Distinct effects on Ca2+ handling caused by malignant hyperthermia and central core disease mutations in RyR1.
Malignant hyperthermia (MH) and central core disease (CCD) are disorders of skeletal muscle Ca2+ homeostasis that are linked to mutations in the type 1 ryanodine receptor (RyR1). Certain RyR1 mutations result in an MH-selective phenotype (MH-only), whereas others result in a mixed phenotype (MH + CCD). We characterized effects on Ca2+ handling and excitation-contraction (EC) coupling of MH-only and MH + CCD mutations in RyR1 after expression in skeletal myotubes derived from RyR1-null (dyspedic) mice. Compared to wild-type RyR1-expressing myotubes, MH + CCD- and MH-only-expressing myotubes exhibited voltage-gated Ca2+ release (VGCR) that activated at more negative potentials and displayed a significantly higher incidence of spontaneous Ca2+ oscillations. However, maximal VGCR was reduced only for MH + CCD mutants (Y4795C, R2435L, and R2163H) in which spontaneous Ca2+ oscillations occurred with significantly longer duration (Y4795C and R2435L) or higher frequency (R2163H). Notably, myotubes expressing these MH + CCD mutations in RyR1 exhibited both increased [Ca2+]i and reduced sarcoplasmic reticulum (SR) Ca2+ content. We conclude that MH-only mutations modestly increase basal release-channel activity in a manner insufficient to alter net SR Ca2+ content ("compensated leak"), whereas the mixed MH + CCD phenotype arises from mutations that enhance basal activity to a level sufficient to promote SR Ca2+ depletion, elevate [Ca2+]i, and reduce maximal VGCR ("decompensated leak").
Dirksen
Robert T
RT
Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York, USA.
Avila
Guillermo
G
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002478:Cells, Cultured; D005334:Fever / Q000378:metabolism*; D006801:Humans; D015640:Ion Channel Gating; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D020512:Myopathy, Central Core / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013329:Structure-Activity Relationship
D011994:Recombinant Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium