TWIK-1 and TREK-1 Are Potassium Channels Contributing Significantly to Astrocyte Passive Conductance in Rat Hippocampal Slices

• Published in: The Journal of neuroscience 2009-07, Vol.29 (26), p.8551-8564
• Main Authors: Zhou, Min, Xu, Guangjin, Xie, Minjie, Zhang, Xuexin, Schools, Gary P, Ma, Liqun, Kimelberg, Harold K, Chen, Haijun
• Format: Article
• Language: English
• Subjects: Animals; Astrocytes - physiology; Barium - metabolism; Biophysical Phenomena - physiology; Biophysics; Cesium - metabolism; CHO Cells; Cricetinae; Cricetulus; Electric Conductivity; Electric Stimulation - methods; Excitatory Amino Acid Transporter 1 - metabolism; Glial Fibrillary Acidic Protein - metabolism; Glutamic Acid - genetics; Green Fluorescent Proteins - genetics; Hippocampus - cytology; In Vitro Techniques; Ion Channel Gating - drug effects; Ion Channel Gating - genetics; Lysine - genetics; Membrane Potentials - drug effects; Membrane Potentials - genetics; Mutation - genetics; Oocytes; Patch-Clamp Techniques; Potassium - metabolism; Potassium Channels, Tandem Pore Domain - genetics; Potassium Channels, Tandem Pore Domain - metabolism; Rats; Transfection - methods; Xenopus
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/JNEUROSCI.5784-08.2009

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.