Defective fast inactivation recovery and deactivation account for sodium channel myotonia in the I1160V mutant

Biophys J. 1997 Oct;73(4):1896-903. doi: 10.1016/S0006-3495(97)78220-1.


The skeletal muscle sodium channel mutant I1160V cosegregates with a disease phenotype producing myotonic discharges (observed as muscle stiffness) that are worsened by elevated K+ levels but unaffected by cooling. The I1160V alpha-subunit was co-expressed with the beta1-subunit in Xenopus oocytes. An electrophysiological characterization was undertaken to examine the underlying biophysical characteristics imposed by this mutation. Two abnormalities were found. 1) The voltage dependence of steady-state fast inactivation was reduced in I1160V, which resulted in faster rates of closed-state fast inactivation onset and recovery in I1160V compared with wild-type channels. 2) The rates of deactivation were slower in I1160V than in wild-type channels. Using a computer-simulated model, the combination of both defects elicited myotonic runs under conditions of elevated K+, consistent with the observed phenotype of the mutant.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Base Sequence
  • Biophysical Phenomena
  • Biophysics
  • Computer Simulation
  • DNA Primers / genetics
  • Electrophysiology
  • Female
  • In Vitro Techniques
  • Kinetics
  • Membrane Potentials
  • Models, Biological
  • Mutagenesis, Site-Directed
  • Myotonia / genetics*
  • Myotonia / metabolism*
  • Oocytes / metabolism
  • Point Mutation*
  • Rats
  • Sodium Channel Blockers
  • Sodium Channels / genetics*
  • Sodium Channels / metabolism*
  • Xenopus laevis


  • DNA Primers
  • Sodium Channel Blockers
  • Sodium Channels