Functional expression of Kir4.1 channels in spinal cord astrocytes
Article first published online: 20 DEC 2005
Copyright © 2005 Wiley-Liss, Inc.
Volume 53, Issue 5, pages 516–528, 1 April 2006
How to Cite
Olsen, M.L., Higashimori, H., Campbell, S.L., Hablitz, J.J. and Sontheimer, H. (2006), Functional expression of Kir4.1 channels in spinal cord astrocytes. Glia, 53: 516–528. doi: 10.1002/glia.20312
- Issue published online: 19 JAN 2006
- Article first published online: 20 DEC 2005
- Manuscript Accepted: 28 OCT 2005
- Manuscript Received: 15 OCT 2005
- National Institutes of Health. Grant Numbers: RO1-NS36692, RO1-NS31234, 2 P30 HD 038985
- inward rectifier potassium channel;
- potassium buffering;
- spinal cord
Spinal cord astrocytes (SCA) have a high permeability to K+ and hence have hyperpolarized resting membrane potentials. The underlying K+ channels are believed to participate in the uptake of neuronally released K+. These K+ channels have been studied extensively with regard to their biophysics and pharmacology, but their molecular identity in spinal cord is currently unknown. Using a combination of approaches, we demonstrate that channels composed of the Kir4.1 subunit are responsible for mediating the resting K+ conductance in SCA. Biophysical analysis demonstrates astrocytic Kir currents as weakly rectifying, potentiated by increasing [K+]o, and inhibited by micromolar concentrations of Ba2+. These currents were insensitive to tolbutemide, a selective blocker of Kir6.x channels, and to tertiapin, a blocker for Kir1.1 and Kir3.1/3.4 channels. PCR and Western blot analysis show prominent expression of Kir4.1 in SCA, and immunocytochemistry shows localization Kir4.1 channels to the plasma membrane. Kir4.1 protein levels show a developmental upregulation in vivo that parallels an increase in currents recorded over the same time period. Kir4.1 is highly expressed throughout most areas of the gray matter in spinal cord in vivo and recordings from spinal cord slices show prominent Kir currents. Electrophysiological recordings comparing SCA of wild-type mice with those of homozygote Kir4.1 knockout mice confirm a complete and selective absence of Kir channels in the knockout mice, suggesting that Kir4.1 is the principle channel mediating the resting K+ conductance in SCA in vitro and in situ. © 2005 Wiley-Liss, Inc.