Contraction mode itself does not determine the level of mTORC1 activity in rat skeletal muscle.
Resistance training with eccentric contraction has been shown to augment muscle hypertrophy more than other contraction modes do (i.e., concentric and isometric contraction). However, the molecular mechanisms involved remain unclear. The purpose of this study was to investigate the effect of muscle contraction mode on mammalian target of rapamycin complex 1 (mTORC1) signaling using a standardized force-time integral (load (weight) × contraction time). Male Sprague-Dawley rats were randomly assigned to three groups: eccentric contraction, concentric contraction, and isometric contraction. The right gastrocnemius muscle was exercised via percutaneous electrical stimulation-induced maximal contraction. In experiment 1, different modes of muscle contraction were exerted using the same number of reps in all groups, while in experiment 2, muscle contractions were exerted using a standardized force-time integral. Muscle samples were obtained immediately and 3 h after exercise. Phosphorylation of molecules associated with mTORC1 activity was assessed using western blot analysis. In experiment 1, the force-time integral was significantly different among contraction modes with a higher force-time integral for eccentric contraction compared to that for other contraction modes (P < 0.05). In addition, the force-time integral was higher for concentric contraction compared to that for isometric contraction (P < 0.05). Similarly, p70S6K phosphorylation level was higher for eccentric contraction than for other modes of contraction (P < 0.05), and concentric contraction was higher than isometric contraction (P < 0.05) 3 h after exercise. In experiment 2, under the same force-time integral, p70S6K (Thr389) and 4E-BP1 phosphorylation levels were similar among contraction modes 3 h after exercise. Our results suggest that mTORC1 activity is not determined by differences in muscle contraction mode itself. Instead, mTORC1 activity is determined by differences in the force-time integral during muscle contraction.
Faculty of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan.
Satoru
S
Ato
Faculty of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan.
Yuhei
Y
Makanae
Faculty of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan.
Kohei
K
Kido
Faculty of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan safujita@fc.ritsumei.ac.jp.
Satoshi
S
Fujita
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes / Q000378:metabolism*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D010805:Physical Conditioning, Animal / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D055070:Resistance Training; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
D002352:Carrier Proteins; C499526:Eif4ebp1 protein, rat; D047908:Intracellular Signaling Peptides and Proteins; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D000076222:Mechanistic Target of Rapamycin Complex 1; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases
Mammalian target of rapamycin complex 1; muscle contraction mode; resistance exercise
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