Proceedings of The Physiological Society
University of Manchester (2010) Proc Physiol Soc 19, PC63
Effects of lengthening contraction velocity on protein synthesis/degradation signal pathways in rat medial gastrocnemius muscle
E. Ochi1, T. Hirose3, K. Hiranuma2, A. Tsutaki2, S. Min2, N. Ishii4, K. Nakazato2
1. Laboratory of Health & Sports Sciences, Meiji Gakuin Univ., Yokohama,, Japan. 2. Graduate School of Sport Science, Nippon Sport Science University, Tokyo, Japan. 3. Department of Culture and Sport Policy, Toin University of Yokohama, Yokohama, Japan. 4. Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Tokyo, Japan.
The purpose of this study was to investigate the effects of lengthening contractions (LCs) on protein synthesis and/or protein degradation signaling pathways after contraction-induced muscle injury. We employed our originally developed device with two LC modes to modulate the intensity of LCs in rat gastrocnemius muscle (Ochi et al., 2010a,b). Since high LC velocity causes severe muscle damage, we speculated that the protein degradation signaling pathway is activated by fast LCs. Male Wistar rats (n=36) were randomly divided into fast velocity LCs group(FAST, 180deg/s, n=12), slow LCs group(SLOW, 30deg/s, n=12), and control group (control, n=12). The FAST and SLOW rats were anesthetized with isoflurane (air flow rate, 450ml/min, concentration, 2.0%). The triceps surae muscle of the right hindlimb was then electrically stimulated with forced isokinetic dorsi-flexion (30°/s and from 0 to 45°). The control group was anesthetized only and received no other treatment. The torque was measured before and after LCs. Tissue contents of Akt(P), mTOR(P), P70S6k(P), FOXO1(P), FOXO3(P), myostatin, and ActRIIB were measured by western blotting. This study was approved by the Ethical Committee for Animal Experiments at the Nippon Sport Science University. Two-way ANOVA followed by Bonferroni was used(time vs. groups). No significant changes were observed in both body mass and hindlimb muscles between the groups. The torque after LCs was significantly lower in FAST than in SLOW (days 1, 3, and 5, P < 0.05; day 2, P < 0.01). Akt(P) in SLOW, but not in FAST, was significantly higher than that in the control (Fig. 1). There was no significant difference in mTOR(P) between the groups. P70S6k (P) on days 2 and 7 in SLOW were significantly higher than that in the control, and P70S6k (P) on day 7 in SLOW was also significantly higher than that in FAST on day 7 and SLOW on day 2 (P < 0.05). FOXO1 and FOXO3 on both days 2 and 7 showed significantly enhanced expression in FAST than in the other two period-matched groups (Fig. 2). The muscle content of myostatin on days 2 and 7 was significantly higher in FAST than in the other 2 period-matched groups (P < 0.001), while that of ActRIIB was significantly lower in SLOW than in the other two groups. These results suggest that fast LCs cause a decrease in muscular strength and activation of the protein degradation signaling pathways, while the protein synthesis signaling pathways are activated after slow LCs. We conclude that the velocities of LCs are related to the severity of muscle damage and that prolonged torque deficit is associated with activation of the protein degradation process.
Where applicable, experiments conform with Society ethical requirements