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. {ECO:0000269|PubMed:20074522, ECO:0000269|PubMed:27008341}. This is the function of KCNJ18 (potassium inwardly rectifying channel subfamily J member 18, ENSG00000260458).