Prolonged exercise to fatigue in humans impairs skeletal muscle Na+-K+-ATPase activity, sarcoplasmic reticulum Ca2+ release, and Ca2+ uptake

• Published in: Journal of applied physiology (1985) 2004-10, Vol.97 (4), p.1414-1423
• Main Authors: Leppik, James A, Aughey, Robert J, Medved, Ivan, Fairweather, Ian, Carey, Michael F, McKenna, Michael J
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological - physiology; Adult; Biological and medical sciences; Calcium - metabolism; Enzyme Activation; Exercise - physiology; Exercise Test; Female; Fundamental and applied biological sciences. Psychology; Humans; Male; Muscle Contraction - physiology; Muscle Fatigue - physiology; Muscle, Skeletal - physiology; Physical Endurance - physiology; Sarcoplasmic Reticulum - physiology; Sodium-Potassium-Exchanging ATPase - metabolism; Thigh - physiology
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00964.2003

1 Muscle, Ions, and Exercise Group, School of Human Movement, Recreation and Performance, and 2 School of Life Sciences and Technology, Centre for Aging, Rehabilitation, Exercise, and Sport, Victoria University of Technology, Melbourne 8001, Australia Submitted 8 September 2003 ; accepted in final form 14 May 2004 Prolonged exhaustive submaximal exercise in humans induces marked metabolic changes, but little is known about effects on muscle Na + -K + -ATPase activity and sarcoplasmic reticulum Ca 2+ regulation. We therefore investigated whether these processes were impaired during cycling exercise at 74.3 ± 1.2% maximal O 2 uptake (mean ± SE) continued until fatigue in eight healthy subjects (maximal O 2 uptake of 3.93 ± 0.69 l/min). A vastus lateralis muscle biopsy was taken at rest, at 10 and 45 min of exercise, and at fatigue. Muscle was analyzed for in vitro Na + -K + -ATPase activity [maximal K + -stimulated 3- O -methylfluorescein phosphatase (3- O -MFPase) activity], Na + -K + -ATPase content ([ 3 H]ouabain binding sites), sarcoplasmic reticulum Ca 2+ release rate induced by 4 chloro- m -cresol, and Ca 2+ uptake rate. Cycling time to fatigue was 72.18 ± 6.46 min. Muscle 3- O -MFPase activity (nmol·min –1 ·g protein –1 ) fell from rest by 6.6 ± 2.1% at 10 min ( P < 0.05), by 10.7 ± 2.3% at 45 min ( P < 0.01), and by 12.6 ± 1.6% at fatigue ( P < 0.01), whereas 3 [H]ouabain binding site content was unchanged. Ca 2+ release (mmol·min –1 ·g protein –1 ) declined from rest by 10.0 ± 3.8% at 45 min ( P < 0.05) and by 17.9 ± 4.1% at fatigue ( P < 0.01), whereas Ca 2+ uptake rate fell from rest by 23.8 ± 12.2% at fatigue ( P = 0.05). However, the decline in muscle 3- O -MFPase activity, Ca 2+ uptake, and Ca 2+ release were variable and not significantly correlated with time to fatigue. Thus prolonged exhaustive exercise impaired each of the maximal in vitro Na + -K + -ATPase activity, Ca 2+ release, and Ca 2+ uptake rates. This suggests that acutely downregulated muscle Na + , K + , and Ca 2+ transport processes may be important factors in fatigue during prolonged exercise in humans. calcium ion ATPase; sodium-potassium pump; potassium Address for reprint requests and other correspondence: M. J. McKenna, School of Human Movement, Recreation and Performance (FO22), Victoria Univ. of Technology, PO Box 14428, MCMC, Melbourne, Victoria 8001, Australia (E-mail: michael.mckenna{at}vu.edu.au ).