title: Downregulation of Na+-K+-ATPase pumps in skeletal muscle with training in normobaric hypoxia.
abstract: To investigate the effects of training in normoxia vs. training in normobaric hypoxia (fraction of inspired O2 = 20.9 vs. 13.5%, respectively) on the regulation of Na+-K+-ATPase pump concentration in skeletal muscle (vastus lateralis), 9 untrained men, ranging in age from 19 to 25 yr, underwent 8 wk of cycle training. The training consisted of both prolonged and intermittent single leg exercise for both normoxia (N) and hypoxia (H) during a single session (a similar work output for each leg) and was performed 3 times/wk. Na+-K+-ATPase concentration was 326 +/- 17 (SE) pmol/g wet wt before training (Control), increased by 14% with N (371 +/- 18 pmol/g wet wt; P < 0.05), and decreased by 14% with H (282 +/- 20 pmol/g wet wt; P < 0.05). The maximal activity of citrate synthase, selected as a measure of mitochondrial potential, showed greater increases (P < 0.05) with H (1.22 +/- 0.10 mmol x h-1 x g wet wt-1; 70%; P < 0.05) than with N (0.99 +/- 0.10 mmol x h-1 x g wet wt-1; 51%; P < 0.05) compared with pretraining (0.658 +/- 0.09 mmol x h-1 x g wet wt-1). These results demonstrate that normobaric hypoxia induced during exercise training represents a potent stimulus for the upregulation in mitochondrial potential while at the same time promoting a downregulation in Na+-K+-ATPase pump expression. In contrast, normoxic training stimulates increases in both mitochondrial potential and Na+-K+-ATPase concentration.
authors.affiliation: Department of Kinesiology, University of Waterloo, Ontario N2L 3G1.
authors.forename: H
authors.initials: H
authors.lastname: Green
authors.forename: J
authors.initials: J
authors.lastname: MacDougall
authors.forename: M
authors.initials: M
authors.lastname: Tarnopolsky
authors.forename: N L
authors.initials: NL
authors.lastname: Melissa
mesh_terms: D000328:Adult; D002950:Citrate (si)-Synthase / Q000378:metabolism; D015536:Down-Regulation / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000201:enzymology* / Q000503:physiopathology*; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology* / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis*
chemical_list: D002950:Citrate (si)-Synthase; D000254:Sodium-Potassium-Exchanging ATPase