Non-radioactive Rb⁺ Efflux Assay for Screening K_ATP Channel Modulators

ATP-sensitive potassium (K_ATP) channels function as metabolic sensors that link cell membrane excitability to the cellular energy status by controlling potassium ion (K⁺) flow across the cell membrane according to intracellular ATP and ADP concentrations. As such, K_ATP channels influence a broad spectrum of physiological processes, including insulin secretion and cardiovascular functions. K_ATP channels are hetero-octamers, consisting of four inward rectifier potassium channel subunits, Kir6.1 or Kir6.2, and four sulfonylurea receptors (SURs), SUR1, SUR2A, or SUR2B. Different Kir6 and SUR isoforms assemble into K_ATP channel subtypes with distinct tissue distributions and physiological functions. Mutations in the genes encoding K_ATP channel subunits underlie various human diseases. Targeted treatment for these diseases requires subtype-specific K_ATP channel modulators. Rubidium ions (Rb⁺) also pass through K_ATP channels, and Rb⁺ efflux assays can be used to assess K_ATP channel function and activity. Flame atomic absorption spectroscopy (Flame-AAS) combined with microsampling can measure Rb⁺ in small volume, which provides an efficient tool to screen for compounds that alter K_ATP channel activity in Rb⁺ efflux assays. In this chapter, we describe a detailed protocol for Rb⁺ efflux assays designed to identify new K_ATP channel modulators with potential therapeutic utilities.