Excitation--contraction uncoupling by a human central core disease mutation in the ryanodine receptor.
Central core disease (CCD) is a human congenital myopathy characterized by fetal hypotonia and proximal muscle weakness that is linked to mutations in the gene encoding the type-1 ryanodine receptor (RyR1). CCD is thought to arise from Ca(2+)-induced damage stemming from mutant RyR1 proteins forming "leaky" sarcoplasmic reticulum (SR) Ca(2+) release channels. A novel mutation in the C-terminal region of RyR1 (I4898T) accounts for an unusually severe and highly penetrant form of CCD in humans [Lynch, P. J., Tong, J., Lehane, M., Mallet, A., Giblin, L., Heffron, J. J., Vaughan, P., Zafra, G., MacLennan, D. H. & McCarthy, T. V. (1999) Proc. Natl. Acad. Sci. USA 96, 4164--4169]. We expressed in skeletal myotubes derived from RyR1-knockout (dyspedic) mice the analogous mutation engineered into a rabbit RyR1 cDNA (I4897T). Here we show that homozygous expression of I4897T in dyspedic myotubes results in a complete uncoupling of sarcolemmal excitation from voltage-gated SR Ca(2+) release without significantly altering resting cytosolic Ca(2+) levels, SR Ca(2+) content, or RyR1-mediated enhancement of dihydropyridine receptor (DHPR) channel activity. Coexpression of both I4897T and wild-type RyR1 resulted in a 60% reduction in voltage-gated SR Ca(2+) release, again without altering resting cytosolic Ca(2+) levels, SR Ca(2+) content, or DHPR channel activity. These findings indicate that muscle weakness suffered by individuals possessing the I4898T mutation involves a functional uncoupling of sarcolemmal excitation from SR Ca(2+) release, rather than the expression of overactive or leaky SR Ca(2+) release channels.
Department of Pharmacology and Physiology, University of Rochester, 601 Elmwood Avenue, Rochester, NY 14642, USA.
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Avila
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O'Brien
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Dirksen
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004594:Electrophysiology; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology*; D009154:Mutation; D020512:Myopathy, Central Core / Q000235:genetics*; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics* / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism / Q000502:physiology; D014162:Transfection
D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium