Abstract
An inwardly rectifying K+ channel, Kir5.1, is expressed abundantly in brain but its functional role is still largely unknown. Because Kir5.1 is coexpressed with Kir4.1 in retinal Muller cells, in this study we have compared the biochemical and immunological properties of Kir5.1 and Kir4.1 in the brain. We have found that not only Kir4.1 but also Kir5.1 are expressed mainly in brain astrocytes. These two Kir subunits differentially assemble in a region-specific manner: the heteromer of Kir4.1/Kir5.1 was identified in the areas such as neocortex and glomerulus of olfactory bulb, while the homomer of Kir4.1 was in those such as hippocampus and thalamus. The homomeric assembly of Kir5.1 was not identified. The Kir4.1/Kir5.1 and Kir4.1 channels in astoryctes were concentrated on the membrane facing pia and blood vessels as well as at the processes surrounding synapses. Because each multimer exhibits a unique channel property, homomeric Kir4.1- and heteromeric Kir4.1/Kir5.1-channels may play differential roles in the K+-buffering action of brain astrocytes. In addition, we found that these Kir channels could associate with a PDZ-domain containing protein, syntrophins, which are components of the dystrophin-accociated protein complex (DAPC). Because DAPC has been suggested to regulate the polarized distribution of Kir4.1, the syntrophins may be involved in targeting the Kir channels to selected membrane-domains in the astrocytes. [Jpn J Physiol 54 Suppl:S132 (2004)]
