Human muscle sarcoplasmic reticulum function during submaximal exercise in normoxia and hypoxia

• Published in: Journal of applied physiology (1985) 2004-07, Vol.97 (1), p.180-187
• Main Authors: Duhamel, T. A, Green, H. J, Perco, J. G, Sandiford, S. D, Ouyang, J
• Format: Article
• Language: English
• Subjects: Adult; Bicycling; Bicycling - physiology; Biological and medical sciences; Calcium; Calcium - metabolism; Calcium Signaling - physiology; Calcium-Transporting ATPases - metabolism; Cross-Over Studies; Exercise; Exercise - physiology; Exercise Test; Fundamental and applied biological sciences. Psychology; Humans; Hypoxia - physiopathology; Kinetics; Male; Medical research; Muscle, Skeletal - enzymology; Muscle, Skeletal - physiology; Muscular system; Pulmonary Gas Exchange; Sarcoplasmic Reticulum - enzymology; Sarcoplasmic Reticulum - physiology
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00954.2003

Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 Submitted 4 September 2003 ; accepted in final form 14 March 2004 In this study, the response of the sarcoplasmic reticulum (SR) to prolonged exercise, performed in normoxia (inspired O 2 fraction = 0.21) and hypoxia (inspired O 2 fraction = 0.14) was studied in homogenates prepared from the vastus lateralis muscle in 10 untrained men (peak O 2 consumption = 3.09 ± 0.25 l/min). In normoxia, performed at 48 ± 2.2% peak O 2 consumption, maximal Ca 2+ -dependent ATPase activity was reduced by 25% at 30 min of exercise compared with rest (168 ± 10 vs. 126 ± 8 µmol·g protein –1 ·min –1 ), with no further reductions observed at 90 min (129 ± 6 µmol·g protein –1 ·min –1 ). No changes were observed in the Hill coefficient or in the Ca 2+ concentration at half-maximal activity. The reduction in maximal Ca 2+ -dependent ATPase activity at 30 min of exercise was accompanied by oxalate-dependent reductions ( P < 0.05) in Ca 2+ uptake by 20% (370 ± 22 vs. 298 ± 25 µmol·g protein –1 ·min –1 ). Ca 2+ release, induced by 4-chloro- m -cresol and assessed into fast and slow phases, was decreased ( P < 0.05) by 16 and 32%, respectively, by 90 min of exercise. No differences were found between normoxia and hypoxia for any of the SR properties examined. It is concluded that the disturbances induced in SR Ca 2+ cycling with prolonged moderate-intensity exercise in human muscle during normoxia are not modified when the exercise is performed in hypoxia. calcium, cycling; vastus lateralis; prolonged activity Address for reprint requests and other correspondence: H. J. Green, Dept. of Kinesiology, Univ. of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (E-mail: green{at}healthy.uwaterloo.ca ).