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American journal of physiology. Regulatory, integrative and comparative physiology2010; 299(4); R996-R1005; doi: 10.1152/ajpregu.00510.2009

Contractile properties of muscle fibers from the deep and superficial digital flexors of horses.

Abstract: Equine digital flexor muscles have independent tendons but a nearly identical mechanical relationship to the main joint they act upon. Yet these muscles have remarkable diversity in architecture, ranging from long, unipennate fibers ("short" compartment of DDF) to very short, multipennate fibers (SDF). To investigate the functional relevance of the form of the digital flexor muscles, fiber contractile properties were analyzed in the context of architecture differences and in vivo function during locomotion. Myosin heavy chain (MHC) isoform fiber type was studied, and in vitro motility assays were used to measure actin filament sliding velocity (V(f)). Skinned fiber contractile properties [isometric tension (P(0)/CSA), velocity of unloaded shortening (V(US)), and force-Ca(2+) relationships] at both 10 and 30°C were characterized. Contractile properties were correlated with MHC isoform and their respective V(f). The DDF contained a higher percentage of MHC-2A fibers with myosin (heavy meromyosin) and V(f) that was twofold faster than SDF. At 30°C, P(0)/CSA was higher for DDF (103.5 ± 8.75 mN/mm(2)) than SDF fibers (81.8 ± 7.71 mN/mm(2)). Similarly, V(US) (pCa 5, 30°C) was faster for DDF (2.43 ± 0.53 FL/s) than SDF fibers (1.20 ± 0.22 FL/s). Active isometric tension increased with increasing Ca(2+) concentration, with maximal Ca(2+) activation at pCa 5 at each temperature in fibers from each muscle. In general, the collective properties of DDF and SDF were consistent with fiber MHC isoform composition, muscle architecture, and the respective functional roles of the two muscles in locomotion.
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Publication Date: 2010-08-11 PubMed ID: 20702801PubMed Central: PMC2957379DOI: 10.1152/ajpregu.00510.2009Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research explores the different contractile properties of muscle fibers found in the deep and superficial digital flexors of horses. This study seeks to explain how the remarkable architectural diversity among these fibers impacts their functional role during locomotion.

Research Methodology

The digital flexor muscles of horses, despite having differing structures, operate on almost identical mechanical relationships with the main joint they are associated with. The deep digital flexor (DDF) has long unipennate fibers while the superficial digital flexor (SDF) has very short, multipennate fibers. The muscle fibers’ contractile properties were analyzed in two ways:

  • The fiber type was determined through a study of the Myosin heavy chain (MHC) isoform.
  • In-vitro motility assays were used to measure the velocity of actin filament sliding (Vf).

For a more detailed assessment, the skinned fiber contractile properties were characterized at temperatures of 10 and 30 degrees Celsius to understand the isometric tension (P0/CSA), velocity of unloaded shortening (VUS), and force-Ca2+ relationships.

Research Findings

The deep digital flexor (DDF) was discovered to contain a higher percentage of MHC-2A fibers with myosin whose Vf was twice as fast as that of the superficial digital flexor (SDF). At 30 degrees Celsius, parameters such as P0/CSA and VUS were higher and faster respectively for DDF than for SDF fibers. Moreover, an increase in Ca2+ concentration led to an increase in active isometric tension, with maximum activation at pCa 5 at each temperature.

Conclusion

The study concluded that the overall properties of DDF and SDF are influenced by their MHC isoform composition, architectural structure, and the specific functions each type of muscle plays during locomotion. This underlying diversity explains their unique characteristics despite both DD and SDF having similar operational relationships with the main joint they act on. The research provides a comprehensive understanding of the contractile properties and functional differences of these muscle fibers.

Cite This Article

APA
Butcher MT, Chase PB, Hermanson JW, Clark AN, Brunet NM, Bertram JE. (2010). Contractile properties of muscle fibers from the deep and superficial digital flexors of horses. Am J Physiol Regul Integr Comp Physiol, 299(4), R996-R1005. https://doi.org/10.1152/ajpregu.00510.2009

Publication

American journal of physiology. Regulatory, integrative and comparative physiology
ISSN: 1522-1490
NlmUniqueID: 100901230
Country: United States
Language: English
Volume: 299
Issue: 4
Pages: R996-R1005

Researcher Affiliations

Butcher, M T
  • Dept. of Biological Sciences, Youngstown State University, OH 44555, USA. mtbutcher@ysu.edu
Chase, P B
    Hermanson, J W
      Clark, A N
        Brunet, N M
          Bertram, J E A

            MeSH Terms

            • Animals
            • Biomechanical Phenomena
            • Body Temperature / physiology
            • Calcium / physiology
            • Cell Movement
            • Electrophoresis, Polyacrylamide Gel
            • Female
            • Horses / physiology
            • Immunohistochemistry
            • Isometric Contraction
            • Joints / physiology
            • Locomotion / physiology
            • Male
            • Muscle Contraction / physiology
            • Muscle Fibers, Skeletal / chemistry
            • Muscle Fibers, Skeletal / classification
            • Muscle Fibers, Skeletal / physiology
            • Muscle, Skeletal / physiology
            • Myosin Heavy Chains / metabolism
            • Myosins / chemistry
            • Myosins / metabolism
            • Tendons / physiology

            Grant Funding

            • R01 HL063974 / NHLBI NIH HHS
            • R01 HL063974-04 / NHLBI NIH HHS
            • R01 HL063974-05 / NHLBI NIH HHS
            • HL-63974 / NHLBI NIH HHS

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