title: Myoplasmic calcium regulation in myotubes from horses with recurrent exertional rhabdomyolysis.
abstract: OBJECTIVE
  To determine whether alterations in myoplasmic calcium regulation can be identified in muscle cell cultures (myotubes) and intact muscle fiber bundles derived from Thoroughbreds affected with recurrent exertional rhabdomyolysis (RER).
  
  
  METHODS
  6 related Thoroughbreds with RER and 8 clinically normal (control) Thoroughbred or crossbred horses.
  
  
  METHODS
  Myotube cell cultures were grown from satellite cells obtained from muscle biopsy specimens of RER-affected and control horses. Fura-2 fluorescence was used to measure resting myoplasmic calcium concentration as well as caffeine- and 4-chloro-m-cresol (4-CMC)-induced increases in myoplasmic calcium. In addition, intact intercostal muscle fiber bundles were prepared from both types of horses, and their sensitivities to caffeine- and 4-CMC-induced contractures were determined.
  
  
  RESULTS
  Myotubes of RER-affected and control horses had identical resting myoplasmic calcium concentrations. Myotubes from RER-affected horses had significantly higher myoplasmic calcium concentrations than myotubes from control horses following the addition of > or = 2mM caffeine; however, there was no difference in their response to 4-CMC (> or = 1 mM). Caffeine contracture thresholds for RER and control intact muscle cell bundles (2 vs 10mM, respectively) were significantly different, but 4-CMC contracture thresholds of muscle bundles from RER-affected and control horses (500 microM) did not differ.
  
  
  CONCLUSIONS
  An increase in caffeine sensitivity of muscle cells derived from a family of related RER-affected horses was detected in vitro by use of cell culture with calcium imaging and by use of fiber bundle contractility techniques. An alteration in muscle cell calcium regulation is a primary factor in the cause of this heritable myopathy.
authors.affiliation: Department of Clinical and Population Sciences, University of Minnesota, St Paul, MN 55108, USA.
authors.forename: Linnea R
authors.initials: LR
authors.lastname: Lentz
authors.forename: Stephanie J
authors.initials: SJ
authors.lastname: Valberg
authors.forename: Lee V
authors.initials: LV
authors.lastname: Herold
authors.forename: Gary W
authors.initials: GW
authors.lastname: Onan
authors.forename: James R
authors.initials: JR
authors.lastname: Mickelson
authors.forename: Esther M
authors.initials: EM
authors.lastname: Gallant
mesh_terms: D000818:Animals; D001706:Biopsy / Q000662:veterinary; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D003408:Cresols / Q000494:pharmacology; D005260:Female; D005456:Fluorescent Dyes / Q000737:chemistry; D016257:Fura-2 / Q000737:chemistry; D006734:Horse Diseases / Q000378:metabolism* / Q000503:physiopathology; D006736:Horses; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D008856:Microscopy, Fluorescence / Q000662:veterinary; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D005082:Physical Exertion; D012206:Rhabdomyolysis / Q000235:genetics / Q000503:physiopathology / Q000662:veterinary*
chemical_list: D000697:Central Nervous System Stimulants; D003408:Cresols; D005456:Fluorescent Dyes; D002110:Caffeine; D002118:Calcium; D016257:Fura-2