Different adaptations of alpha‐actinin isoforms to exercise training in rat skeletal muscles

Aim: Alpha (α)‐actinins are located in the skeletal muscle Z‐line and form actin–actin cross‐links. Mammalian skeletal muscle has two isoforms: α‐actinin‐2 and α‐actinin‐3. However, the response of α‐actinin to exercise training is little understood. Therefore, the current study examined the effects of exercise training on the expression level of two α‐actinin isoforms in skeletal muscles. Methods: Twelve male Wistar rats were assigned randomly to a control (C; n = 6) or exercise training (T; n = 6) group. After T animals were trained on an animal treadmill for 9 weeks, α‐actinin‐2 and α‐actinin‐3 levels in the plantaris, white and red gastrocnemius muscles were analysed. In addition, changes in the myosin heavy chain (MyHC) composition were assessed, and muscle bioenergetic enzyme activities were measured. Results: Results show that exercise training increased α‐actinin‐2 expression levels in all muscles (P < 0.05). However, no significant difference was found in α‐actinin‐3 expression levels between C and T animals. Subsequent MyHC analyses of all muscle showed an MyHC shift with direction from IIb to IIa. Furthermore, enzymatic analysis revealed that exercise training improved enzyme activities related to aerobic metabolism. Conclusion: The results of this study demonstrate that exercise training alters the expression level of α‐actinin at the isoform level. Moreover, the increase in expression levels of α‐actinin‐2 is apparently related to alteration of skeletal muscle: its aerobic capacity is improved.