Effects of ageing and endurance exercise training on alpha-actinin isoforms in rat plantaris muscle

Aim: We recently reported that alpha-actinin adaptation occurs at the isoform level. This study was undertaken to clarify the effects of: (1) ageing-induced shift of myosin heavy chain (MyHC) composition and (2) endurance exercise training on alpha-actinin isoforms in rat plantaris muscle. Methods: Adult (18 mo) and old (28 mo) male Fischer 344 rats were assigned to either sedentary control or endurance exercise training groups. Animals in the training groups ran on a treadmill for 8 week with training intensity adjusted to be equal for adult and old groups. After the training was completed, the plantaris muscles were taken for analyses of alpha-actinin-2, alpha-actinin-3, and MyHC composition and metabolic enzyme activities. Results: The proportion of type IIb MyHC was lower, and that of type I MyHC was higher in old animals than in adult animals. alpha-actinin-3 was significantly lower in old animals than in adult animals. No significant difference was found in alpha-actinin-2 and citrate synthase (CS) activity between adult and old animals. Citrate synthase activity was higher in trained animals than in sedentary animals. Endurance training produced a fast-to-slow shift within type II MyHC isoforms in both adult and old animals. alpha-actinin-2 was significantly higher in trained animals than in sedentary animals. No significant difference was found in alpha-actinin-3 between trained and sedentary animals. Conclusion: These results support the alpha-actinin adaptation at the isoform level and show that the alpha-actinin-3 expression depends on the amount of type II MyHC, whereas alpha-actinin-2 expression is associated with improvement of muscular aerobic capacity.