testosterone‐induced increase in lactate transport cannot be explained by changes in plasmalemmal MCT1 content, but in skeletal muscle the increase in the rate of lactate transport was associated with increases in plasmalemmal MCT1 and MCT4.

Daily physical activity levels in preadolescent boys related to\(\dot V_{O_{2max} } \) and lactate threshold

SummaryThe purpose of this study was to investigate the physical activity levels in eleven 9–10 year old boys with reference to aerobic power or lactate threshold (LT). Daily physical activity levels were evaluated from a HR monitoring system for 12 h on three different days.

Tissue stiffness induced by prolonged immobilization of the rat knee joint and relevance of AGEs (pentosidine)

\dot V_{O_{2max} }

Postexercise whole body heat stress additively enhances endurance training-induced mitochondrial adaptations in mouse skeletal muscle

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