Single Channel Properties of Heterotetrameric Mutant RyR1 Ion Channels Linked to Core Myopathies

J Biol Chem. 2008 Mar 7;283(10):6321-9. doi: 10.1074/jbc.M707353200. Epub 2008 Jan 1.

Abstract

Skeletal muscle excitation-contraction coupling involves activation of homotetrameric ryanodine receptor ion channels (RyR1s), resulting in the rapid release of Ca(2+) from the sarcoplasmic reticulum. Previous work has shown that Ca(2+) release is impaired by mutations in RyR1 linked to Central Core Disease and Multiple Minicore Disease. We studied the consequences of these mutations on RyR1 function, following their expression in human embryonic kidney 293 cells and incorporation in lipid bilayers. RyR1-G4898E, -G4898R, and -DeltaV4926/I4927 mutants in the C-terminal pore region of RyR1 and N-terminal RyR1-R110W/L486V mutant all showed negligible Ca(2+) permeation and loss of Ca(2+)-dependent channel activity but maintained reduced K(+) conductances. Co-expression of wild type and mutant RyR1s resulted in Ca(2+)-dependent channel activities that exhibited intermediate Ca(2+) selectivities compared with K(+), which suggested the presence of tetrameric RyR1 complexes composed of wild type and mutant subunits. The number of wild-type subunits to maintain a functional heterotetrameric channel differed among the four RyR1 mutants. The results indicate that homozygous RyR1 mutations associated with core myopathies abolish or greatly reduce sarcoplasmic reticulum Ca(2+) release during excitation-contraction coupling. They further suggest that in individuals, expressing wild type and mutant alleles, a substantial portion of RyR1 channels is able to release Ca(2+) from sarcoplasmic reticulum.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Substitution
  • Animals
  • Calcium / metabolism*
  • Cell Line
  • Humans
  • Muscle Contraction / genetics
  • Muscle, Skeletal / metabolism*
  • Mutation, Missense*
  • Myopathy, Central Core / genetics
  • Myopathy, Central Core / metabolism
  • Potassium / metabolism*
  • Rabbits
  • Ryanodine Receptor Calcium Release Channel / genetics
  • Ryanodine Receptor Calcium Release Channel / metabolism*
  • Sarcoplasmic Reticulum / genetics
  • Sarcoplasmic Reticulum / metabolism*

Substances

  • Ryanodine Receptor Calcium Release Channel
  • Potassium
  • Calcium