Neda khaledi^1,, Rana Fayazmilani², Abbas Ali Gaeini³, Arash Javeri⁴

Purpose: Mammalian skeletal muscle has the two isoforms of actin binding protein, α-Actinin-2 and α-Actinin-3, which are located in the skeletal muscle Z-line where they cross-link the actin thin filaments. There is a common stop codon polymorphism R577X in the ACTN3 gene. Several association studies have demonstrated that the ACTN3 R577X genotype influences athletic performance. The response of α-Actinins to resistance exercise training is little understood. Methods: Female Sprague-Dawley rats were assigned to control (C; n = 10) and resistance training (T; n = 12) groups. Training consisted of climbing a ladder carrying a load suspended from the tail. After training, fast (Flexor halluces longus, FHL) and slow (Soleus) hind limb muscles from each group was examine to study the effect of resistance training on muscle mass. Gene expression and protein levels of both Actn3, Actn2 were examined. Results: The resistance trained group had a significantly greater absolute muscle mass in FHL (P=0.011). We also found that Actn3 and Actn2 gene expression levels increased significantly in FHL and Soleus muscles by mean factors of 2.16, and 2.91, respectively. α-Actinin-2 protein expression increased significantly in training group (P=0.025) while, α-actinin-3 protein expression remained similar in training & control groups (P=0.130). The most important finding of this study showed that both α-actinin-3 and α-actinin-2 mRNA levels were up-regulated after 8wk of resistance training (P≤0.05). Conclusion: Our results provide a new insight into the impact of progressive resistance training and evaluating the role of α-actinins responsiveness.

vertical ladder, α–actinins, sarcomere, Z-line, resistance training