title: Contractile properties of slow and fast skeletal muscles from protease activated receptor-1 null mice.
abstract: BACKGROUND
  Protease-activated receptors (PARs) may play a role in skeletal muscle development. We compared the contractile properties of slow-twitch soleus muscles and fast-twitch extensor digitorum longus (EDL) muscles from PAR-1 null and littermate control mice.
  
  
  METHODS
  Contractile function was measured using a force transducer system. Fiber type proportions were determined using immunohistochemistry.
  
  
  RESULTS
  Soleus muscles from PAR-1 null mice exhibited longer contraction times, a leftward shift in the force-stimulation frequency relationship, and decreased fatiguability compared with controls. PAR-1 null soleus muscles also had increased type 1 and decreased type IIb/x fiber numbers compared with controls. In PAR-1 null EDL muscles, no differences were found, except for a slower rate of fatigue compared with controls.
  
  
  CONCLUSIONS
  The absence of PAR-1 results in a slower skeletal muscle contractile phenotype, likely due to an increase in type I and a decrease in type IIb/x fiber numbers. Muscle Nerve 50: 991-998, 2014.
authors.affiliation: School of Anatomy, Physiology and Human Biology, M311, The University of Western Australia, Crawley, WA, 6009, Australia.
authors.forename: Paran K
authors.initials: PK
authors.lastname: Sitparan
authors.forename: Charles N
authors.initials: CN
authors.lastname: Pagel
authors.forename: Gavin J
authors.initials: GJ
authors.lastname: Pinniger
authors.forename: H J
authors.initials: HJ
authors.lastname: Yoo
authors.forename: Eleanor J
authors.initials: EJ
authors.lastname: Mackie
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Bakker
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D005260:Female; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D010641:Phenotype; D044463:Receptor, PAR-1 / Q000172:deficiency* / Q000235:genetics / Q000502:physiology
chemical_list: D044463:Receptor, PAR-1
keywords: Ca2+; calcium; contraction; damage; development; eccentric; exercise; fatigue; force; inflammation; injury; motor; mouse; myoblast; myotube; necrosis; nerve; neuron; primary fibers; proteinase; regeneration; secondary fibers; synapse; thrombin; trypsin