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J Appl Physiol (May 18, 2006). doi:10.1152/japplphysiol.00052.2006
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Submitted on January 17, 2006
Accepted on May 15, 2006

Effects of Prior Exercise and a Low Carbohydrate Diet on Muscle Sarcoplasmic Reticulum Function During Cycling in Females

Todd A. Duhamel1, Howard J. Green1*, Jennifer G. Perco1, and Jing Ouyang1

1 Dept. of Kinesiology, University of Waterloo, Waterloo, Canada

* To whom correspondence should be addressed. E-mail: green{at}healthy.uwaterloo.ca.

The effects of exercise and diet on sarcoplasmic reticulum (SR) Ca2+-cycling properties in female vastus lateralis muscle were investigated in 2 groups of females following 4 different conditions. The conditions were 4 days of a low carbohydrate (Lo CHO) and glycogen-depleting exercise plus a Lo CHO diet (Ex + Lo CHO) (Experiment One) and 4 days of normal CHO (Norm CHO) and glycogen-depleting exercise plus Norm CHO (Ex + Norm CHO) (Experiment Two). Peak aerobic power ({nabla}O2peak) was 38.1 ± 1.4 (SE); n=9 and 35.6 ± 1.4 ml.kg-1.min-1; n=9, respectively. SR properties measured in vitro in homogenates (µmoles.protein-1.min-1) indicated exercise-induced reductions (P<0.05) in maximal Ca2+-ATPase activity (0>30, 60 min>fatigue), Ca2+-uptake (0>30>60 min, fatigue) and Ca2+-release, both Phase 1 (0, 30>60 min, fatigue) and Phase 2 (0>30, 60 min, fatigue; 30 min>fatigue) in Norm CHO. Exercise was without effect in altering the Hill slope (nH), defined as the slope of relationship between Ca2+-ATPase activity and Ca2+-concentration. No differences were observed between Norm CHO and Ex+Norm CHO. When compared to Norm CHO, Lo CHO resulted in a lower (P<0.05) Ca2+-uptake, Phase 1 Ca2+-release (30 min) and nH. Ex + Lo CHO resulted in a greater (P<0.05) Ca2+-uptake and nH compared to Lo CHO. The results demonstrate that Lo CHO alone can disrupt SR Ca2+-cycling and that with the exception of Ca2+-release, a glycogen-depleting session of exercise prior to Lo CHO can reverse the effects.




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