Downregulation in muscle Na+-K+-ATPase following a 21-day expedition to 6,194 m

Authors:
  • VWV. L. Wyckelsma
    V. L. Wyckelsma
  • BPB. D. Perry
    B. D. Perry
  • JBJ. Bangsbo
    J. Bangsbo
  • MMM. J. McKenna
    M. J. McKenna
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Abstract
To investigate the hypothesis that acclimatization to altitude would result in a downregulation in muscle Na+-K+-ATPase pump concentration, tissue samples were obtained from the vastus lateralis muscle of six volunteers (5 males and 1 female), ranging in age from 24 to 35 yr, both before and within 3 days after a 21-day expedition to the summit of Mount Denali, Alaska (6,194 m). Na+-K+-ATPase, measured by the [3H]ouabain-binding technique, decreased by 13.8% [348 ± 12 vs. 300 ± 7.6 (SE) pmol/g wet wt; P< 0.05]. No changes were found in the maximal activities (mol ⋅ kg protein− 1 ⋅ h− 1) of the mitochondrial enzymes, succinic dehydrogenase (3.63 ± 0.20 vs. 3.25 ± 0.23), citrate synthase (4.76 ± 0.44 vs. 4.94 ± 0.44), and malate dehydrogenase (12.6 ± 1.8 vs. 12.7 ± 1.2). Similarly, the expedition had no effect on any of the histochemical properties examined, namely fiber-type distribution (types I, IIA, IIB, IC, IIC, IIAB), area, capillarization, and succinic dehydrogenase activity. Peak aerobic power (52.3 ± 2.1 vs. 50.6 ± 1.9 ml ⋅ kg− 1 ⋅ min− 1) and body mass (76.9 ± 3.7 vs. 75.5 ± 2.9 kg) were also unaffected. We concluded that acclimatization to altitude results in a downregulation in muscle Na+-K+-ATPase pump concentration, which occurs without changes in oxidative potential and other fiber-type histochemical properties.

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