The specific aim of this project is to identify small molecule inhibitors of Renal Outer Medullary Potassium Channel (ROMK, Kir1.1, KCNJ1), a potassium channel located in the renal tubule, where it critically regulates sodium and potassium balance. However, due to the lack of selective small molecule inhibitors of ROMK, the molecular pharmacology of ROMK, and indeed that of the entire inward rectifier K+ channel family (kir), is undeveloped, precluding assessment of ROMK's potential as a diuretic target. Furthermore, at least 6 other members (Kir2.3, Kir4.1, Kir4.2, Kir5.1, Kir7.1) of the Kir channel family are expressed in the nephron, but their physiological functions are not well understood. The project aimed to develop ROMK inhibitors with submicromolar potency, cell penetrance and greater than 10-fold selectivity versus other members of the Kir channel family (Kir2.3, Kir4.1, Kir4.2, Kir5.1 and Kir7.1). The currently identified probe, ML112 (CID-44123657) can be used for in vitro and electrophysiology studies to probe the role of ROMK inhibition without inhibition of closely related channels Kir2.1, Kir4.1, Kir7.1, Kir2.3, or hERG. Moreover a PanLab screen identified no significant ancillary pharmacology, thus ML112 is the first truly selective small molecule inhibitor of ROMK, and can be employed to study ROMK with confidence. This is the second probe from this screening effort, the first being ML111 (CID-4536383), a ROMK inhibitor that also is the first known inhibitor of Kir7.1.