title: Differential susceptibility of muscles to myotonia and force impairment in a mouse model of myotonic dystrophy.
abstract: BACKGROUND
  Myotonic dystrophy, or dystrophia myotonica (DM), is characterized by prominent muscle wasting and weakness as well as delayed muscle relaxation resulting from persistent electrical discharges.
  
  
  METHODS
  We hypothesized heterogeneity among muscles in degree of weakness and myotonia in an expanded [(CUG)(250)] repeats transgenic (HSA(LR)) mouse DM model. Muscle contraction was compared among diaphragm, extensor digitorum longus (EDL), and soleus muscles.
  
  
  RESULTS
  Myotonia was found only in EDL, as manifested by longer late-relaxation time and elevated myotonic index. EDL, but not the other two muscles, had impaired force over a wide range of stimulation frequencies. During fatigue-inducing stimulation, DM EDL muscle force per cross-sectional area was significantly impaired during 25-Hz stimulation, whereas there were no differences in fatigue response for DM diaphragm or soleus.
  
  
  CONCLUSIONS
  In an expanded repeats model of DM the EDL is more susceptible to myotonia and force impairment than muscles with lower proportions of fast-twitch fibers.
authors.affiliation: Department of Medicine, Division of Pulmonary, Critical Care and Sleep, Cleveland VA Medical Center, K201, 10701 East Boulevard, Cleveland, Ohio 44106, USA.
authors.forename: Michelle
authors.initials: M
authors.lastname: Moyer
authors.forename: Dara S
authors.initials: DS
authors.lastname: Berger
authors.forename: Andrea N
authors.initials: AN
authors.lastname: Ladd
authors.forename: Erik
authors.initials: E
authors.lastname: Van Lunteren
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D051379:Mice; D008822:Mice, Transgenic; D009119:Muscle Contraction / Q000235:genetics; D053580:Muscle Strength / Q000235:genetics; D018908:Muscle Weakness / Q000175:diagnosis / Q000235:genetics* / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009223:Myotonic Dystrophy / Q000175:diagnosis / Q000235:genetics* / Q000503:physiopathology*; D019680:Trinucleotide Repeat Expansion / Q000235:genetics