Expression and functional properties of unique inward rectifier K ⁺ channel Kir7.1 in the porcine iris and retinal pigment epithelium

Purpose. To investigate the membrane functional properties of porcine iris pigment epithelial cells (IPE), and compare the characters of inward rectifier potassium (Kir) channel in the IPE with those in the retinal pigment epithelial cells (RPE). Methods. IPE and RPE were acutely dissociated from porcine eyes. Functional properties of Kir channels were characterized using whole cell patch clamp recording techniques. Expression of Kir7.1 mRNA in both cells was detected by reverse transcription-polymerase chain reaction (RT-PCR). Results. Whole cell current in the IPE exhibited a mild inward K⁺ rectification, and showed little dependence on [K⁺]_o. Unusual high (7.04 ± 1.7) Rb⁺ to K⁺ inward conductance ratio indicated that Kir7.1 subunit was expressed in the IPE as the same as RPE cells. Also, Kir7.1 mRNA was detected in both porcine IPE and RPE by RT-PCR. However, functional expression of Kir conductance in IPE cells (21.7 S/F) was much smaller than that in RPE cells (205.6 S/F). Conclusions. The Kir7.1 subunit was predominantly expressed in the acutely dissociated porcine IPE and its functional properties are similar to those in the RPE. However, the current density seems too small to fulfill the task of the Kir function of RPE.