Adaptation of Alpha-Actinin Isoforms to Endurance Exercise Training in Adult and Old Rat Plantaris Muscle

Abstract

We recently reported that that the increase in α-actinin-3 expression was associated with a type I to type II myosin heavy chain (MyHC) shift, and a chronic increase in muscular activity imposed by sprint training enhanced α-actinin-2 expression in rat skeletal muscles (Ogura et al. 2008, 2009). PURPOSE: To clarify the effects of 1) ageing-induced type II to type I MyHC shift and 2) endurance training on the expressions of α-actinin isoforms in rat plantaris muscle. METHODS: Adult (18 mo, n = 12) and old (28 mo, n = 12) male Fischer 344 rats were assigned to either a sedentary or an endurance training group (4 groups, n = 6/each). Animals in the training groups ran on a treadmill for 8 wk. The training intensity was adjusted to be relatively equal for adult and old training groups. After the training program was completed, the plantaris muscles were taken for analyses of α-actinin-2 and α-actinin-3 (western blot), MyHC composition (SDS-PAGE), and citrate synthase (CS) activity (spectrophotometory). Data were analyzed by two-way ANOVA (age × endurance training). RESULTS: Because no interaction was found, data were interpreted with main effect. The proportion of type IIb MyHC was lower (P < 0.05), and that of type I MyHC was higher (P < 0.05) in old animals than in adult animals, suggesting ageing-induced type II to type I MyHC shift. α-Actinin-3 was lower in old animals than in adult animals (adult: 0.97±0.02 vs. old: 0.84 ± 0.04 OD unit, P < 0.05). No significant difference was found in α-actinin-2 and CS activity between adult and old animals. CS activity was higher (+25%, P < 0.05) in trained animals than in sedentary animals. The proportion of type IIb and IIx MyHC were lower (P < 0.05), and that of type IIa MyHC was higher (P < 0.05) in trained animals than in sedentary animals, indicating a fast to slow shift within type II MyHC isoforms by endurance training. α-Actinin-2 was higher in trained animals than in sedentary animals (sedentary: 0.99±0.07 vs. training: 1.40±0.10 OD unit, P < 0.05). No significant difference was found in α-actinin-3 between trained and sedentary animals. CONCLUSIONS: 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.