Elsevier

Neuroscience

Volume 6, Issue 12, December 1981, Pages 2423-2430
Neuroscience

Ionic currents in the somatic membrane of rat dorsal root ganglion neurons—I. Sodium currents

https://doi.org/10.1016/0306-4522(81)90088-9Get rights and content

Abstract

Measurements of sodium transmembrane ionic currents evoked by depolarizing shifts in membrane potential have been performed on isolated dorsal root ganglion neurons of 5–10-day-old rats. Potassium currents were eliminated by dialysing the neurons with potassium-free solutions. In 10–15% of investigated neurons a tetrodotoxin-resistant component has been revealed in the sodium inward current which differs in its potential-dependent and kinetic characteristics from the main tetrodotoxinsensitive one. The activation kinetics of the tetrodotoxin-sensitive sodium current could be described by the Hodgkin-Huxley model using the cubic power of the m-variable, whereas the activation kinetics of the tetrodotoxin-resistant one can be described using only the square power of m. The time constants of activation and inactivation of the tetrodotoxin-resistant current were about ten times longer than those of the tetrodotoxin-sensitive current. The tetrodotoxin-resistant current was highly sensitive to all extracellular agents which are known as effective blockers of calcium channels (Co2+, Mn2+, Cd2+, D-600 and its derivatives). At the same time, the selectivity of the corresponding channels did not differ significantly from the selectivity of the tetrodotoxin-sensitive sodium channels. The sequence of relative permeabilities for univalent cations wasPNa: PLi: Phydrazinium:PNH4:Phydroxylammonium:PK = 1.0:0.79:0.43:0.33:0.25:0.18 for the tetrodotoxin-sensitive channels and 1.0:0.98:0.47:0.42:0.26:0.26 for the tetrodotoxin-resistant ones.

Thus, the tetrodotoxin-resistant sodium channels combine some features of sodium (the selective filter) and calcium (gating mechanism and binding properties) channels.

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