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      TWIK-1 and TREK-1 are potassium channels contributing significantly to astrocyte passive conductance in rat hippocampal slices.

      The Journal of neuroscience : the official journal of the Society for Neuroscience
      Animals, Astrocytes, physiology, Barium, metabolism, Biophysical Processes, Biophysics, CHO Cells, Cesium, Cricetinae, Cricetulus, Electric Conductivity, Electric Stimulation, methods, Excitatory Amino Acid Transporter 1, Glial Fibrillary Acidic Protein, Glutamic Acid, genetics, Green Fluorescent Proteins, Hippocampus, cytology, In Vitro Techniques, Ion Channel Gating, drug effects, Lysine, Membrane Potentials, Mutation, Oocytes, Patch-Clamp Techniques, Potassium, Potassium Channels, Tandem Pore Domain, Rats, Transfection, Xenopus

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          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.

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