Lack of the Kir4.1 channel subunit abolishes K+ buffering properties of astrocytes in the ventral respiratory group: impact on extracellular K+ regulation.
Ongoing rhythmic neuronal activity in the ventral respiratory group (VRG) of the brain stem results in periodic changes of extracellular K+. To estimate the involvement of the weakly inwardly rectifying K+ channel Kir4.1 (KCNJ10) in extracellular K+ clearance, we examined its functional expression in astrocytes of the respiratory network. Kir4.1 was expressed in astroglial cells of the VRG, predominantly in fine astrocytic processes surrounding capillaries and in close proximity to VRG neurons. Kir4.1 expression was up-regulated during early postnatal development. The physiological role of astrocytic Kir4.1 was studied using mice with a null mutation in the Kir4.1 channel gene that were interbred with transgenic mice expressing the enhanced green fluorescent protein in their astrocytes. The membrane potential was depolarized in astrocytes of Kir4.1-/- mice, and Ba2+-sensitive inward K+ currents were diminished. Brain slices from Kir4.1-/- mice, containing the pre-Bötzinger complex, which generates a respiratory rhythm, did not show any obvious differences in rhythmic bursting activity compared with wild-type controls, indicating that the lack of Kir4.1 channels alone does not impair respiratory network activity. Extracellular K+ measurements revealed that Kir4.1 channels contribute to extracellular K+ regulation. Kir4.1 channels reduce baseline K+ levels, and they compensate for the K+ undershoot. Our data indicate that Kir4.1 channels 1) are expressed in perineuronal processes of astrocytes, 2) constitute the major part of the astrocytic Kir conductance, and 3) contribute to regulation of extracellular K+ in the respiratory network.
Neusch
Clemens
C
Dept. of Neurology, Georg-August-Univ. Göttingen, Humboldtallee 23, 37073 Göttingen, Germany.
Papadopoulos
Nestoras
N
Müller
Michael
M
Maletzki
Iris
I
Winter
Stefan M
SM
Hirrlinger
Johannes
J
Handschuh
Melanie
M
Bähr
Mathias
M
Richter
Diethelm W
DW
Kirchhoff
Frank
F
Hülsmann
Swen
S
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001253:Astrocytes / Q000502:physiology*; D001683:Biological Clocks / Q000502:physiology*; D001693:Biological Transport, Active / Q000502:physiology; D002478:Cells, Cultured; D045604:Extracellular Fluid / Q000378:metabolism; D005246:Feedback / Q000502:physiology; D008526:Medulla Oblongata / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D011188:Potassium; D024661:Potassium Channels, Inwardly Rectifying / Q000172:deficiency* / Q000235:genetics; D021122:Protein Subunits; D015656:Respiratory Mechanics / Q000502:physiology*; D000098854:Kcnj10 Channel
D000098854:Kcnj10 Channel; D024661:Potassium Channels, Inwardly Rectifying; D021122:Protein Subunits; D011188:Potassium