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Revisiting the peculiar regional distribution of muscle fiber types in rat Sternomastoid Muscle

Barbara Ravara, Valerio Gobbo, Damiana Incendi, Andrea Porzionato, Veronica Macchi, Raffaele De Caro, Dario Coletti, Tiziana Martinello, Marco Patruno
  • Barbara Ravara
    Laboratory of Translational Myology, Department of Biomedical Sciences, University of Padova; Interdepartmental Research Center of Myology (CIR-Myo), University of Padova; A&C M-C Foundation for Translational Myology, Padova, Italy | barbara.ravara@unipd.it
  • Valerio Gobbo
    CNR Institute of Neuroscience, Padova, Italy
  • Damiana Incendi
    Human Anatomy Section of the Department of Neurosciences, University of Padova, Italy
  • Andrea Porzionato
    Interdepartmental Research Center of Myology (CIR-Myo), University of Padova; Human Anatomy Section of the Department of Neurosciences, University of Padova, Italy
  • Veronica Macchi
    Human Anatomy Section of the Department of Neurosciences, University of Padova, Italy
  • Raffaele De Caro
    Human Anatomy Section of the Department of Neurosciences, University of Padova, Italy
  • Dario Coletti
    Sorbonne Universités, UPMC Univ Paris 06 (CNRS, UMR 8256, INSERM ERL U1164), Institut Biologie Paris-Seine, Paris, France; Department of Anatomy, Histology, Forensic Medicine & Orthopedics, School of Medicine Sapienza University of Rome, Italy; Interuniversity Institute of Myology, Italy, Italy
  • Tiziana Martinello
    Interdepartmental Research Center of Myology (CIR-Myo), University of Padova; Department of Comparative Biomedicine and Food Science, University of Padova, Italy
  • Marco Patruno
    Interdepartmental Research Center of Myology (CIR-Myo), University of Padova; Department of Comparative Biomedicine and Food Science, University of Padova, Italy

Abstract

The sternomastoid (SM) muscle in rodents is known to have a peculiar distribution of fiber types with a steep gradient from surface to deep region. We here further characterize this peculiar regional distribution by quantitative histochemical morphometrys. In Hematoxylin-Eosin (H-E) stained transverse cryosections harvested in the medial portion of the muscle we counted around 10.000 myofibers with a mean diameter of 51.3±12.6 (μm). Cryisections of the SM stained by SDH reaction clearly show two distinct regions, toward the deep surface of the muscle a 40% area that contains packed SDH-positive myofibers, while the remaining area of the SM toward the external surface presents a more checker-board appearance. On the other hand, in the deep region of SM type 1 (slow contracting) muscle fibers, caracterized by positive acidic ATPase pH 4.35 reaction, are only the 24.5% of the fibers in the deep area of SM muscles, being restricted to the deepest region. The 75.5% of the myofibers in the deep region are of the fast contracting types (either 48.4% 2A, SDH –positive fibers or 27.1% 2B, SDH-negative fibers, respectively). As expected the 2B muscle fibers, acidic ATPase pH 4.3-negative and SDH-negative, present the largest size, while Type 1 fibers, acidic ATPase pH 4.3-positive and SDH-positive, present the smallest size in rat SM muscle. Based on present and previous observations, comparison of change in absolute number and/or percentage of the fiber types in any experimental model of muscle atrophy/hypertrophy/plasticity/pathology /recovery in the rat SM, and possibly of all mammals, will ask for morphometry of the whole muscle cross-sections, muscle sampling by bioptic approches will provide only comparable data on the size of the different types of muscle fibers.

Keywords

rat, Sternomastoid muscle, muscle fiber types, SDH, myofibrillar ATPases, regional distribution

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Submitted: 2018-01-15 12:43:35
Published: 2018-03-01 12:13:24
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