Measuring mechanical properties, including isotonic fatigue, of fast and slow MLC/mIgf-1 transgenic skeletal muscle.
Contractile properties of fast-twitch (EDL) and slow-twitch (soleus) skeletal muscles were measured in MLC/mIgf-1 transgenic and wild-type mice. MLC/mIgf-1 mice express the local factor mIgf-1 under the transcriptional control of MLC promoter, selectively activated in fast-twitch muscle fibers. Isolated muscles were studied in vitro in both isometric and isotonic conditions. We used a rapid "ad hoc" testing protocol that measured, in a single procedure, contraction time, tetanic force, Hill's (F-v) curve, power curve and isotonic muscle fatigue. Transgenic soleus muscles did not differ from wild-type with regard to any measured variable. In contrast, transgenic EDL muscles displayed a hypertrophic phenotype, with a mass increase of 29.2% compared to wild-type. Absolute tetanic force increased by 21.5% and absolute maximum power by 34.1%. However, when normalized to muscle cross-sectional area and mass, specific force and normalized power were the same in transgenic and wild-type EDL muscles, revealing that mIgf-1 expression induces a functional hypertrophy without altering fibrotic tissue accumulation. Isotonic fatigue behavior did not differ between transgenic and wild-type muscles, suggesting that the ability of mIgf-1 transgenic muscle to generate a considerable higher absolute power did not affect its resistance to fatigue.
Del Prete
Zaccaria
Z
Department of Mechanical and Aeronautical Engineering, University of Rome La Sapienza, Via Eudossiana, 18, 00184, Rome, Italy. zaccaria.delprete@uniroma1.it
Musarò
Antonio
A
Rizzuto
Emanuele
E
D000818:Animals; D030801:Animals, Genetically Modified; D001696:Biomechanical Phenomena / Q000295:instrumentation / Q000379:methods*; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D008297:Male; D051379:Mice; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D018994:Myosin Light Chains / Q000502:physiology*
D018994:Myosin Light Chains; D007334:Insulin-Like Growth Factor I