Complex expression and localization of inactivating Kv channels in cultured hippocampal astrocytes.
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 approximately 70, 10, and <5% 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 TEA-sensitive 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 alpha-subunits with accessory, possibly Ca(2+)-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.
Bekar
Lane K
LK
Department of Physiology, University of Saskatchewan, Rm B39 Health Sciences Bldg, Saskatoon, SK, S7N 5E5, Canada.
Loewen
Matthew E
ME
Cao
Kun
K
Sun
Xianfeng
X
Leis
Jerome
J
Wang
Rui
R
Forsyth
George W
GW
Walz
Wolfgang
W
D015761:4-Aminopyridine / Q000494:pharmacology; D015117:5,8,11,14-Eicosatetraynoic Acid / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D015152:Blotting, Northern / Q000379:methods; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004558:Electric Stimulation / Q000379:methods; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D018408:Patch-Clamp Techniques / Q000379:methods; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024642:Potassium Channels, Voltage-Gated / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D019789:Tetraethylammonium / Q000494:pharmacology; D014162:Transfection / Q000379:methods
D005904:Glial Fibrillary Acidic Protein; D026902:Potassium Channel Blockers; D024642:Potassium Channels, Voltage-Gated; D012333:RNA, Messenger; D015117:5,8,11,14-Eicosatetraynoic Acid; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D002118:Calcium