Measuring Mechanical Properties, Including Isotonic Fatigue, of Fast and Slow MLC/mIgf-1 Transgenic Skeletal Muscle
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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.
KeywordsTransgenic muscle Twitch force Isometric and isotonic force Hill’s equation Muscle power measurement Muscle isotonic fatigue measurement
The authors wish to thank professor Peter Grigg for invaluable discussions about muscle physiology and for polishing the English of the manuscript, and professor Mario Molinaro for his continuous encouragements during the experiments. This research was partially supported by Telethon (grant n. GSP030543) and MDA (grant no. 3986).
- 26.Hill A. V. 1938 The heat of shortening and the dynamic constants of muscle. Proc. R. Soc. Lond. Ser. B 126:136–195Google Scholar
- 37.Musarò A., C. Giacinti, G. Borsellino, G. Dobrowolny, L. Pelosi, L. Cairns, S. Ottolenghi, G. Bernardi, G. Cossu, L. Battistini, et al. 2004 Muscle restricted expression of mIGF-1 enhances the recruitment of stem cells during muscle regeneration. Proc. Natl. Acad. Sci. USA 101:1206–1210PubMedCrossRefGoogle Scholar