Exercise training‐induced adaptations associated with increases in skeletal muscle glycogen content

Abstract

Chronic exercise training results in numerous skeletal muscle adaptations, including increases in insulin sensitivity and glycogen content. To understand the mechanism for increased muscle glycogen, we studied the effects of exercise training on glycogen regulatory proteins in rat skeletal muscle. Female Sprague Dawley rats performed voluntary wheel running for 1, 4, or 7 weeks. After 7 weeks of training, insulin-stimulated glucose uptake was increased in epitrochlearis muscle. Compared to sedentary control rats, muscle glycogen did not change after 1 week of training, but increased significantly after 4 and 7 weeks. The increases in muscle glycogen were accompanied by elevated glycogen synthase activity and protein expression. To assess the regulation of glycogen synthase, we examined its major activator, protein phosphatase 1 (PP1), and its major deactivator, glycogen synthase kinase 3 (GSK3). Consistent with glycogen synthase activity, PP1 activity was unchanged after 1 week of training but significantly increased after 4 and 7 weeks of training. Protein expression of RGL(GM), another regulatory PP1 subunit, significantly decreased after 4 and 7 weeks of training. Unlike PP1, GSK3 phosphorylation did not follow the pattern of glycogen synthase activity. The ~40% decrease in GSK-3α phosphorylation after 1 week of exercise training persisted until 7 weeks and may function as a negative feedback to elevated glycogen. Our findings suggest that exercise training-induced increases in muscle glycogen content could be regulated by multiple mechanisms including enhanced insulin sensitivity, glycogen synthase expression, allosteric activation of glycogen synthase and PP1activity.

Gestational exercise protects adult male offspring from high-fat diet-induced hepatic steatosis

“…Healthy female rats commonly run >10 km/day [46], and previous reports by our group [6, 9] indicate that providing access to running wheels 7 to 10 days prior to pregnancy resulted in the exercise trained dams averaging ~4.5 km/day during pregnancy. This is in contrast to the current report, where wheel access beginning at day 4 of gestation resulted in much lower total volume of activity and lower average daily running distance (~2.5km/day).…”

CD36 is essential for endurance improvement, changes in whole-body metabolism, and efficient PPAR-related transcriptional responses in the muscle with exercise training

“…; Manabe et al. ). The absence of CD36 did not impair nor improve skeletal muscle glycogen accumulation with training.…”

Gender-dependent differences of mitochondrial function and oxidative stress in rat skeletal muscle at rest and after exercise training

“…In female Sprague-Dawley rats, endurance training of about 20 days increased maximal mitochondrial respiration in the soleus muscle but not in the gastrocnemius muscle [34]. In the same rat strain, Manabe et al [35] showed that training induces increased muscular glycogen content in female rats.…”