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K Yasuda, M Shimura, H Tomita, E Sugano, T Nakazawa, M Tamai; Functional Properties of Inward Rectifier Potassium Channel in Porcaine Iris Pigment Epithelium . Invest. Ophthalmol. Vis. Sci. 2002;43(13):718.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:In the clinical treatment for retinal degenerative disease, iris pigment epithelial cells (IPE) are possible substitutes for retinal pigment epithelial cells (RPE) for transplantation into the subretinal space. It was known that inward rectifier potassium (Kir) channel in the RPE has unique properties that distinguish from other Kir channels. However its function in the IPE was not known. Thus the functional properties of the porcaine IPE were investigated, and compared to that in RPE. Methods:Whole cell currents in freshly isolated porcaine IPE were recorded using the patch clamp technique with 135 mM K+ and 4 mM ATP in the pipette. Kir currents were measured as the Ba2+-sensitive components. To investigate the permeability and conductance sequence for K+ and Rb+, permeability ratio (PRb/PK) calculated from the change in reversal potential produced by replacing 140 mM K+ in the bath with 140 mM Rb+, and the relative inward conductance (GRb/GK) based on the chord conductance for each cation at -150 mV was measured. Results: IPE exhibited a mild inward rectifying K+ current in the presence of 5 mM [K+]o and most of this inward current was blocked by 10 mM Ba2+. The zero current potential (V0) was -74.2 ± 5.9 mV (n=8). In the presence of 140 mM [K+]o,V0 was shifted to -4.3 ± 2.9 mV. Replacement of K+ with Rb+ left V0 virtually unchanged (PRb/PK was 0.93 ± 0.02). In contrast, inward conductance of 140 mM [Rb+]o was greater than that of 140 mM [K+]o (GRb/GK at -150 mV indicated 6.87 ± 1.72). Conclusion: In this study, functional membrane properties in freshly isolated IPE were firstly showed and Kir channel in the IPE had unique properties of mild rectification for 5 mM K+ and unusual high conductance for 140 mM Rb+ that are characteristic of RPE. These results suggested that IPE have some of the functions in RPE, and thus supported the idea that IPE cells are possibly transplanted into the subretinal space substituting for RPE cells in the treatment for retinal degenerative diseases such as age-related macular degeneration.
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