title: Adaptations in human muscle sarcoplasmic reticulum to prolonged submaximal training.
abstract: In this study, we employed single-leg submaximal cycle training, conducted over a 10-wk period, to investigate adaptations in sarcoplasmic reticulum (SR) Ca(2+)-regulatory proteins and processes of the vastus lateralis. During the final weeks, the untrained volunteers (age 21.4 +/- 0.3 yr; means +/- SE, n = 10) were exercising 5 times/wk and for 60 min/session. Analyses were performed on tissue extracted by needle biopsy approximately 4 days after the last training session. Compared with the control leg, the trained leg displayed a 19% reduction (P < 0.05) in homogenate maximal Ca(2+)-ATPase activity (192 +/- 11 vs. 156 +/- 18 micromol. g protein(-1). min(-1)), a 4.3% increase (P < 0.05) in pCa(50), defined as the Ca(2+) concentration at half-maximal activity (6.01 +/- 0.05 vs. 6.26 +/- 0.07), and no change in the Hill coefficient (1.75 +/- 0.15 vs. 1.76 +/- 0.21). Western blot analysis using monoclonal antibodies (7E6 and A52) revealed a 13% lower (P < 0.05) sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) 1 in trained vs. control in the absence of differences in SERCA2a. Training also resulted in an 18% lower (P < 0.05) SR Ca(2+) uptake and a 26% lower (P < 0.05) Ca(2+) release. It is concluded that a downregulation in SR Ca(2+) cycling in vastus lateralis occurs with aerobic-based training, which at least in the case of Ca(2+) uptake can be explained by reduction in Ca(2+)-ATPase activity and SERCA1 protein levels.
authors.affiliation: Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1. green@healthy.uwaterloo.ca
authors.forename: H J
authors.initials: HJ
authors.lastname: Green
authors.forename: C S
authors.initials: CS
authors.lastname: Ballantyne
authors.forename: J D
authors.initials: JD
authors.lastname: MacDougall
authors.forename: M A
authors.initials: MA
authors.lastname: Tarnopolsky
authors.forename: J D
authors.initials: JD
authors.lastname: Schertzer
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D015153:Blotting, Western; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000201:enzymology / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000201:enzymology / Q000502:physiology*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases
chemical_list: D009124:Muscle Proteins; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C506943:ATP2A1 protein, human; D000252:Calcium-Transporting ATPases