Molecular mechanisms of gating and drug block of sodium channels

Novartis Found Symp. 2002;241:206-18; discussion 218-32.

Abstract

Voltage-gated Na+ channels are composed of an alpha subunit of 260 kDa associated with beta subunits of 33-36 kDa. Alpha subunits have four homologous domains (I to IV) containing six transmembrane alpha helices (S1-S6). The S4 segments serve as voltage sensors and move outward to initiate activation. The S5 and S6 segments and the short membrane-associated loops between them form the pore. Fast inactivation is mediated by closure of an inactivation gate formed by the intracellular loop between domains III and IV. The 3-D structure of the inactivation gate has been determined bv NMR spectroscopy, revealing the conformation of the pore-blocking IFM motif. Peptide scorpion toxins that alter gating of Na+ channels bind to the extracellular ends of the IIS4 and IVS4 segments, trap them in either an activated or non-activated position, and thereby selectively alter channel activation or inactivation. Voltage sensor-trapping may be a general mechanism of toxin action on voltage-gated ion channels. Local anaesthetics block the pore of Na+ channels by binding to a receptor site in segment S6 in domains III and IV. Anticonvulsants and antiarrhythmic drugs also interact with this site. A high-affinity Na+ channel blocker has recently been developed with this site as its target. The emerging knowledge of the molecular mechanisms of Na+ channel gating and drug block may allow development of novel therapeutics for epilepsy, cardiac arrhythmia and persistent pain syndromes.

Publication types

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

MeSH terms

  • Animals
  • Brain / physiology
  • Ion Channel Gating / drug effects*
  • Ion Channel Gating / genetics
  • Models, Molecular
  • Protein Conformation
  • Protein Subunits
  • Scorpion Venoms / pharmacology
  • Sodium Channels / drug effects
  • Sodium Channels / genetics
  • Sodium Channels / physiology*

Substances

  • Protein Subunits
  • Scorpion Venoms
  • Sodium Channels