Fluorescence-Based Tl+Influx Assays as a Novel Approach for Characterization of Small-Conductance Ca2+Activated K+ Channel Modulators

Small-conductance Ca²⁺ −activated potassium (SK) channels constitute a family of ion channels that are regulated by the cytosolic Ca²⁺ concentration. Increases in the intracellular Ca²⁺ concentration ([Ca²⁺ ]_i ) result in opening of the channels, which in turn will lead to changes in the membrane potential. As the name implies, the channels are of small conductance, but even so, they are known to play a crucial role in several physiological processes, such as modulation of neurotransmitter and hormone secretion, as well as memory and learning (e.g.,see Curr Med Chem 14:1437–1457, 2007). Owing to the central role of SK channels, they have attracted much attention as potential drug targets, both with respect to identification of activators and blockers of SK channel activity for indications such as, e.g., epilepsy, pain, and urinary incontinence (see Curr Med Chem 14:1437–1457, 2007; Curr Pharm Des 12:397–406, 2006). Thus, great efforts have been put into the development of robust high-throughput assays for detection and characterization of modulators of SK channel activity. In the present chapter, we describe two fluorescence-based Tl⁺ influx assays for detection of positive and negative SK channel modulators.