title: Effects of stretch-activated channel blockers on [Ca2+]i and muscle damage in the mdx mouse.
abstract: The mdx mouse lacks dystrophin and is a model of human Duchenne muscular dystrophy. Single mdx muscle fibres were isolated and subjected to a series of stretched (eccentric) contractions while measuring intracellular calcium concentration ([Ca(2+)](i)) with fluo-3 and confocal microscopy. Following the stretched contractions there was a slow rise in resting [Ca(2+)](i) and after 30 min both the [Ca(2+)](i) during a tetanus (tetanic [Ca(2+)](i)) and the tetanic force were reduced. Two blockers of stretch-activated channels, streptomycin and the spider venom toxin GsMTx4, prevented the rise of resting [Ca(2+)](i) and partially prevented the decline of tetanic [Ca(2+)](i) and force. Reducing extracellular calcium to zero also prevented the rise in resting [Ca(2+)](i) and prevented some of the decline in tetanic [Ca(2+)](i) and force. Patch-clamping experiments identified a stretch-activated channel in both wild-type and mdx myotubes which was blocked by GsMTx4. These data suggest that blockers of stretch-activated channels can ameliorate the force reduction following stretched contractions by reducing the influx of Ca(2+) into the muscle. We therefore tested whether in intact mdx mice streptomycin, added to the drinking water, was capable of reducing muscle damage. mdx mice show a period of muscle damage from 20 to 40 days of life and fibres which regenerate from this damage display central nuclei. We measured the frequency of central nuclei in control mdx mice compared to streptomycin-treated mdx mice and showed that the incidence of central nuclei was significantly reduced by streptomycin treatment. This result suggests that blockers of stretch-activated channels may protect against muscle damage in the intact mdx mouse.
authors.affiliation: School of Medical Sciences and Institute for Biomedical Research, University of Sydney F13, NSW 2006, Australia.
authors.forename: Ella W
authors.initials: EW
authors.lastname: Yeung
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Whitehead
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Suchyna
authors.forename: Philip A
authors.initials: PA
authors.lastname: Gottlieb
authors.forename: Frederick
authors.initials: F
authors.lastname: Sachs
authors.forename: David G
authors.initials: DG
authors.lastname: Allen
mesh_terms: D000814:Aniline Compounds; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects*; D002467:Cell Nucleus / Q000187:drug effects / Q000473:pathology; D004558:Electric Stimulation; D004594:Electrophysiology; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D036341:Intercellular Signaling Peptides and Proteins; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D018101:Mice, Inbred mdx; D018613:Microscopy, Confocal; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000473:pathology / Q000502:physiology; D009470:Muscle Spindles / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000473:pathology; D009137:Muscular Dystrophy, Animal / Q000473:pathology* / Q000517:prevention & control; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D013111:Spider Venoms / Q000494:pharmacology; D013307:Streptomycin / Q000494:pharmacology; D014966:Xanthenes
chemical_list: D000814:Aniline Compounds; D005456:Fluorescent Dyes; D036341:Intercellular Signaling Peptides and Proteins; C411249:MTx4 protein, Grammostola spatulata; D010455:Peptides; D011500:Protein Synthesis Inhibitors; D013111:Spider Venoms; D014966:Xanthenes; C059715:Fluo-3; D013307:Streptomycin