Functional specialization of the axon initial segment by isoform-specific sodium channel targeting

J Neurosci. 2003 Mar 15;23(6):2306-13. doi: 10.1523/JNEUROSCI.23-06-02306.2003.

Abstract

Voltage-dependent sodium channels cluster at high density at axon initial segments, where propagating action potentials are thought to arise, and at nodes of Ranvier. Here, we show that the sodium channel Na(v)1.6 is precisely localized at initial segments of retinal ganglion cells (RGCs), whereas a different isoform, Na(v)1.2, is found in the neighboring unmyelinated axon. During development, initial segments first expressed Na(v)1.2, and Na(v)1.6 appeared later, approximately in parallel with the onset of repetitive RGC firing. In Shiverer mice, Na(v)1.6 localization at the initial segment was unaffected, although Na(v)1.6 expression was severely disrupted in the aberrantly myelinated optic nerve. Targeting or retention of Na(v)1.6 requires molecular interactions that normally occur only at initial segments and nodes of Ranvier. Expression at nodes but not initial segments exhibits an additional requirement for intact myelination. Because of their high density at the initial segment, Na(v)1.6 channels may be crucial in determining neuronal firing properties.

Publication types

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

MeSH terms

  • Animals
  • Ankyrins / biosynthesis
  • Axons / metabolism*
  • Cell Adhesion Molecules / biosynthesis
  • Cell Differentiation / physiology
  • Fluorescent Antibody Technique
  • Immunohistochemistry
  • Mice
  • Mice, Neurologic Mutants
  • Myelin Sheath / genetics
  • Myelin Sheath / metabolism
  • Myelin Sheath / pathology
  • NAV1.2 Voltage-Gated Sodium Channel
  • Nerve Growth Factors / biosynthesis
  • Nerve Tissue Proteins / biosynthesis
  • Optic Nerve / pathology
  • Protein Isoforms / genetics
  • Protein Isoforms / metabolism*
  • Rats
  • Rats, Sprague-Dawley
  • Retina / cytology
  • Retinal Ganglion Cells / cytology
  • Retinal Ganglion Cells / metabolism
  • Sodium Channels / biosynthesis*
  • Sodium Channels / genetics

Substances

  • Ank3 protein, mouse
  • Ank3 protein, rat
  • Ankyrins
  • Cell Adhesion Molecules
  • NAV1.2 Voltage-Gated Sodium Channel
  • Nerve Growth Factors
  • Nerve Tissue Proteins
  • Nfasc protein, mouse
  • Nfasc protein, rat
  • Protein Isoforms
  • Scn2A protein, rat
  • Scn2a protein, mouse
  • Sodium Channels