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Single-channel analysis of two types of Na+currents in rat dorsal root ganglia

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  • Neurophysiology, Musele and Sensory Organs
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Abstract

The properties of voltage-gated Na+ channels were studied in neurones isolated from rat dorsal root ganglia using the outside-out configuration of the patch-clamp technique. Two types of single-channel currents were identified from the difference in unit amplitudes. Neither type was evoked in the medium in which extracellular Na+ ions were replaced by an equimolar amount of tetramethylammonium ions. The two types of single-channel currents differed in their sensitivity to tetrodotoxin (TTX). The smaller channel current was insensitive to 1 μM TTX (referred to as TTX-I), while the larger channel current was blocked by 1 nM TTX (TTX-S). The unit amplitudes measured during a step depolarization to −30 mV (1.4 mM internal and 250 mM external Na+ concentrations) were 1.16 pA for TTX-S and 0.57 pA for TTX-I, respectively. The slope conductance measured at −30 mV was 16.3 pS for TTX-S and 8.5 pS for TTX-I. TTX-S could be activated by step depolarizations positive to −60 mV, while TTX-I could be activated at potentials positive to −40 mV. When the test pulse was preceded by a depolarizing prepulse, the prepulse positive to −50 mV preferentially inactivated TTX-S with a minimal effect on TTX-I. Activation and inactivation time courses of the averaged ensemble currents computed from TTX-S showed remarkable resemblances to the time courses of the macroscopic TTX-sensitive Na+ current. Similarly, the ensemble currents of TTX-I mimicked the macroscopic TTX-insensitive Na+ current. It was concluded that the two types of Na+ channels in rat dorsal root ganglia differ not only in their sensitivity to TTX, but also in their single-channel conductances.

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Authors and Affiliations

  1. Departments of Pharmacology, Faculty of Medicine, Kyushu University, 812, Fukuoka, Japan

    Haruhiko Motomura, Sadatoshi Fujikawa & Yushi Ito

  2. Departments of Psychiatry, Faculty of Medicine, Kyushu University, 812, Fukuoka, Japan

    Nobutada Tashiro

  3. Second Department of Physiology, Faculty of Medicine, Hiroshima University, 734, Hiroshima, Japan

    Nobukuni Ogata

Authors
  1. Haruhiko Motomura
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  2. Sadatoshi Fujikawa
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  3. Nobutada Tashiro
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  4. Yushi Ito
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  5. Nobukuni Ogata
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Motomura, H., Fujikawa, S., Tashiro, N. et al. Single-channel analysis of two types of Na+currents in rat dorsal root ganglia. Pflugers Arch. 431, 221–229 (1995). https://doi.org/10.1007/BF00410194

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  • DOI: https://doi.org/10.1007/BF00410194

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