Article

Annals of Biomedical Engineering

, 36:1281

First online:

Measuring Mechanical Properties, Including Isotonic Fatigue, of Fast and Slow MLC/mIgf-1 Transgenic Skeletal Muscle

  • Zaccaria Del PreteAffiliated withDepartment of Mechanical and Aeronautical Engineering, University of Rome “La Sapienza” Email author 
  • , Antonio MusaròAffiliated withDepartment of Histology and Medical Embryology, IIM, University of Rome “La Sapienza”
  • , Emanuele RizzutoAffiliated withDepartment of Histology and Medical Embryology, IIM, University of Rome “La Sapienza”

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Abstract

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 (Fv) 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.

Keywords

Transgenic muscle Twitch force Isometric and isotonic force Hill’s equation Muscle power measurement Muscle isotonic fatigue measurement