An inwardly rectifying K⁺ channel, Kir4.1, expressed in astrocytes surrounds synapses and blood vessels in brain

Abstract

Glial cells express inwardly rectifying K(+) (Kir) channels, which play a critical role in the buffering of extracellular K(+). Kir4.1 is the only Kir channel so far shown to be expressed in brain glial cells. We examined the distribution of Kir4.1 in rat brain with a specific antibody. The Kir4.1 immunostaining distributed broadly but not diffusely in the brain. It was strong in some regions such as the glomerular layer of the olfactory bulb, the Bergmann glia in the cerebellum, the ependyma, and pia mater, while little activity was detected in white matter of the corpus callosum or cerebellar peduncle. In the olfactory bulb, Kir4.1 immunoreactivity was detected in a scattered manner in about one-half of the glial fibrillary acidic protein-positive astrocytes. Immunoelectron microscopic examination revealed that Kir4.1 channels were enriched on the processes of astrocytes wrapping synapses and blood vessels. These data suggest that Kir4.1 is expressed in a limited population of brain astrocytes and may play a specific role in the glial K(+)-buffering action.

GABA uptake-dependent Ca 2+ signaling in developing olfactory bulb astrocytes

“…We have chosen the olfactory bulb for this study, because astrocytic processes ensheath dendrodendritic, mostly GABAergic synapses (15,16). Our results indicate a principle of GABAergic signaling between neurons and glial cells mediated by GATs.…”

Differential Assembly of Inwardly Rectifying K+ Channel Subunits, Kir4.1 and Kir5.1, in Brain Astrocytes

“…2C). Kir4.1 was moderately expressed in the processes of astrocytes in the pyramidal cell layer and the stratum radiatum (16,17). Relatively weak labeling for Kir5.1 was scattered in or close to the pyramidal cell layer, where it was largely colocalized with the Kir4.1-specific signal.…”

“…Briefly, the bodies of adult female C57BL/6 mice, which were deeply anesthetized with pentobarbital sodium (100 mg/kg), were perfused from their left ventricle with 4% paraformaldehyde, 0.1 M sodium phosphate, pH 7.4, and the brains were isolated. The procedures for double-immunolabeling of slice sections have been previously published (14,16,30,31). In short, cryosections of brain (12 m) were at first incubated with antiKir5.1 (4 g/ml; Figs.…”

“…Immunoelectron Microscopic Examination-Pre-embedding immunoelectron microscopic analysis of mouse brain with either Kir4.1 or Kir5.1 antibody was performed as described previously (16). AntiKir4.1 (6 g/ml) or anti-Kir5.1 (40 g/ml) was used to examine thin sections (thickness, 75ϳ90 nm) of mouse brain neocortex.…”

“…Kir4.1 is abundantly expressed in astrocytes of many brain regions (16,17). We, therefore, compared the distribution of Kir5.1 in mouse brain with that of Kir4.1 by double-immunolabeling (Fig.…”