title: Pattern of summation with fatigue and inhibition of calcium release in rat muscle.
abstract: BACKGROUND
  Fatigue disrupts muscle force summation and is associated with a decrease in cytoplasmic Ca(2+) concentration. The purpose of this study was to compare summation during fatigue and recovery with summation during dantrolene-induced inhibition of Ca(2+) release.
  
  
  METHODS
  Rat medial gastrocnemius muscles were evaluated before and after fatigue, or during exposure to dantrolene. Summation was quantified by the ratio of the force transient associated with the final activation in a train of stimuli (Twf), obtained by subtraction of the force with one less stimulus, and the force of the twitch (Tw).
  
  
  RESULTS
  This ratio (Twf/Tw) decreased from 2.46 ± 0.11 (mean ± SEM) to 0.8 ± 0.1 during intermittent contractions, but was still significantly different from non-fatigued muscle after 10 min of recovery. Dantrolene altered summation, as Twf/Tw was 1.7 ± 0.2 and 1.27 ± 0.15 at a low dose and a high dose, respectively.
  
  
  CONCLUSIONS
  Inhibition of Ca(2+) release alters summation, but repetitive stimulation leading to fatigue changes it more substantially.
authors: Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Alberta T2N 1N4, Canada. brian@kin.ucalgary.ca
authors: Brian R
authors: BR
authors: MacIntosh
authors: Jennifer J
authors: JJ
authors: Glumpak
authors: Meredith B
authors: MB
authors: MacNaughton
authors: Dilson E
authors: DE
authors: Rassier
mesh_terms: D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D003620:Dantrolene / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005260:Female; D023421:Models, Animal; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D009125:Muscle Relaxants, Central / Q000494:pharmacology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D059227:Postsynaptic Potential Summation / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020127:Recovery of Function / Q000502:physiology
chemical_list: D009125:Muscle Relaxants, Central; D003620:Dantrolene; D002118:Calcium