AI Article Synopsis
- The study explores how different Myosin Heavy Chain (MHC) isoforms affect the muscle fiber properties in pigs, specifically looking at samples from various muscles, including the masseter and diaphragm.
- Researchers used techniques like RT-PCR and gel electrophoresis to isolate and identify four MHC isoforms: slow, 2A, 2X, and 2B, and measured their contractile properties.
- Findings revealed significant differences in maximum shortening velocity (V(o)) and isometric tension (P(o)) across muscle fiber types, with fast fibers showing higher V(o) than anticipated based on body size, highlighting the dominance of fast MHC isoforms in pig muscles.
Article Abstract
Little is known about the influence of Myosin Heavy Chain (MHC) isoforms on the contractile properties of single muscle fibres in large animals. We have studied MHC isoform composition and contractile properties of single muscle fibres from the pig. Masseter, diaphragm, longissimus, semitendinosus, rectractor bulbi and rectus lateralis were sampled in female pigs (aged 6 months, mass 160 kg). RT-PCR, histochemistry, immunohistochemistry and gel electrophoresis were combined to identify and separate four MHC isoforms: MHC-slow and three fast MHC (2A, 2X, 2B). Maximum shortening velocity (V(o)) and isometric tension (P(o)) were measured in single muscle fibres with known MHC isoform composition. Six groups of fibres (pure: slow, 2A, 2X and 2B, and hybrid: 2A-2X and 2X-2B) with large differences in V(o) and P(o) were identified. Slow fibres had mean V(o)=0.17+/-0.01 length s(-1) and P(o)=25.1+/-3.3 mN mm(-2). For fast fibres 2A, 2X and 2B, mean V(o) values were 1.86+/-0.18, 2.55+/-0.19 and 4.06+/-0.33 length s(-1) and mean P(o) values 74.93+/-8.36, 66.85+/-7.58 and 32.96+/-7.47 mN mm(-2), respectively. An in vitro motility assay confirmed that V(o) strictly reflected the functional properties of the myosin isoforms. We conclude that pig muscles express high proportions of fast MHC isoforms, including MHC-2B, and that V(o) values are higher than expected on the basis of the scaling relationship between contractile parameters and body size.
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| http://dx.doi.org/10.1242/jeb.00950 | DOI Listing |
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