Development of a Novel Cell-Based Assay System for High-Throughput Screening of Compounds Acting on Background Two-Pore Domain K+ Channels. 
Two-pore domain K+ (K2P) channels are thought to be druggable targets.  However, only a few agents specific for K2P channels have been identified, presumably due to the lack of an efficient screening system.  To develop a new high-throughput screening (HTS) system targeting these channels, we have established a HEK293-based "test cell" expressing a mutated Na+ channel (Nav1.5) with markedly slowed inactivation, as well as a K+ channel (Kir2.1) that sets the membrane potential quite negative, close to K+ equilibrium potential.  We found in this system that Kir2.1 block by 100 μM Ba2+ application consistently elicited a large depolarization like a long-lasting action potential.  This maneuver resulted in cell death, presumably due to the sustained Na+ influx.  When either the TWIK-related acid-sensitive K+ (TASK)-1 or TASK-3 channel was expressed in the test cells, Ba2+-induced cell death was markedly weakened.  Stronger activation of TASK-1 by extracellular acidification further decreased the cell death.  In contrast, the presence of K2P channel blockers enhanced cell death.  IC50 values for TASK-1 and/or TASK-3 blockers acquired by measurements of relative cell viability were comparable to those obtained using patch-clamp recordings.  Both blockers and openers of K2P channels can be accurately assessed with high efficiency and throughput by this novel HTS system.