Differential expression and distribution of Kir5.1 and Kir4.1 inwardly rectifying K⁺ channels in retina

Abstract

Kir5.1 is an inwardly rectifying K+ channel subunit whose functional role has not been fully elucidated. Expression and distribution of Kir5.1 in retina were examined with a specific polyclonal antibody. Kir5.1 immunoreactivity was detected in glial Müller cells and in some retinal neurons. In the Kir5.1-positive neurons the expression of glutamic acid decarboxylase (GAD65) was detected, suggesting that they may be GABAergic-amacrine cells. In Müller cells, spots of Kir5.1 immunoreactivity distributed diffusely at the cell body and in the distal portions, where Kir4.1 immunoreactivity largely overlapped. In addition, Kir4.1 immunoreactivity without Kir5.1 was strongly concentrated at the endfoot of Müller cells facing the vitreous surface or in the processes surrounding vessels. The immunoprecipitant obtained from retina with anti-Kir4.1 antibody contained Kir5.1. These results suggest that heterotetrameric Kir4.1/Kir5.1 channels may exist in the cell body and distal portion of Müller cells, whereas homomeric Kir4.1 channels are clustered in the endfeet and surrounding vessels. It is possible that homomeric Kir4.1 and heteromeric Kir4.1/Kir5.1 channels play different functional roles in the K+-buffering action of Müller cells.

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

“…A similar situation exists in retinal Mü ller cells (14,18,40), where the DAPC has been suggested to play a key role in the selective and specific localization of Kir4.1 (22,41). Both Kir4.1 and Kir5.1 possess a PDZ (PSD-95-Disc large-ZO1) domain binding motif at their carboxyl-terminal end and can physically bind to PSD-95 family proteins (21,42).…”

“…Antibodies-Generation of specific antibodies against Kir4.1 (K AB -2C2) and Kir5.1 (Kir5.1-NR1) was as previously described (18,24). Antibodies specific for Kir4.2 (epitope; residues 347-366 of mouse Kir4.2, GenBank TM accession number O88932) and AQP4 (epitope; residues 249 -323 of rat AQP4, GenBank TM accession number P47863) were purchased from Alomone Laboratories (Jerusalem, Israel).…”

“…Kir5.1-We first examined the expression of Kir4.1 and Kir5.1 in the mouse brain using antibodies of established specificity (18,24). In some experiments we also examined the renal expression of Kir4.1 and Kir5.1 for comparison (1,2,32).…”

“…Assembly of Kir4.1 and Kir5.1 has been reported to yield functional Kir channels in renal epithelia (1, 2, 32) and retinal Mü ller cells (18). To see if such heteromeric assembly occurred in the brain, we performed immunoprecipitation with solubilized brain lysate using the antibodies for Kir4.1 or Kir5.1 (Figs.…”

“…A recent immunohistochemical study of the retina has revealed that Mü ller cells express not only homomeric Kir4.1 but also heteromeric Kir4.1/5.1 channels (18). The two Kir channels distributed differentially within a Mü ller cell.…”