Gene Dose Influences Cellular and Calcium Channel Dysregulation in Heterozygous and Homozygous T4826I-RYR1 Malignant Hyperthermia-susceptible Muscle

Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, California 95616, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 12/2011; 287(4):2863-76. DOI: 10.1074/jbc.M111.307926
Source: PubMed


Malignant hyperthermia susceptibility (MHS) is primarily conferred by mutations within ryanodine receptor type 1 (RYR1). Here
we address how the MHS mutation T4826I within the S4-S5 linker influences excitation-contraction coupling and resting myoplasmic
Ca2+ concentration ([Ca2+]rest) in flexor digitorum brevis (FDB) and vastus lateralis prepared from heterozygous (Het) and homozygous (Hom) T4826I-RYR1
knock-in mice (Yuen, B. T., Boncompagni, S., Feng, W., Yang, T., Lopez, J. R., Matthaei, K. I., Goth, S. R., Protasi, F.,
Franzini-Armstrong, C., Allen, P. D., and Pessah, I. N. (2011) FASEB J. doi:22131268). FDB responses to electrical stimuli and acute halothane (0.1%, v/v) exposure showed a rank order of Hom ≫
Het ≫ WT. Release of Ca2+ from the sarcoplasmic reticulum and Ca2+ entry contributed to halothane-triggered increases in [Ca2+]rest in Hom FDBs and elicited pronounced Ca2+ oscillations in ∼30% of FDBs tested. Genotype contributed significantly elevated [Ca2+]rest (Hom > Het > WT) measured in vivo using ion-selective microelectrodes. Het and Hom oxygen consumption rates measured in intact myotubes using the Seahorse
Bioscience (Billerica, MA) flux analyzer and mitochondrial content measured with MitoTracker were lower than WT, whereas total
cellular calpain activity was higher than WT. Muscle membranes did not differ in RYR1 expression nor in Ser2844 phosphorylation among the genotypes. Single channel analysis showed highly divergent gating behavior with Hom and WT favoring
open and closed states, respectively, whereas Het exhibited heterogeneous gating behaviors. [3H]Ryanodine binding analysis revealed a gene dose influence on binding density and regulation by Ca2+, Mg2+, and temperature. Pronounced abnormalities inherent in T4826I-RYR1 channels confer MHS and promote basal disturbances of
excitation-contraction coupling, [Ca2+]rest, and oxygen consumption rates. Considering that both Het and Hom T4826I-RYR1 mice are viable, the remarkable isolated single
channel dysfunction mediated through this mutation in S4-S5 cytoplasmic linker must be highly regulated in vivo.

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Available from: Jose Rafael Lopez, Dec 29, 2015
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    • "), and sudden death (Laitinen et al. 2004). Recent studies demonstrate that specific RYR mutations con­ fer sex– and gene–dose­dependent susceptibil­ ity to pharmacological (halogenated anesthetic) and environmental (heat) stressors that trigger malignant hyperthermia and muscle damage in otherwise asymptomatic individuals (Barrientos et al. 2012; Yuen et al. 2012). Importantly, PCB­95 is significantly more potent and effica­ cious in disrupting cation regulation of mutant R615C­RYR1 compared with wild type RyR1 (Ta and Pessah 2007). "
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