title: Human muscle sarcoplasmic reticulum function during submaximal exercise in normoxia and hypoxia.
abstract: 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 approximately 25% at 30 min of exercise compared with rest (168 +/- 10 vs. 126 +/- 8 micromol.g protein(-1) x min(-1)), with no further reductions observed at 90 min (129 +/- 6 micromol x g protein(-1) x 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 approximately 20% (370 +/- 22 vs. 298 +/- 25 micromol x g protein(-1) x min(-1)). Ca(2+) release, induced by 4-chloro-m-cresol and assessed into fast and slow phases, was decreased (P < 0.05) by approximately 16 and approximately 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.
authors.affiliation: Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
authors.forename: T A
authors.initials: TA
authors.lastname: Duhamel
authors.forename: H J
authors.initials: HJ
authors.lastname: Green
authors.forename: J G
authors.initials: JG
authors.lastname: Perco
authors.forename: S D
authors.initials: SD
authors.lastname: Sandiford
authors.forename: J
authors.initials: J
authors.lastname: Ouyang
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D018592:Cross-Over Studies; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D007700:Kinetics; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology / Q000502:physiology*; D011659:Pulmonary Gas Exchange; D012519:Sarcoplasmic Reticulum / Q000201:enzymology / Q000502:physiology*
chemical_list: D000252:Calcium-Transporting ATPases; D002118:Calcium