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Electrophysiological properties of sodium current subtypes in small cells from adult rat dorsal root ganglia
Author(s) -
Rush A. M.,
Bräu M. E.,
Elliott A. A.,
Elliott J. R.
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.771bg.x
Subject(s) - electrophysiology , dorsum , sodium channel , neuroscience , anatomy , biology , sodium , chemistry , biophysics , organic chemistry
1 Whole‐cell and single‐channel Na + currents were recorded from small (ca. 20 μ m diameter) cells isolated from adult rat dorsal root ganglia (DRG). Currents were classified by their sensitivity to 0.3 μ m tetrodotoxin (TTX), electrophysiological properties and single‐channel amplitude. Cells were classified according to the types of current recorded from them. 2 Type A cells expressed essentially pure TTX‐sensitive (TTX‐S) currents. Availability experiments with prepulse durations between 50 ms and 1 s gave a half‐available voltage ( V h ) of around ‐65 mV but the availability curves often had a complex shape, consistent with multiple inactivation processes. Measured inactivation time constants ranged from less than 1 ms to over 100 s, depending on the protocol used. 3 Cell types B and C each had, in addition to TTX‐S currents, substantial and different TTX‐resistant (TTX‐R) currents that we have designated TTX‐R1 and TTX‐R2, respectively. TTX‐R1 currents had a 1 s V h of ‐29 mV, showed little 1 Hz use dependence at ‐67 mV and recovered from the inactivation induced by a 60 ms depolarizing pulse with time constants of 1.6 ms (91 %) and 908 ms. They also exhibited slow inactivation processes with component time constants around 10 and 100 s. TTX‐R2 currents activated and inactivated at more negative potentials (1 s V h = ‐46 mV), showed substantial 1 Hz use dependence and had inactivation (60 ms pulse) recovery time constants at ‐67 mV of 3.3 ms (58 %) and 902 ms. 4 Type D cells had little or no current in 0.3 μ m TTX at a holding potential of ‐67 mV. Current amplitude increased on changing the holding potential to ‐107 mV. Type D cell currents had more hyperpolarized availability and I‐V curves than even TTX‐R2 currents and suggest the existence of TTX‐R3 channels. 5 In outside‐out patches with 250 mM external NaCl, the single‐channel conductance (γ) of TTX‐S channels was 19.5 pS and the potential for half‐maximal activation ( V a ) was ‐45 mV. One population of TTX‐R channels had a γ of 9.2 pS and a V a of ‐27 mV. A second population had a γ of 16.5 pS and a more negative V a of ‐42 mV. The latter population may underlie the type D cell current. 6 Small DRG cells express multiple Na + currents with varied time constants and voltage dependences of activation and inactivation. Nociceptive cells still fire when chronically depolarized by an increased external K + concentration. TTX‐R1 and TTX‐R2 Na + channels may support that firing, while the range of inactivation time constants described here would increase the repertoire of DRG cell burst firing behaviour generally.