title: Muscle weakness in Ryr1I4895T/WT knock-in mice as a result of reduced ryanodine receptor Ca2+ ion permeation and release from the sarcoplasmic reticulum.
abstract: The type 1 isoform of the ryanodine receptor (RYR1) is the Ca(2+) release channel of the sarcoplasmic reticulum (SR) that is activated during skeletal muscle excitation-contraction (EC) coupling. Mutations in the RYR1 gene cause several rare inherited skeletal muscle disorders, including malignant hyperthermia and central core disease (CCD). The human RYR1(I4898T) mutation is one of the most common CCD mutations. To elucidate the mechanism by which RYR1 function is altered by this mutation, we characterized in vivo muscle strength, EC coupling, SR Ca(2+) content, and RYR1 Ca(2+) release channel function using adult heterozygous Ryr1(I4895T/+) knock-in mice (IT/+). Compared with age-matched wild-type (WT) mice, IT/+ mice exhibited significantly reduced upper body and grip strength. In spite of normal total SR Ca(2+) content, both electrically evoked and 4-chloro-m-cresol-induced Ca(2+) release were significantly reduced and slowed in single intact flexor digitorum brevis fibers isolated from 4-6-mo-old IT/+ mice. The sensitivity of the SR Ca(2+) release mechanism to activation was not enhanced in fibers of IT/+ mice. Single-channel measurements of purified recombinant channels incorporated in planar lipid bilayers revealed that Ca(2+) permeation was abolished for homotetrameric IT channels and significantly reduced for heterotetrameric WT:IT channels. Collectively, these findings indicate that in vivo muscle weakness observed in IT/+ knock-in mice arises from a reduction in the magnitude and rate of RYR1 Ca(2+) release during EC coupling that results from the mutation producing a dominant-negative suppression of RYR1 channel Ca(2+) ion permeation.
authors.affiliation: Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14642, USA.
authors.forename: Ryan E
authors.initials: RE
authors.lastname: Loy
authors.forename: Murat
authors.initials: M
authors.lastname: Orynbayev
authors.forename: Le
authors.initials: L
authors.lastname: Xu
authors.forename: Zoita
authors.initials: Z
authors.lastname: Andronache
authors.forename: Simona
authors.initials: S
authors.lastname: Apostol
authors.forename: Elena
authors.initials: E
authors.lastname: Zvaritch
authors.forename: David H
authors.initials: DH
authors.lastname: MacLennan
authors.forename: Gerhard
authors.initials: G
authors.lastname: Meissner
authors.forename: Werner
authors.initials: W
authors.lastname: Melzer
authors.forename: Robert T
authors.initials: RT
authors.lastname: Dirksen
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000235:genetics; D003408:Cresols / Q000378:metabolism; D055879:Gene Knock-In Techniques; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009119:Muscle Contraction / Q000235:genetics / Q000502:physiology; D053580:Muscle Strength / Q000235:genetics / Q000502:physiology; D018908:Muscle Weakness / Q000235:genetics* / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism / Q000503:physiopathology; D009154:Mutation; D019837:Ryanodine Receptor Calcium Release Channel / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*
chemical_list: D015220:Calcium Channels; D003408:Cresols; D019837:Ryanodine Receptor Calcium Release Channel; C032538:4-cresol; D002118:Calcium