Pyramidal cells of rodent presubiculum express a tetrodotoxin-insensitive Na+ current

J Physiol. 2009 Sep 1;587(Pt 17):4249-64. doi: 10.1113/jphysiol.2009.175349. Epub 2009 Jul 13.


Presubicular neurons are activated physiologically by a specific preferred head direction. Here we show that firing in these neurones is characterized by action potentials with a large overshoot and a reduced firing frequency adaptation during repetitive firing. We found that a component of the sodium current of presubicular cells was not abolished by tetrodotoxin (TTX, 10 mum) and was activated at more depolarized voltages than TTX-sensitive currents. This inward current was completely abolished by the removal of external sodium, suggesting that sodium is the charge carrier of this TTX-insensitive (TTX-I) current. The channels responsible for the TTX-I sodium current seemed to be expressed at sites distant from the soma, giving rise to a voltage-dependent delay in current activation. The voltage required for half-maximal activation was 21 mV, and 36 mV for inactivation, which is similar to that reported for Na(V)1.8 sodium channels. However, the kinetics were considerably slower, with a time constant of current decay of 1.4 s. The current was not abolished in pyramidal cells from animals lacking either the Na(V)1.8 or the Na(V)1.9 subunit. This, possibly novel, TTX-I sodium current could contribute to the coding functions of presubicular neurons, specifically the maintained firing associated with signalling of a stable head position.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cells, Cultured
  • Dose-Response Relationship, Drug
  • Ion Channel Gating / drug effects
  • Ion Channel Gating / physiology*
  • Parahippocampal Gyrus / drug effects
  • Parahippocampal Gyrus / physiology*
  • Pyramidal Cells / drug effects
  • Pyramidal Cells / physiology*
  • Rats
  • Rats, Sprague-Dawley
  • Sodium / metabolism*
  • Sodium Channel Blockers / administration & dosage
  • Sodium Channels / drug effects
  • Sodium Channels / physiology*
  • Tetrodotoxin / administration & dosage*


  • Sodium Channel Blockers
  • Sodium Channels
  • Tetrodotoxin
  • Sodium