Low-threshold, persistent sodium current in rat large dorsal root ganglion neurons in culture.
Dorsal root ganglion neurons from adult rats (> or = 200 g) were maintained in culture for between 1 and 3 days. Membrane currents generated by large neurons (50-75 microns apparent diameter) were recorded with the whole cell patch-clamp technique. Large neurons generated transient Na+ currents and at least two types of inward current that persisted throughout 200-ms voltage-clamp steps to +20 mV. One persistent current activated close to -35 mV (high threshold), whereas in about half of the cells another persistent current began to activate negative to -70 mV (low threshold). The high-threshold persistent current was identified as a Ca2+ current, as previously described in these neurons. The low-threshold current was reversibly suppressed either by replacing external Na+ with tetramethylammonium ions or by reducing external Na+ concentration ([Na+]) and simultaneously raising external [Ca2+]. It was blocked by tetrodotoxin (TTX) with an apparent equilibrium dissociation constant in the single nanomolar range. We conclude that the low-threshold current is a TTX-sensitive, persistent Na+ current. The persistent TTX-sensitive current contributed to steady-state membrane current from at least -70 mV to 0 mV, a wider potential range than predicted by activation-inactivation gating overlap for transient Na+ current. Because of its low threshold and fast activation kinetics, the persistent Na+ current is expected to play an important role in determining membrane excitability.
Baker
M D
MD
Sobell Department of Neurophysiology, Institute of Neurology, London, United Kingdom.
Bostock
H
H
D000818:Animals; D001369:Axons / Q000187:drug effects / Q000378:metabolism; D002104:Cadmium / Q000494:pharmacology; D002478:Cells, Cultured; D004594:Electrophysiology; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology
D015222:Sodium Channels; D002104:Cadmium; D013779:Tetrodotoxin