Differential distribution of classical inwardly rectifying potassium channel mRNAs in the brain: comparison of IRK2 with IRK1 and IRK3.

Distribution of IRK2 inwardly rectifying potassium channel mRNA in the mouse brain was studied using in situ hybridization histochemistry and compared with those of other classical inwardly rectifying potassium channel (IRK1 and IRK3) mRNAs. All these IRK channel mRNAs were detected in neurons, but not in glial cells. Their distribution patterns in the brain were, however, quite divergent: IRK2 mRNA was detected extremely high in granule cells of cerebellum, relatively high in motor trigeminal nucleus and moderate in olfactory bulb, piriform cortex, cerebral cortex, CA1 through CA3 regions of hippocampus, dentate gyrus and pontine nucleus. On the other hand, IRK1 mRNA was expressed throughout whole brain but in particular subsets of neurons, and IRK3 mRNA was in forebrain. Expression of these three IRK mRNAs overlapped in hippocampus, olfactory bulb, and cerebral cortex. This differential distribution of IRK mRNAs suggests that each of these channels has its specific function in regulation of the excitability of brain neurons.