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MUSCLE CELL BIOLOGY AND CELL MOTILITY

Comparative effects of a low-carbohydrate diet and exercise plus a low-carbohydrate diet on muscle sarcoplasmic reticulum responses in males

Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada

Submitted 22 December 2005 ; accepted in final form 14 April 2006

We employed a glycogen-depleting session of exercise followed by a low-carbohydrate (CHO) diet to investigate modifications that occur in muscle sarcoplasmic reticulum (SR) Ca²⁺-cycling properties compared with low-CHO diet alone. SR properties were assessed in nine untrained males [peak aerobic power (O_{2 peak}) = 43.6 ± 2.6 (SE) ml·kg^–1·min^–1] during prolonged cycle exercise to fatigue performed at 58% O_{2 peak} after 4 days of low-CHO diet (Lo CHO) and after glycogen-depleting exercise plus 4 days of low-CHO (Ex+Lo CHO). Compared with Lo CHO, Ex+Lo CHO resulted in 12% lower (P < 0.05) resting maximal Ca²⁺-ATPase activity (V_max = 174 ± 12 vs. 153 ± 10 µmol·g protein^–1·min^–1) and smaller reduction in V_max induced during exercise. A similar effect was observed for Ca²⁺ uptake. The Hill coefficient, defined as slope of the relationship between cytosolic free Ca²⁺ concentration and Ca²⁺-ATPase activity, was higher (P < 0.05) at rest (2.07 ± 0.15 vs. 1.90 ± 0.10) with Ex+Lo CHO, an effect that persisted throughout the exercise. The coupling ratio, defined as the ratio of Ca²⁺ uptake to V_max, was 23–30% elevated (P < 0.05) at rest and during the first 60 min of exercise with Ex+Lo CHO. The 27 and 34% reductions (P < 0.05) in phase 1 and phase 2 Ca²⁺ release, respectively, observed during exercise with Lo CHO were not altered by Ex+Lo CHO. These results indicate that when prolonged exercise precedes a short-term Lo CHO diet, Ca²⁺ sequestration properties and efficiency are improved compared with those during Lo CHO alone.

calcium cycling; vastus lateralis; contractile activity; glycogen; phosphorylation potential

This article has been cited by other articles:

				T. A. Duhamel, R. D. Stewart, A. R. Tupling, J. Ouyang, and H. J. Green Muscle sarcoplasmic reticulum calcium regulation in humans during consecutive days of exercise and recovery J Appl Physiol, October 1, 2007; 103(4): 1212 - 1220. [Abstract] [Full Text] [PDF]