Lactate/H+ transport kinetics in rat skeletal muscle related to fibre type and changes in transport capacity.
Lactate/H+ transport kinetics were determined by means of the pH-sensitive probe BCECF in sarcolemmal giant vesicles, obtained from rat skeletal muscle, and related to variations in lactate/H+ transport capacity. Vesicle preparations were made from red and white muscles, mixed muscles, denervated muscles, muscles of old rats and rats that had been subjected to high-intensity training, endurance training, repeated exposure to hypoxia, and hypothyroid or hyperthyroid treatments. The lactate/H+ transport capacity of red muscles was greater than that of white muscles, and this difference was associated with a higher maximal transport rate (V max) in red muscles, whereas the K m was similar in the two muscle types. High-intensity training and hyperthyroidism increased the lactate/H+ transport capacity by enhancing V max without affecting K m. Similarly, a reduced transport capacity with old age and hypothyroidism was due to a decrease in V max. The denervation-induced decline in lactate/H+ transport capacity resulted from both an increased K m and a reduced V max. The present data show that muscle type differences and most changes in the lactate/H+ transport capacity are mediated by modifications in V max, which is expected to represent the number of membrane transporter molecules. K m is unaffected by most treatments and appears to be independent of fibre type.
University of Copenhagen, Universitetsparken 13, 2100 Denmark.
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Juel
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Pilegaard
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D019344:Lactic Acid / Q000378:metabolism*; D008297:Male; D027501:Monocarboxylic Acid Transporters / Q000378:metabolism*; D009121:Muscle Denervation; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology* / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D011522:Protons; D051381:Rats; D017208:Rats, Wistar; D013961:Thyroid Gland / Q000378:metabolism
D027501:Monocarboxylic Acid Transporters; D020033:Protein Isoforms; D011522:Protons; D019344:Lactic Acid