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

May 13, 2006American journal of physiology. Regulatory, integrative and comparative physiology

Changing carbohydrate intake after long exercise alters muscle calcium storage responses in men

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Abstract

Higher muscle glycogen levels are associated with 36% greater total glycogen at rest in high carbohydrate diets compared to low carbohydrate diets.

Sarcoplasmic reticulum (SR) calcium uptake was 31% higher during high carbohydrate conditions at 30 minutes of exercise compared to low carbohydrate conditions.
Maximal calcium-ATPase activity was 32.8% greater at 30 minutes of exercise in high carbohydrate conditions than in low carbohydrate conditions.
Both phases of calcium release were significantly higher during high carbohydrate diets at 30 and 67 minutes of exercise compared to low carbohydrate diets.
Exercise-induced reductions in SR calcium cycling properties occurred earlier in low glycogen states compared to high glycogen states.
No differences in SR properties were observed at rest between high and low carbohydrate conditions.

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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 (approximately 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 (microM x g protein(-1) x 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 (microM x g protein(-1) x 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.

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

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