Non-radioactive Rb Efflux Assay for Screening K Channel Modulators.

ATP-sensitive potassium (K) 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 channels influence a broad spectrum of physiological processes, including insulin secretion and cardiovascular functions. K 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 channel subtypes with distinct tissue distributions and physiological functions. Mutations in the genes encoding K channel subunits underlie various human diseases. Targeted treatment for these diseases requires subtype-specific K channel modulators. Rubidium ions (Rb) also pass through K channels, and Rb efflux assays can be used to assess K 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 channel activity in Rb efflux assays. In this chapter, we describe a detailed protocol for Rb efflux assays designed to identify new K channel modulators with potential therapeutic utilities.