title: Ca2+ release in muscle fibers expressing R4892W and G4896V type 1 ryanodine receptor disease mutants.
abstract: The large and rapidly increasing number of potentially pathological mutants in the type 1 ryanodine receptor (RyR1) prompts the need to characterize their effects on voltage-activated sarcoplasmic reticulum (SR) Ca(2+) release in skeletal muscle. Here we evaluated the function of the R4892W and G4896V RyR1 mutants, both associated with central core disease (CCD) in humans, in myotubes and in adult muscle fibers. For both mutants expressed in RyR1-null (dyspedic) myotubes, voltage-gated Ca(2+) release was absent following homotypic expression and only partially restored following heterotypic expression with wild-type (WT) RyR1. In muscle fibers from adult WT mice, both mutants were expressed in restricted regions of the fibers with a pattern consistent with triadic localization. Voltage-clamp-activated confocal Ca(2+) signals showed that fiber regions endowed with G4896V-RyR1s exhibited an ∼30% reduction in the peak rate of SR Ca(2+) release, with no significant change in SR Ca(2+) content. Immunostaining revealed no associated change in the expression of either α1S subunit (Cav1.1) of the dihydropyridine receptor (DHPR) or type 1 sarco(endo)plasmic reticulum Ca(2+) ATPase (SERCA1), indicating that the reduced Ca(2+) release resulted from defective RyR1 function. Interestingly, in spite of robust localized junctional expression, the R4892W mutant did not affect SR Ca(2+) release in adult muscle fibers, consistent with a low functional penetrance of this particular CCD-associated mutant.
authors: Centre de Génétique et de Physiologie Moléculaire et Cellulaire, CNRS UMR 5534-Université Lyon 1, Villeurbanne, France.
authors: Romain
authors: R
authors: Lefebvre
authors: Claude
authors: C
authors: Legrand
authors: Linda
authors: L
authors: Groom
authors: Robert T
authors: RT
authors: Dirksen
authors: Vincent
authors: V
authors: Jacquemond
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism; D020013:Calcium Signaling; D015870:Gene Expression; D005816:Genetic Complementation Test; D006801:Humans; D015640:Ion Channel Gating; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000473:pathology; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D009154:Mutation; D020512:Myopathy, Central Core / Q000378:metabolism / Q000503:physiopathology; D018408:Patch-Clamp Techniques; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics* / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism* / Q000473:pathology; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism
chemical_list: C506944:Atp2a1 protein, mouse; C529218:CACNA1S protein, mouse; D020746:Calcium Channels, L-Type; D019837:Ryanodine Receptor Calcium Release Channel; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium