Differences in exercise capacity and muscle glycogen metabolism in C57BL/6J and BALB/cA mice

This study compared differences in exercise capacity as well as muscle glycogen content and degradation, and mitochondrial enzyme activity between C57BL/6J and BALB/cA mice. In exercise tests, grip strength was higher in BALB/cA mice. In Rotarod and Inverted screen test, C57BL/6J mice had significantly longer exercise durations and showed differences in motor function and muscle endurance time. Glycogen in the liver and muscle of C57BL/6J mice was significantly decreased after 20 min of swimming. Muscle glycogen content in BALB/cA mice was higher than in C57BL/6J, but swimming induced no decrease in glycogen content. Glycogen phosphorylase in muscle was inactive in the absence of AMP, and its activity increased in a concentration-dependent manner with the addition of AMP in C57BL/6J mice. In BALB/cA mice, phosphorylase activity was increased by AMP, but not further increased by higher concentrations of AMP. The citrate synthase activity in muscle did not differ between C57BL/6J and BALB/cA mice. The results of this study suggested that the reactivity of muscle glycogen phosphorylase to AMP differs among strains of mice and affects glycogen availability during exercise.