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Am J Physiol Regul Integr Comp Physiol 291: R1100-R1110, 2006. First published May 11, 2006; doi:10.1152/ajpregu.00858.2005
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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Manipulation of dietary carbohydrates after prolonged effort modifies muscle sarcoplasmic reticulum responses in exercising males

T. A. Duhamel, J. G. Perco, and H. J. Green

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

Submitted 7 December 2005 ; accepted in final form 10 May 2006

The hypothesis tested was that disturbances in the sarcoplasmic reticulum (SR) Ca2+-cycling responses to exercise would associate with muscle glycogen reserves. Ten untrained males [peak O2 consumption (VO2 peak) = 3.41 ± 0.20 (SE) l/min] performed a standardized cycle test (~70% VO2 peak) on two occasions, namely, following 4 days of a high (Hi CHO)- and 4 days of a low (Lo CHO)-carbohydrate diet. Both Hi CHO and Lo CHO were preceded by a session of prolonged exercise designed to deplete muscle glycogen. SR Ca2+ cycling in crude homogenates prepared from vastus lateralis samples indicated higher (P < 0.05) Ca2+ uptake (µM·g protein–1·min–1) in Hi CHO compared with Lo CHO at 30 min (2.93 ± 0.10 vs. 2.23 ± 0.12) and at 67 min (2.77 ± 0.16 vs. 2.10 ± 0.12) of exercise, the point of fatigue in Lo CHO. Similar effects (P < 0.05) were noted between conditions for maximal Ca2+-ATPase (µM·g protein–1·min–1) at 30 min (142 ± 8.5 vs. 107 ± 5.0) and at 67 min (130 ± 4.5 vs. 101 ± 4.7). Both phase 1 and phase 2 Ca2+ release were 23 and 37% higher (P < 0.05) at 30 min of exercise and 15 and 34% higher (P < 0.05), at 67 min during Hi CHO compared with Lo CHO, respectively. No differences between conditions were observed at rest for any of these SR properties. Total muscle glycogen (mmol glucosyl units/kg dry wt) was higher (P < 0.05) in Hi CHO compared with Lo CHO at rest (+36%), 30 min (+53%), and at 67 min (+44%) of cycling. These results indicate that exercise-induced reductions in SR Ca2+-cycling properties occur earlier in exercise during low glycogen states compared with high glycogen states.

calcium ion regulation; diet


Address for reprint requests and other correspondence: H. J. Green, Dept. of Kinesiology, Univ. of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (e-mail: green{at}healthy.uwaterloo.ca)




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