title: Single Muscle Immobilization Decreases Single-Fibre Myosin Heavy Chain Polymorphism: Possible Involvement of p38 and JNK MAP Kinases.
abstract: OBJECTIVE
  Muscle contractile phenotype is affected during immobilization. Myosin heavy chain (MHC) isoforms are the major determinant of the muscle contractile phenotype. We therefore sought to evaluate the effects of muscle immobilization on both the MHC composition at single-fibre level and the mitogen-activated protein kinases (MAPK), a family of intracellular signaling pathways involved in the stress-induced muscle plasticity.
  
  
  METHODS
  The distal tendon of female Wistar rat Peroneus Longus (PL) was cut and fixed to the adjacent bone at neutral muscle length. Four weeks after the surgery, immobilized and contralateral PL were dissociated and the isolated fibres were sampled to determine MHC composition. Protein kinase 38 (p38), extracellular signal-regulated kinases (ERK1/2), and c-Jun- NH2-terminal kinase (JNK) phosphorylations were measured in 6- and 15-day immobilized and contralateral PL.
  
  
  RESULTS
  MHC distribution in immobilized PL was as follows: I = 0%, IIa = 11.8 ± 2.8%, IIx = 53.0 ± 6.1%, IIb = 35.3 ± 7.3% and I = 6.1 ± 3.9%, IIa = 22.1 ± 3.4%, IIx = 46.6 ± 4.5%, IIb = 25.2 ± 6.6% in contralateral muscle. The MHC composition in immobilized muscle is consistent with a faster contractile phenotype according to the Hill's model of the force-velocity relationship. Immobilized and contralateral muscles displayed a polymorphism index of 31.1% (95% CI 26.1-36.0) and 39.3% (95% CI 37.0-41.5), respectively. Significant increases in p38 and JNK phosphorylation were observed following 6 and 15 days of immobilization.
  
  
  CONCLUSIONS
  Single muscle immobilization at neutral length induces a shift of MHC composition toward a faster contractile phenotype and decreases the polymorphic profile of single fibres. Activation of p38 and JNK could be a potential mechanism involved in these contractile phenotype modifications during muscle immobilization.
authors.affiliation: Laboratory "Movement Sport and health Sciences"(M2S) -EA1274, University Rennes 2-ENS Rennes, Rennes, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Derbré
authors.affiliation: Physiology Department-EA1274 M2S, School of Medicine, Brest, France.
authors.forename: Mickaël
authors.initials: M
authors.lastname: Droguet
authors.affiliation: Physiology Department-EA1274 M2S, School of Medicine, Brest, France.
authors.forename: Karelle
authors.initials: K
authors.lastname: Léon
authors.affiliation: Physiology Department-EA1274 M2S, School of Medicine, Brest, France.
authors.forename: Samuel
authors.initials: S
authors.lastname: Troadec
authors.affiliation: Physiology Department-EA1274 M2S, School of Medicine, Brest, France.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Pennec
authors.affiliation: Physiology Department-EA1274 M2S, School of Medicine, Brest, France.
authors.forename: Marie-Agnès
authors.initials: MA
authors.lastname: Giroux-Metges
authors.affiliation: Physiology Department-EA1274 M2S, School of Medicine, Brest, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Rannou
mesh_terms: D000818:Animals; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D015151:Immunoblotting; D066298:In Vitro Techniques; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D018995:Myosin Heavy Chains / Q000378:metabolism* / Q000502:physiology; D010766:Phosphorylation; D020033:Protein Isoforms / Q000378:metabolism / Q000502:physiology; D017208:Rats, Wistar; D013997:Time Factors; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D018995:Myosin Heavy Chains