In the kidney, probably plays a major role in potassium homeostasis. Inward rectifier potassium channels are characterized by a greater tendency to allow potassium to flow into the cell rather than out of it. Their voltage dependence is regulated by the concentration of extracellular potassium; as external potassium is raised, the voltage range of the channel opening shifts to more positive voltages. The inward rectification is mainly due to the blockage of outward current by internal magnesium. This channel is activated by internal ATP and can be blocked by external barium. Inhibited by WNK3. Interacts with SGK1 and SLC9A3R2/NHERF2. Phosphorylation at Ser-44 by SGK1 is necessary for its expression at the cell membrane. Mainly in kidney (renal cortex, medulla and papilla). In the brain, found in the cortex and the hippocampus. Phosphorylation at Ser-44 by SGK1 is necessary for its expression at the cell membrane. Belongs to the inward rectifier-type potassium channel (TC 1.A.2.1) family. KCNJ1 subfamily.