title: Effects of progressive exercise and hypoxia on human muscle sarcoplasmic reticulum function.
abstract: This study examined the effects of progressive exercise to fatigue in normoxia (N) on muscle sarcoplasmic reticulum (SR) Ca(2+) cycling and whether alterations in SR Ca(2+) cycling are related to the blunted peak mechanical power output (PO(peak)) and peak oxygen consumption (Vo(2 peak)) observed during progressive exercise in hypoxia (H). Nine untrained men (20.7 +/- 0.42 yr) performed progressive cycle exercise to fatigue on two occasions, namely during N (inspired oxygen fraction = 0.21) and during H (inspired oxygen fraction = 0.14). Tissue extracted from the vastus lateralis before exercise and at power output corresponding to 50 and 70% of Vo(2 peak) (as determined during N) and at fatigue was used to investigate changes in homogenate SR Ca(2+)-cycling properties. Exercise in H compared with N resulted in a 19 and 21% lower (P < 0.05) PO(peak) and Vo(2 peak), respectively. During progressive exercise in N, Ca(2+)-ATPase kinetics, as determined by maximal activity, the Hill coefficient, and the Ca(2+) concentration at one-half maximal activity were not altered. However, reductions with exercise in N were noted in Ca(2+) uptake (before exercise = 357 +/- 29 micromol x min(-1) x g protein(-1); at fatigue = 306 +/- 26 micromol x min(-1) x g protein(-1); P < 0.05) when measured at free Ca(2+) concentration of 2 microM and in phase 2 Ca(2+) release (before exercise = 716 +/- 33 micromol x min(-1) x g protein(-1); at fatigue = 500 +/- 53 micromol x min(-1) x g protein(-1); P < 0.05) when measured in vitro in whole muscle homogenates. No differences were noted between N and H conditions at comparable power output or at fatigue. It is concluded that, although structural changes in SR Ca(2+)-cycling proteins may explain fatigue during progressive exercise in N, they cannot explain the lower PO(peak) and Vo(2 peak) observed during H.
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: S D
authors.initials: SD
authors.lastname: Sandiford
authors.forename: J G
authors.initials: JG
authors.lastname: Perco
authors.forename: J
authors.initials: J
authors.lastname: Ouyang
mesh_terms: D000328:Adult; D000332:Aerobiosis; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D018592:Cross-Over Studies; D015444:Exercise / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D007700:Kinetics; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology*; D011659:Pulmonary Gas Exchange; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D000252:Calcium-Transporting ATPases; D002118:Calcium