title: Malleability of human skeletal muscle sarcoplasmic reticulum to short-term training.
abstract: This study investigated the hypothesis that adaptations would occur in the sarcoplasmic reticulum in vastus lateralis soon after the onset of aerobic-based training consistent with reduced Ca²⁺-cycling potential. Tissue samples were extracted prior to (0 days) and following 3 and 6 days of cycling performed for 2 h at 60%-65% of peak aerobic power (VO₂(peak)) in untrained males (VO₂(peak) = 47 ± 2.3 mL·kg⁻¹·min⁻¹; mean ± SE, n = 6) and assessed for changes (nmol·mg protein⁻¹·min⁻¹) in maximal Ca²⁺-ATPase activity (V(max)), Ca²⁺-uptake, and Ca²⁺-release (phase 1 and phase 2) as well as the sarcoplasmic (endoplasmic) reticulum Ca²⁺-ATPase (SERCA) isoforms. Training resulted in reductions (p < 0.05) in SERCA1a at 6 days (-14%) but not at 3 days. For SERCA2a, reductions (p < 0.05) were also noted only at 6 days (-7%). For V(max), depressions (p < 0.05) were found at 6 days (172 ± 11) but not at 3 days (176 ± 13; p < 0.10) compared with 0 days (192 ± 11). These changes were accompanied by a lower (p < 0.05) Ca²⁺-uptake at both 3 days (-39%) and 6 days (-48%). A similar pattern was found for phase 1 Ca²⁺-release with reductions (p < 0.05) of 37% observed at 6 days and 23% (p = 0.21) at 3 days of training, respectively. In a related study using the same training protocol and participant characteristics, microphotometric determinations of V(max) indicated reductions (p < 0.05) in type I at 3 days (-27%) and at 6 days (-34%) and in type IIA fibres at 6 days (-17%). It is concluded that in response to aerobic-based training, sarcoplasmic reticulum Ca²⁺-cycling potential is reduced by adaptations that occur soon after training onset.
authors.affiliation: Department of Kinesiology, University of Waterloo, Waterloo, ON N2L3G1 Canada. green@uwaterloo.ca
authors.forename: Howard J
authors.initials: HJ
authors.lastname: Green
authors.forename: Margaret
authors.initials: M
authors.lastname: Burnett
authors.forename: Helen
authors.initials: H
authors.lastname: Kollias
authors.forename: Jing
authors.initials: J
authors.lastname: Ouyang
authors.forename: Ian
authors.initials: I
authors.lastname: Smith
authors.forename: Susan
authors.initials: S
authors.lastname: Tupling
mesh_terms: D000328:Adult; D001642:Bicycling; D020013:Calcium Signaling; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D015536:Down-Regulation; D015444:Exercise; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism; D010101:Oxygen Consumption; D052097:Quadriceps Muscle / Q000201:enzymology / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000201:enzymology / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C506943:ATP2A1 protein, human; C506946:ATP2A2 protein, human; D000252:Calcium-Transporting ATPases