TWIK-1 and TREK-1 are potassium channels contributing significantly to astrocyte passive conductance in rat hippocampal slices.
Expression of a linear current-voltage (I-V) relationship (passive) K(+) membrane conductance is a hallmark of mature hippocampal astrocytes. However, the molecular identifications of the K(+) channels underlying this passive conductance remain unknown. We provide the following evidence supporting significant contribution of the two-pore domain K(+) channel (K(2P)) isoforms, TWIK-1 and TREK-1, to this conductance. First, both passive astrocytes and the cloned rat TWIK-1 and TREK-1 channels expressed in CHO cells conduct significant amounts of Cs(+) currents, but vary in their relative P(Cs)/P(K) permeability, 0.43, 0.10, and 0.05, respectively. Second, quinine, which potently inhibited TWIK-1 (IC(50) = 85 microm) and TREK-1 (IC(50) = 41 microm) currents, also inhibited astrocytic passive conductance by 58% at a concentration of 200 microm. Third, a moderate sensitivity of passive conductance to low extracellular pH (6.0) supports a combined expression of acid-insensitive TREK-1, and to a lesser extent, acid-sensitive TWIK-1. Fourth, the astrocyte passive conductance showed low sensitivity to extracellular Ba(2+), and extracellular Ba(2+) blocked TWIK-1 channels at an IC(50) of 960 microm and had no effect on TREK-1 channels. Finally, an immunocytochemical study showed colocalization of TWIK-1 and TREK-1 proteins with the astrocytic markers GLAST and GFAP in rat hippocampal stratum radiatum. In contrast, another K(2P) isoform TASK-1 was mainly colocalized with the neuronal marker NeuN in hippocampal pyramidal neurons and was expressed at a much lower level in astrocytes. These results support TWIK-1 and TREK-1 as being the major components of the long-sought K(+) channels underlying the passive conductance of mature hippocampal astrocytes.
Zhou
Min
M
Ordway Research Institute, Albany, New York 12208, USA. mzhou@ordwayresearch.org
Xu
Guangjin
G
Xie
Minjie
M
Zhang
Xuexin
X
Schools
Gary P
GP
Ma
Liqun
L
Kimelberg
Harold K
HK
Chen
Haijun
H
D000818:Animals; D001253:Astrocytes / Q000502:physiology*; D001464:Barium / Q000378:metabolism; D055592:Biophysical Phenomena / Q000502:physiology*; D001703:Biophysics; D016466:CHO Cells; D002586:Cesium / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D004553:Electric Conductivity; D004558:Electric Stimulation / Q000379:methods; D027341:Excitatory Amino Acid Transporter 1 / Q000378:metabolism; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D018698:Glutamic Acid / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000235:genetics; D006624:Hippocampus / Q000166:cytology*; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects / Q000235:genetics; D008239:Lysine / Q000235:genetics; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D009154:Mutation / Q000235:genetics; D009865:Oocytes; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D024683:Potassium Channels, Tandem Pore Domain / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D014162:Transfection / Q000379:methods; D014981:Xenopus
D027341:Excitatory Amino Acid Transporter 1; D005904:Glial Fibrillary Acidic Protein; C487530:Kcnk1 protein, rat; D024683:Potassium Channels, Tandem Pore Domain; C493392:Slc1a3 protein, rat; C103742:potassium channel protein TREK-1; D049452:Green Fluorescent Proteins; D002586:Cesium; D001464:Barium; D018698:Glutamic Acid; D008239:Lysine; D011188:Potassium