Inactivation of human muscle Na+-K+-ATPase in vitro during prolonged exercise is increased with hypoxia

• Published in: Journal of applied physiology (1985) 2004-05, Vol.96 (5), p.1767-1775
• Main Authors: Sandiford, S. D, Green, H. J, Duhamel, T. A, Perco, J. G, Schertzer, J. D, Ouyang, J
• Format: Article
• Language: English
• Subjects: Adult; Bicycling; Biological and medical sciences; Electric Stimulation; Electromyography; Enzyme Activation; Exercise; Fatigue; Female; Fundamental and applied biological sciences. Psychology; Humans; Hypoxia - enzymology; Isometric Contraction; Male; Muscle Contraction; Muscle Fatigue; Muscle, Skeletal - enzymology; Muscle, Skeletal - physiopathology; Muscular system; Neuromuscular Junction - physiopathology; Oxygen Consumption; Physical Endurance; Respiratory system; Single-Blind Method; Sodium-Potassium-Exchanging ATPase - metabolism
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.01273.2003

Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 Submitted 1 December 2003 ; accepted in final form 8 January 2004 This study investigated the effects of prolonged exercise performed in normoxia (N) and hypoxia (H) on neuromuscular fatigue, membrane excitability, and Na + -K + -ATPase activity in working muscle. Ten untrained volunteers [peak oxygen consumption (V O 2 peak ) = 42.1 ± 2.8 (SE) ml·kg -1 ·min -1 ] performed 90 min of cycling during N (inspired oxygen fraction = 0.21) and during H (inspired oxygen fraction = 0.14) at 50% of normoxic V O 2 peak . During N, 3- O -methylfluorescein phosphatase activity (nmol·mg protein -1 ·h -1 ) in vastus lateralis, used as a measure of Na + -K + -ATPase activity, decreased ( P < 0.05) by 21% at 30 min of exercise compared with rest (101 ± 53 vs. 79.6 ± 4.3) with no further reductions observed at 90 min (72.8 ± 8.0). During H, similar reductions ( P < 0.05) were observed during the first 30 min (90.8 ± 5.3 vs. 79.0 ± 6.3) followed by further reductions ( P < 0.05) at 90 min (50.5 ± 3.9). Exercise in N resulted in reductions ( P < 0.05) in both quadriceps maximal voluntary contractile force (MVC; 633 ± 50 vs. 477 ± 67 N) and force at low frequencies of stimulation, namely 10 Hz (142 ± 16 vs. 86.7 ± 10 N) and 20 Hz (283 ± 32 vs. 236 ± 31 N). No changes were observed in the amplitude, duration, and area of the muscle compound action potential (M wave). Exercise in H was without additional effect in altering MVC, low-frequency force, and M-wave properties. It is concluded that, although exercise in H resulted in a greater inactivation of Na + -K + -ATPase activity compared with N, neuromuscular fatigue and membrane excitability are not differentially altered. membrane excitability; sodium-potassium-adenosinetriphosphatase activity; fatigue Address for reprint requests and other correspondence: H. J. Green, Dept. of Kinesiology, University of Waterloo, Waterloo, ON, Canada N2L 3G1 (E-mail: green{at}healthy.uwaterloo.ca ).