Analysis of astroglial K+ channel expression in the developing hippocampus reveals a predominant role of the Kir4.1 subunit.
Astrocytes in different brain regions display variable functional properties. In the hippocampus, astrocytes predominantly express time- and voltage-independent currents, but the underlying ion channels are not well defined. This ignorance is partly attributable to abundant intercellular coupling of these cells through gap junctions, impeding quantitative analyses of intrinsic membrane properties. Moreover, distinct types of cells with astroglial properties coexist in a given brain area, a finding that confused previous analyses. In the present study, we investigated expression of inwardly rectifying (Kir) and two-pore-domain (K2P) K+ channels in astrocytes, which are thought to be instrumental in the regulation of K+ homeostasis. Freshly isolated astrocytes were used to improve space-clamp conditions and allow for quantitative assessment of functional parameters. Patch-clamp recordings were combined with immunocytochemistry, Western blot analysis, and semiquantitative transcript analysis. Comparative measurements were performed in different CA1 subregions of astrocyte-targeted transgenic mice. While confirming weak Ba2+ sensitivity in situ, our data demonstrate that in freshly isolated astrocytes, the main proportion of membrane currents is sensitive to micromolar Ba2+ concentrations. Upregulation of Kir4.1 transcripts and protein during the first 10 postnatal days was accompanied by a fourfold increase in astrocyte inward current density. Hippocampal astrocytes from Kir4.1-/- mice lacked Ba2+-sensitive currents. In addition, we report functional expression of K2P channels of the TREK subfamily (TREK1, TREK2), which mediate astroglial outward currents. Together, our findings demonstrate that Kir4.1 constitutes the pivotal K+ channel subunit and that superposition of currents through Kir4.1 and TREK channels underlies the "passive" current pattern of hippocampal astrocytes.
Seifert
Gerald
G
Institute of Cellular Neurosciences, University of Bonn, D-53105 Bonn, Germany.
Hüttmann
Kerstin
K
Binder
Devin K
DK
Hartmann
Christian
C
Wyczynski
Alexandra
A
Neusch
Clemens
C
Steinhäuser
Christian
C
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology*; D001464:Barium / Q000494:pharmacology; D017609:Barium Compounds / Q000494:pharmacology; D002229:Carbenoxolone / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D017630:Connexins / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D017629:Gap Junctions / Q000187:drug effects; D006624:Hippocampus / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000378:metabolism*; D024683:Potassium Channels, Tandem Pore Domain / Q000378:metabolism*; D011803:Quinine / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D000098854:Kcnj10 Channel
D017609:Barium Compounds; D002712:Chlorides; D017630:Connexins; D000098854:Kcnj10 Channel; C503445:Kcnk10 protein, mouse; D026902:Potassium Channel Blockers; D024661:Potassium Channels, Inwardly Rectifying; D024683:Potassium Channels, Tandem Pore Domain; D012333:RNA, Messenger; C103742:potassium channel protein TREK-1; C024986:barium chloride; D001464:Barium; D011803:Quinine; D002229:Carbenoxolone