Kidney Function

The inwardly rectifying K+ (Kir) current in mammalian retinal pigment epithelial (RPE) cells, which is largely mediated by Kir7.1 channels, is stable in cells dialyzed with MgATP but runs down when intracellular ATP is depleted. A potential mechanism for this rundown is a decrease in phosphatidylinositol 4,5-bisphosphate (PIP2) regeneration by ATP-dependent lipid kinases. Here, we used the whole cell voltage-clamp technique to investigate the membrane PIP2 dependence of Kir channels in isolated bovine RPE cells. When RPE cells were dialyzed with ATP-free solution containing PIP2 (25–50 µM), rundown persisted but was markedly reduced. Removal of Mg2+ from the pipette solution also slowed rundown, indicating that elevated intracellular Mg2+ concentration contributes to rundown. C…

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