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1 St.Boniface General Hospital Research Centre, University of Manitoba, Winnipeg, Canada
2 Department of Kinesiology, University of Waterloo, Waterloo, Canada
3 Department of Kinesiology, University of Waterloo, Canada
* To whom correspondence should be addressed. E-mail: green{at}healthy.uwaterloo.ca.
The study investigated the hypothesis that 3 consecutive days of prolonged cycle exercise would result in a sustained reduction in the Ca2+-cycling properties of the vastus lateralis in the absence of changes in the sarcoplasmic (endoplasmic) reticulum Ca2+-ATPase (SERCA) protein. Tissue samples were obtained at pre (Pre) and post (Post) exercise on day 1 (E1) and day 3 (E3) and during recovery days 1 (R1), 2 (R2) and 3 (R3) in 12 active but untrained volunteers (age 19.2 ± 0.27 yr; mean±SE) and analyzed for changes (nmol.mg protein-1.min-1) in maximal Ca2+-ATPase activity (Vmax), Ca2+-uptake and Ca2+-release (Phase 1 and Phase 2) and SERCA isoform expression (SERCA1a and SERCA2a). At E1, reductions (P<0.05) from Pre to Post in Vmax (150±7 vs 121±7), Ca2+-uptake (7.79±0.28 vs 5.71±0.33) and both phases of Ca2+-release (Phase 1, 20.3±1.3 vs 15.2±1.1; Phase 2, 7.70±0.60 vs 4.99±0.48) were found. In contrast to Vmax, which recovered at Pre E3 and then remained stable at Post E3 and throughout recovery, Ca2+-uptake remained depressed (P<0.05) at E3 Pre and Post and at R1 as did Phase 2 of Ca2+-release. Exercise resulted in an increase (P<0.05) in SERCA1a (14% at R2) but not SERCA2a. It is concluded that rapidly adapting mechanisms protect Vmax following the onset of regular exercise but not Ca2+-uptake and Ca2+-release.
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