Inwardly Rectifying K+ Channel in Retinal Mueller Cells: Comparison with the KAB-2/Kir4.1 Channel Expressed in HEK293T Cells.

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Abstract
Inwardly rectifying K+ (Kir) channels are considered to play the major role in the spatial buffering of glial cells. We have examined the electrophysiological properties of Kir channels in isolated rabbit Müller cells (retinal glial cells). Although a previous study reported that three kinds of Kir channels with different conductance and rectification properties were expressed in distinct regions of rabbit Müller cell membrane, we could record only a single population of Kir channels from the distal end to the endfoot in 205 successful cell-attached patches. The identified Müller cell Kir channel had a unitary conductance of 25 pS in the inward direction with symmetrical 153 mM K+ condition. The conductance and gating properties of the Müller cell Kir channels were identical to those of the KAB-2/Kir4.1 heterologously expressed in a mammalian cultured cell line, HEK293T cells. Thus KAB-2/Kir4.1 was the predominant glial Kir channel not only in the brain, but also in the retina. Because its rectification is intermediate, this Kir channel may contribute to both the intrusion and the extrusion of K+ ions across glial cell membrane and may be the major pathway for redistribution of extracellular K+ ions in the central nervous system.
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