Expression and polarized distribution of an inwardly rectifying K+ channel, Kir4.1, in rat retinal pigment epithelium

1. In the eye, different substances and ions including potassium (K+) are t ransported between neural retina and choroid via the subretinal space. Inwa rdly rectifying K+ channels (Kir) on the apical membrane of retinal pigment epithelial (RPE) cells are thought to play an essential role in K+ transpo rt in the subretinal space. 2. Single-channel recordings from the apical membrane of RPE cells exhibite d functional expression of a Kir channel with properties identical to those of Kir4.1, while recordings from the basolateral membrane showed no detect able Kir channel currents. 3. The expression of Kir4.1 mRNA in RPE cells was confirmed by RT-PCR analy sis and in situ hybridization, Furthermore, using immunohistochemistry, we found that Kir4.1 was prominently expressed in RPE cells and localized spec ifically on the processes on their apical membrane. 4. Developmental studies revealed that expression of Kir4.1 started to appe ar 10 days Or later after birth in RPE cells, in parallel with the maturati on of retinal neuronal activity as represented by the a- and b-waves of the electroretinogram. 5. These data suggest that Kir4.1 is one of the Kir channels involved in RP E-mediated control of K+ ions in the subretinal space.