Immunogold evidence suggests that coupling of K+ siphoning and water transport in rat retinal Müller cells is mediated by a coenrichment of Kir4.1 and AQP4 in specific membrane domains
✍ Scribed by Erlend A. Nagelhus; Yoshiyuki Horio; Atsushi Inanobe; Akikazu Fujita; Finn-m. Haug; Søren Nielsen; Yoshihisa Kurachi; Ole Petter Ottersen
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 526 KB
- Volume
- 26
- Category
- Article
- ISSN
- 0894-1491
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✦ Synopsis
Postembedding immunogold labeling was used to examine the subcellular distribution of the inwardly rectifying K ϩ channel Kir4.1 in rat retinal Mu ¨ller cells and to compare this with the distribution of the water channel aquaporin-4 (AQP4). The quantitative analysis suggested that both molecules are enriched in those plasma membrane domains that face the vitreous body and blood vessels. In addition, Kir4.1, but not AQP4, was concentrated in the basal ϳ300-400 nm of the Mu ¨ller cell microvilli. These data indicate that AQP4 may mediate the water flux known to be associated with K ϩ siphoning in the retina. By its highly differentiated distribution of AQP4, the Mu ¨ller cell may be able to direct the water flux to select extracellular compartments while protecting others (the subretinal space) from inappropriate volume changes. The identification of specialized membrane domains with high Kir4.1 expression provides a morphological correlate for the heterogeneous K ϩ conductance along the Mu ¨ller cell surface.