Divergent Activity Profiles of Type 1 Ryanodine Receptor Channels Carrying Malignant Hyperthermia and Central Core Disease Mutations in the Amino-Terminal Region

PLoS One. 2015 Jun 26;10(6):e0130606. doi: 10.1371/journal.pone.0130606. eCollection 2015.

Abstract

The type 1 ryanodine receptor (RyR1) is a Ca2+ release channel in the sarcoplasmic reticulum of skeletal muscle and is mutated in several diseases, including malignant hyperthermia (MH) and central core disease (CCD). Most MH and CCD mutations cause accelerated Ca2+ release, resulting in abnormal Ca2+ homeostasis in skeletal muscle. However, how specific mutations affect the channel to produce different phenotypes is not well understood. In this study, we have investigated 11 mutations at 7 different positions in the amino (N)-terminal region of RyR1 (9 MH and 2 MH/CCD mutations) using a heterologous expression system in HEK293 cells. In live-cell Ca2+ imaging at room temperature (~25 °C), cells expressing mutant channels exhibited alterations in Ca2+ homeostasis, i.e., an enhanced sensitivity to caffeine, a depletion of Ca2+ in the ER and an increase in resting cytoplasmic Ca2+. RyR1 channel activity was quantitatively evaluated by [3H]ryanodine binding and three parameters (sensitivity to activating Ca2+, sensitivity to inactivating Ca2+ and attainable maximum activity, i.e., gain) were obtained by fitting analysis. The mutations increased the gain and the sensitivity to activating Ca2+ in a site-specific manner. The gain was consistently higher in both MH and MH/CCD mutations. Sensitivity to activating Ca2+ was markedly enhanced in MH/CCD mutations. The channel activity estimated from the three parameters provides a reasonable explanation to the pathological phenotype assessed by Ca2+ homeostasis. These properties were also observed at higher temperatures (~37 °C). Our data suggest that divergent activity profiles may cause varied disease phenotypes by specific mutations. This approach should be useful for diagnosis and treatment of diseases with mutations in RyR1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calcium / metabolism*
  • Cell Line
  • Cytoplasm / metabolism*
  • Humans
  • Malignant Hyperthermia / metabolism*
  • Mutation
  • Myopathy, Central Core / metabolism*
  • Ryanodine Receptor Calcium Release Channel / genetics
  • Ryanodine Receptor Calcium Release Channel / metabolism*

Substances

  • Ryanodine Receptor Calcium Release Channel
  • Calcium

Grant support

This work was supported in part by Grants-in-Aid for Scientific Research (24590330 to TM, 24590331 and 25136718 to NK, and 25460303 to TY) by Japan Society for the Promotion of Science (JSPS), a Grant-in-Aid for Scientific Research (25221304 to MI) by The Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Vehicle Racing Commemorative Foundation (http://www.vecof.or.jp/) (to NK), the Institute of Seizon & Life Sciences (http://seizon.umin.jp/) (to NK), and MEXT-supported Program for the Strategic Research Foundation at Private Universities. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.