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1 Department of Kinesiology, University of Waterloo, Waterloo N2L3G1; 2 Ottawa Heart Institute, University of Ottawa, Ottawa, Ontario K1Y4E9; and 3 Division of Sports Medicine, University of British Columbia, British Columbia, Canada V6T1Z3
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 · h1)
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 · kg1 · min1)
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.
enzyme, cation pump; fiber characteristics
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