Postnatal development of A-type and Kv1- and Kv2-mediated potassium channel currents in neocortical pyramidal neurons

Abstract

Guan D, Horton LR, Armstrong WE, Foehring RC. Postnatal development of A-type and Kv1-and Kv2-mediated potassium channel currents in neocortical pyramidal neurons. J Neurophysiol 105: 2976-2988, 2011. First published March 30, 2011 doi:10.1152/jn.00758.2010.-Potassium channels regulate numerous aspects of neuronal excitability, and several voltage-gated K ϩ channel subunits have been identified in pyramidal neurons of rat neocortex. Previous studies have either considered the development of outward current as a whole or divided currents into transient, A-type and persistent, delayed rectifier components but did not differentiate between current components defined by ␣-subunit type. To facilitate comparisons of studies reporting K ϩ currents from animals of different ages and to understand the functional roles of specific current components, we characterized the postnatal development of identified Kv channel-mediated currents in pyramidal neurons from layers II/III from rat somatosensory cortex. Both the persistent/slowly inactivating and transient components of the total K ϩ current increased in density with postnatal age. We used specific pharmacological agents to test the relative contributions of putative Kv1-and Kv2-mediated currents (100 nM ␣-dendrotoxin and 600 nM stromatoxin, respectively). A combination of voltage protocol, pharmacology, and curve fitting was used to isolate the rapidly inactivating A-type current. We found that the density of all identified current components increased with postnatal age, approaching a plateau at 3-5 wk. We found no significant changes in the relative proportions or kinetics of any component between postnatal weeks 1 and 5, except that the activation time constant for A-type current was longer at 1 wk. The putative Kv2-mediated component was the largest at all ages. Immunocytochemistry indicated that protein expression for Kv4.2, Kv4.3, Kv1.4, and Kv2.1 increased between 1 wk and 4 -5 wk of age. Kv channel; somatosensory cortex; voltage clamp; A current; delayed rectifier AT BIRTH, the rodent somatosensory system is immature, and somatosensory cortex undergoes dramatic changes over the first postnatal month. Neocortical pyramidal cells are generated prenatally in an "inside-out" laminar pattern (Caviness 1982; Caviness et al.

Kv2 Channel Regulation of Action Potential Repolarization and Firing Patterns in Superior Cervical Ganglion Neurons and Hippocampal CA1 Pyramidal Neurons

“…We found that some of the GxTX-resistant current could be blocked by 1 mM TEA, but this block was not selective because 1 mM TEA also clearly partially inhibited the slowly-activating slowly-deactivating GxTX-sensitive component of current. This is consistent with a previous demonstration that the Kv2-mediated current in cortical pyramidal neurons is sensitive to low millimolar concentrations of TEA (Guan et al, 2007). Although the current remaining in GxTX-1E appeared heterogenous and varied in its kinetics from cell to cell, the GxTX-sensitive component was highly consistent in its voltage dependence and kinetics from cell to cell.…”

“…The voltage dependence of the collected data was described fairly well by a simple Boltzmann curve constructed from the averaged midpoints and slope factors of the individual cells, with a midpoint of Ϫ11.2 Ϯ 1.3 mV and slope factor of 10.4 Ϯ 0.5 mV (n ϭ 20). This voltage dependence is generally similar to that of Kv2 current in neocortical pyramidal neurons defined by stromatoxin block (midpoint Ϫ3 mV, slope factor 10.5 mV; Guan et al, 2007) and a component of current in globus pallidus neurons with slow deactivation proposed to be Kv2 mediated (midpoint Ϫ18 mV, slope factor 7 mV; Baranauskas et al, 1999). Figure 8 shows the kinetics of the GxTX-sensitive current in CA1 pyramidal neurons.…”

“…We believe the GxTX-resistant current likely contains multiple components, because the speed and degree of inactivation varied considerably from cell to cell. Based on previous analysis of potassium currents in hippocampal and cortical pyramidal neurons, the GxTXresistant current includes components from Kv4 and Kv1 family subunits (Kim et al, 2005;Chen et al, 2006;Guan et al, 2007aGuan et al, , 2007bGuan et al, , 2011Carrasquillo et al, 2012;Kim and Hoffman, 2012). We found that some of the GxTX-resistant current could be blocked by 1 mM TEA, but this block was not selective because 1 mM TEA also clearly partially inhibited the slowly-activating slowly-deactivating GxTX-sensitive component of current.…”

“…Among the most widely expressed potassium channels in neurons of the mammalian brain are Kv2 family channels (Trimmer, 1991;Hwang et al, 1993;Scannevin et al, 1996;Du et al, 1998Du et al, , 2000Guan et al, 2007). Kv2 channels produce "delayed-rectifier" currents that activate more slowly than many other voltage-dependent potassium channels, including most Kv1, Kv3, and Kv4 family channels.…”

“…Hanatoxin and stromatoxin are both effective inhibitors of Kv2 channels, but also potently inhibit Kv4-mediated A-type (I A ) current (Swartz andMacKinnon, 1995, 1997;Escoubas et al, 2002). Stromatoxin can be used effectively to characterize Kv2 channels in voltage-clamp experiments, where effects on I A can be minimized using appropriate voltage protocols (Guan et al, 2007). However, the lack of selectivity precludes its use in current-clamp experiments studying excitability, where such strategies are impossible.…”