Complex Expression and Localization of Inactivating Kv Channels in Cultured Hippocampal Astrocytes

Abstract

.Voltage-gated potassium channels are well established as critical for setting action potential frequency, membrane potential, and neurotransmitter release in neurons. However, their role in the "nonexcitable" glial cell type is yet to be fully understood. We used whole cell current kinetics, pharmacology, immunocytochemistry, and RT-PCR to characterize A-type current in hippocampal astrocyte cultures to better understand its function. Pharmacological analysis suggests that ϳ70, 10, and Ͻ5% of total A current is associated with Kv4, Kv3, and Kv1 channels, respectively. In addition, pharmacology and kinetics provide evidence for a significant contribution of KChIP accessory proteins to astrocytic A-channel composition. Localization of the Shaw Kv3.4 channel to astrocytic processes and the Shal Kv4.3 channel to soma suggest that these channels serve a specific function. Given this complex A-type channel expression pattern, we assessed the role of A currents in membrane voltage oscillations in response to current injections. Although TEAsensitive delayed-rectifying currents are involved in the extent of repolarization, 4-AP-sensitive A currents serve to increase the rate. As in neurons, this effect may enable astrocytes to respond rapidly to high-frequency synaptic events. Our results indicate that hippocampal astrocytes in vitro express multiple A-type Kv channel ␣-subunits with accessory, possibly Ca 2ϩ -sensitive, cytoplasmic subunits that appear to be specifically localized to subcellular membrane compartments. Function of these channels remains to be determined in a physiological setting. However, this study suggests that they enable astrocytes to respond rapidly with membrane voltage oscillations to high-frequency incoming signals, possibly synchronizing astrocyte function to neuronal activity.

Downregulation of Kir4.1 inward rectifying potassium channel subunits by RNAi impairs potassium transfer and glutamate uptake by cultured cortical astrocytes

“…3). This is compatible with the presence of 2P-domain K 1 channels (for review see Goldstein et al, 2001) or Kv channels (Bekar et al, 2005). Gnatenco et al (2002) have shown that mRNA for TASK-1, TASK-3, and TREK-2 was present in cultured cortical astrocytes.…”

Electrophysiological properties of NG2 + cells: Matching physiological studies with gene expression profiles

“…Other A-type channel subunits that are highly expressed are K v 4.2, K v 4.3, and Kv3.3. K v 4.2 and 4.3 have been found in neurons (Tsaur et al, 1997) and cultured astrocytes (Bekar et al, 2005), but never previously in oligodendrocyte lineage cells. Kv3.3 has been found in neurons, particularly in the cerebellum and brainstem (Chang et al, 2007), but not in glial cells.…”

A-type K+ currents in intralaminar thalamocortical relay neurons

“…Strong dendritic expression of K V 4.2, which may be based on dendritic localization of K V 4.2 mRNA [22], has also been found in hippocampal and cortical pyramidal cells [37]. None of the neuropil staining of K V 4.2 in intralaminar nuclei results from channel expression in glia cells, although the expression of K V 4.2 in hippocampal reactive glia cells in epilepsyassociated focal lesions [1] and K V 4.3 in hippocampal astrocytes [2] has been found.…”