Thallium Flux Assay: The ROMK channel functional thallium flux assay is performed in 384 wells, using the FLIPR-Tetra instrument. HEK-hKir1.1 cells are seeded in Poly-D-Lysine microplates and kept in a 37° C.-10% CO2 incubator overnight. On the day of the experiment, the growth media is replaced with the FluxOR reagent loading buffer and incubated, protected from light, at ambient temperature (23-25° C.) for 90 min. The loading buffer is replaced with assay buffer+/-test compound followed by 30 min incubation at ambient temperature, where the Thallium/Potassium stimulant is added to the microplate.Step Protocol 1. Seed HEK-hKir1.1 cells (50 uA at 20,000 cells/well) in 384-well PDL coated Microplates 2. Allow cells to adhere overnight in humidified 37° C./10% CO2 incubator 3. Completely remove cell growth media from microplate and replace with 25 ul loading buffer 4. Incubate Microplate at room temperature, protected form light, for 90 min.
Electrophysiology Assay: Block of Kir1.1 (ROMK1) currents was examined by whole cell voltage clamp (Hamill et. al. Pfluegers Archives 391:85-100 (1981)) using the IonWorks Quattro automated electrophysiology platform (Molecular Devices, Sunnyvale, Calif.). Chinese hamster ovary cells stably expressing Kir1.1 channels were maintained in T-75 flasks in cell culture media in a humidified 10% CO2 incubator at 37° C. Prior to an experiment, Kir1.1 expression was induced by overnight incubation with 1 mM sodium butyrate. On the day of the experiment, cells were dissociated with 2.5 mL of Versene (Invitrogen 15040-066) for approximately 6 min at 37° C. and suspended in 10 mL of bath solution containing (in mM): 150 NaCl, 10 KCl, 2.7 CaCl2, 0.5 MgCl2, 5 HEPES, pH 7.4. After centrifugation, the cell pellet was resuspended in approximately 4.0 mL of bath solution and placed in the IonWorks instrument. The intracellular solution consisted of (in mM): 80 K gluconate, 40 KCl, 20 KF, 3.2 MgCl2, 3 EGTA, 5 Hepes, pH 7.4.