Voltage-gated K+ channels in layer 5 neocortical pyramidal neurones from young rats: subtypes and gradients

Authors

  • Alon Korngreen,

    Corresponding author
    1. Abteilung Zellphysiologie, Max-Planck-Institut für Medizinische Forschung, Jahnstrasse 29, D-69120 Heidelberg, Germany
    • Corresponding author
      A. Korngreen: Abteilung Zellphysiologie, Max-Planck-Institut für Medizinische Forschung, Jahnstrasse 29, D-69120 Heidelberg, Germany. Email: alon@mpimf-heidelberg.mpg.de

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  • Bert Sakmann

    1. Abteilung Zellphysiologie, Max-Planck-Institut für Medizinische Forschung, Jahnstrasse 29, D-69120 Heidelberg, Germany
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Abstract

  • 1We investigated the types and distribution of voltage-gated K+ channels in the soma and apical dendrite of layer 5 (L5) neocortical pyramidal neurones, of young rats (postnatal days 13–15), in acute brain slices.
  • 2A slow inactivating outward K+ current and a fast inactivating outward K+ current were detected in nucleated patches. The slow K+ current was completely blocked by tetraethylammonium (TEA) with an IC50 of 5 ± 1 mm (mean ±s.e.m.) and was partially blocked by 4-aminopyridine (4-AP). The fast K+ current was blocked by 4-AP with an IC50 of 4.2 ± 0.5 mM, but was not blocked by TEA.
  • 3The activation kinetics of the slow K+ current were described by a second order Hodgkin-Huxley model. The slow K+ current displayed bi-exponential inactivation. A fourth order Hodgkin-Huxley model for activation and first order for inactivation described the kinetics of the fast K+ current.
  • 4In somatic cell-attached recordings, three classes of single K+ channels could be differentiated based on their unitary conductance and inactivation kinetics, a fast inactivating channel having a conductance of 13 ± 1 pS, a slow inactivating channel having a conductance of 9.5 ± 0.5 pS, and a very slowly inactivating channel having a conductance of 16 ± 1 pS.
  • 5The inactivation time constants of the slow and of the very slow K+ channel corresponded to the two inactivation time constants of the slow K+ current observed in nucleated patches. This suggested that two distinct K+ channels mediated the slow K+ current in nucleated patches.
  • 6The three subtypes of K+ channels that were observed in somatic recordings were present along the apical dendrite. The amplitude of ensemble K+ currents in cell-attached patches decreased along the apical dendrite as the distance from the soma increased, with a slope of −0.9 ± 0.3 pA per 100 μm.
  • 7The results suggest that the decrease of the voltage-gated K+ channel density from the soma along the apical dendrite of L5 pyramidal neurones helps to define a distal, low threshold region for the initiation of dendritic regenerative potentials.

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