Differential Expression of TASK Channels between Horizontal Interneurons and Pyramidal Cells of Rat Hippocampus

Abstract

Among the electrophysiological properties differentiating stratum oriens horizontal interneurons from pyramidal neurons of the CA1 hippocampal subfield are the more depolarized resting potential and the higher input resistance; additionally, these interneurons are also less sensitive to ischemic damage than pyramidal cells. A differential expression of pH-sensitive leakage potassium channels (TASK) could contribute to all of these differences. To test this hypothesis, we studied the expression and properties of TASK channels in the two cell types.Electrophysiological recordings from acute slices showed that barium-and bupivacaine-sensitive TASK currents were detectable in pyramidal cells but not in interneurons and that extracellular acidification caused a much stronger depolarization in pyramidal cells than in interneurons. This pyramidal cell depolarization was paralleled by an increase of the input resistance, suggesting the blockade of a background conductance.Single-cell reverse transcription-PCR experiments showed that the expression profile of TASK channels differ between the two cell types and suggested that these channels mediate an important share of the leakage current of pyramidal cells.We suggest that the different expression of TASK channels in these cell types contribute to their electrophysiological differences and may result in cell-specific sensitivity to extracellular acidification in conditions such as epilepsy and ischemia.

TASK-Like Conductances Are Present within Hippocampal CA1 Stratum Oriens Interneuron Subpopulations

“…Attempts to determine the TASK-3 content of other neurochemically defined populations of interneurons was equivocal and suggests that TASK-3 is largely expressed in parvalbumincontaining, and a subpopulation of somatostatin-containing interneurons. Importantly, these data indicate that TASK-3 protein is expressed in a greater number of CA1 interneurons than suggested previously (Taverna et al 2005). …”

“…TASK channel expression in SO interneurons has been previously investigated by Taverna et al (2005), who concluded that TASK-like currents are not consistently detectable in horizontal CA1 SO interneurons, and only ϳ15% of CA1 SO interneurons express TASK-3 mRNA. However, in the present study, ϳ50% of morphologically identified horizontal interneurons displayed a TASK-like current.…”

“…However, in a separate study, single cell reverse transcription (RT)-PCR suggested that only ϳ15% of CA1 SO interneurons with horizontally oriented dendrites contain TASK mRNA (Taverna et al, 2005). Furthermore, SO interneurons displayed "leakage" currents with weak acid sensitivity, consistent with expression of a TASK-like current (Taverna et al, 2005). Because CA1 SO interneurons are a heterogeneous group (Somogyi and Klausberger, 2005), the possibility exists that TASK channels are expressed in other subpopulations, accounting for the disparity between in situ hybridization and single cell RT-PCR data.…”

“…High levels of TASK-3 mRNA and lower levels of TASK-1 mRNA were observed in presumed stratum oriens (SO) inhibitory interneurons (Talley et al, 2001). However, in a separate study, single cell reverse transcription (RT)-PCR suggested that only ϳ15% of CA1 SO interneurons with horizontally oriented dendrites contain TASK mRNA (Taverna et al, 2005). Furthermore, SO interneurons displayed "leakage" currents with weak acid sensitivity, consistent with expression of a TASK-like current (Taverna et al, 2005).…”

Postnatal Differentiation of Basket Cells from Slow to Fast Signaling Devices

“…The developmental reduction in R m could be explained by increases in densities of leak channels (e.g., two-pore domain K ϩ channels) (Taverna et al, 2005;Torborg et al, 2006). Changes in morphology and membrane properties jointly redefine somatodendritic integration of EPSPs in BCs.…”