title: Fatigue-inducing stimulation resolves myotonia in a drug-induced model.
abstract: BACKGROUND
  Slowed muscle relaxation is the contractile hallmark of myotonia congenita, a disease caused by genetic CLC-1 chloride channel deficiency, which improves with antecedent brief contractions ("warm-up phenomenon"). It is unclear to what extent the myotonia continues to dissipate during continued repetitive contractions and how this relates temporally to muscle fatigue. Diaphragm, EDL, and soleus muscles were examined in vitro during repetitive 20 Hz and 50 Hz train stimulation in a drug-induced (9-AC) rat myotonia model.
  
  
  RESULTS
  At the onset of stimulation, 9-AC treated diaphragm and EDL muscle had markedly prolonged half relaxation and late relaxation times (range 147 to 884 ms, 894 to 1324 ms). Half relaxation and late relaxation times reached near-normal values over the 5-10 and 10-40 subsequent contractions, respectively. In both muscles myotonia declined faster during repetitive 50 Hz than 20 Hz stimulation, and much faster than the rate of force loss during fatigue at both frequencies. Soleus muscle was resistant to the myotonic effects of 9-AC.
  
  
  CONCLUSIONS
  In a drug-induced model of mechanical myotonia, fatigue-inducing stimulation resolves the myotonia, which furthermore appears to be independent from the development of muscle fatigue.
authors.affiliation: Pulmonary and Critical Care Medicine, Case Western Reserve University and Louis Stokes Cleveland Department of Veterans Affairs, Cleveland, OH 44106, USA. exv4@cwru.edu
authors.forename: Erik
authors.initials: E
authors.lastname: van Lunteren
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Spiegler
authors.forename: Michelle
authors.initials: M
authors.lastname: Moyer
mesh_terms: D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D018118:Chloride Channels / Q000172:deficiency; D003964:Diaphragm / Q000187:drug effects / Q000502:physiology; D004558:Electric Stimulation; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects / Q000502:physiology; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology; D009222:Myotonia / Q000139:chemically induced* / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000873:Anthracenes; C086321:CLC-1 channel; D018118:Chloride Channels; C010030:9-anthroic acid