VU591 is a renal outer medullary potassium channel (ROMK) blocker that selectively inhibits inward rectifier potassium channel, Kir1.1 (IC50 = 240 nM), in HEK-293 cells. At 10 µM, it displays no effect on Kir2.1, Kir2.3, Kir4.1, and Kir7.1, with 150-fold selectivity over Kir6.2. I