Localization and developmental changes of the expression of two inward rectifying K(+)-channel proteins in the rat...

We have raised affinity-purified polyclonal antibodies specific for the inward rectifying K+ channel (IRK1/Kir2.1) and the G protein-activated inward rectifying K+ channel (GIRK1/Kir3.1) examined their distributions in the rat brain immunohistochemically. The regional expression pattern of the IRK1 and GIRK1 proteins were similar to those of mRNA of the previous in situ hybridization study. The subcellular distribution was studied in the cerebellum; cerebral cortex and hippocampus. In the cerebellum, the IRK1 protein was clearly detected in the somata and proximal dendrites of Purkinje cells, while the GIRK1 protein was present in the somata and clustered dendrites of granule cells. In the cerebral cortex and hippocampus, both IRK1- and GIRK1-immunoreactivities were detected in the somata and apical dendrites of the pyramidal cells. The presence of IRK1 or GIRK1 proteins in the axons could not proved by the present study. The developmental changes of the expression pattern of the GIRK1 protein were also investigated in the hippocampus and in the cerebellum of postnatal day (P) 7 to P17 rats. The GIRK1 protein was detected neither in the subgranular zone of the dentate gyrus nor in the proliferative zone of the external granule cell layer of the cerebellum, in which granule cell precursors are reported to proliferate, while it was clearly detected in the adjacent layer in which postmitotic but immature cells exist. These results imply that the expression of the GIRK1 protein starts just after the neuronal precursors finished the last mitotic cell division.