Premium
Voltage‐gated K + channels in layer 5 neocortical pyramidal neurones from young rats: subtypes and gradients
Author(s) -
Korngreen Alon,
Sakmann Bert
Publication year - 2000
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.1469-7793.2000.00621.x
Subject(s) - tetraethylammonium , conductance , chemistry , biophysics , kinetics , 4 aminopyridine , time constant , potassium channel , reversal potential , current (fluid) , pyramidal cell , patch clamp , potassium , neuroscience , biochemistry , hippocampal formation , biology , physics , receptor , organic chemistry , engineering , quantum mechanics , electrical engineering , condensed matter physics , thermodynamics
1 We 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. 2 A 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 IC 50 of 5 ± 1 m m (mean ± s.e.m. ) and was partially blocked by 4‐aminopyridine (4‐AP). The fast K + current was blocked by 4‐AP with an IC 50 of 4.2 ± 0.5 mM, but was not blocked by TEA. 3 The 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. 4 In 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. 5 The 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. 6 The 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. 7 The 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.