Pyramidal cells of rodent presubiculum express a tetrodotoxin-insensitive Na+ current.
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.
Fricker
Desdemona
D
CRICM - CNRS UMR7225, CHU Pitié-Salpêtrière, 105 Bd de l'Hôpital, 75013 Paris, France. desdemona.fricker@upmc.fr
Dinocourt
Céline
C
Eugène
Emmanuel
E
Wood
John N
JN
Wood
John
J
Miles
Richard
R
D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D020534:Parahippocampal Gyrus / Q000187:drug effects / Q000502:physiology*; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D026941:Sodium Channel Blockers / Q000008:administration & dosage; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000008:administration & dosage*
D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013779:Tetrodotoxin; D012964:Sodium