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

We recently reported that α-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 α-actinin isoforms in rat plantaris muscle.

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 α-actinin-2, α-actinin-3, and MyHC composition and metabolic enzyme activities.

The proportion of type IIb MyHC was lower, and that of type I MyHC was higher in old animals than in adult animals. α-actinin-3 was significantly lower in old animals than in adult animals. No significant difference was found in α-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. α-actinin-2 was significantly higher in trained animals than in sedentary animals. No significant difference was found in α-actinin-3 between trained and sedentary animals.

These results support the α-actinin adaptation at the isoform level and show that the α-actinin-3 expression depends on the amount of type II MyHC, whereas α-actinin-2 expression is associated with improvement of muscular aerobic capacity.