Functional expression of Kir4.1 channels in spinal cord astrocytes

✍ Scribed by M.L. Olsen; H. Higashimori; S.L. Campbell; J.J. Hablitz; H. Sontheimer

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 641 KB
• Volume: 53
• Category: Article
• ISSN: 0894-1491
• DOI: 10.1002/glia.20312

✦ Synopsis

Abstract

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 K~ir~4.1 subunit are responsible for mediating the resting K^+^ conductance in SCA. Biophysical analysis demonstrates astrocytic K~ir~ currents as weakly rectifying, potentiated by increasing [K^+^]~o~, and inhibited by micromolar concentrations of Ba^2+^. These currents were insensitive to tolbutemide, a selective blocker of K~ir~6.x channels, and to tertiapin, a blocker for K~ir~1.1 and K~ir~3.1/3.4 channels. PCR and Western blot analysis show prominent expression of K~ir~4.1 in SCA, and immunocytochemistry shows localization K~ir~4.1 channels to the plasma membrane. K~ir~4.1 protein levels show a developmental upregulation in vivo that parallels an increase in currents recorded over the same time period. K~ir~4.1 is highly expressed throughout most areas of the gray matter in spinal cord in vivo and recordings from spinal cord slices show prominent K~ir~ currents. Electrophysiological recordings comparing SCA of wild‐type mice with those of homozygote K~ir~4.1 knockout mice confirm a complete and selective absence of K~ir~ channels in the knockout mice, suggesting that K~ir~4.1 is the principle channel mediating the resting K^+^ conductance in SCA in vitro and in situ. © 2005 Wiley‐Liss, Inc.