title: Characteristics of late Na(+) current in adult rat small sensory neurons.
abstract: Na(+) currents were recorded using patch-clamp techniques from small-diameter (<25 micrometers) dorsal root ganglion neurons, cultured from adult rats (>150 g). Late Na(+) currents maintained throughout long-duration voltage-clamp steps (>/=200 ms) were of two types: a low-threshold, tetrodotoxin-sensitive (TTX-s) current that was largely blocked by 200 nM TTX, and a high-threshold, TTX-resistant (TTX-r) current. TTX-s late current was found in approximately 28% (10/36) of small-diameter neurons and was recorded only in neurons exhibiting TTX-s transient current. TTX-s transient current activation/inactivation gating overlap existed over a narrow potential range, centered between -30 and -40 mV, whereas late current operated over a wider range. The kinetics associated with de-inactivation of TTX-s late current were slow (tau approximately 37 ms at -50 mV), strongly suggesting that different subpopulations of TTX-s channel generate transient and late current. High-threshold TTX-r late current was only present in neurons generating TTX-r transient current. TTX-r late current operated over the same potential range as that for TTX-r transient current activation/inactivation gating overlap, and activation/inactivation gating overlap could be measured even after 1.5-s-duration pre-pulses. We suggest that TTX-s late sodium current results from channel openings different from those generating transient current. As in large-diameter sensory neurons, TTX-s channels generating late openings may play a key role in controlling membrane excitability. In contrast, a single population of high-threshold TTX-r channels may account for both transient and late TTX-r currents.
authors.affiliation: Sobell Department of Neurophysiology, Institute of Neurology, Queen Square, WC1N 3BG, London, UK. M.kiernan@unsw.edu.au
authors.forename: M C
authors.initials: MC
authors.lastname: Kiernan
authors.forename: M D
authors.initials: MD
authors.lastname: Baker
authors.forename: H
authors.initials: H
authors.lastname: Bostock
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D005727:Ganglia, Spinal / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D026941:Sodium Channel Blockers / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013779:Tetrodotoxin