Pharmacology of Small- and Intermediate-Conductance Calcium-Activated Potassium Channels.

The three small-conductance calcium-activated potassium (K2) channels and the related intermediate-conductance K3.1 channel are voltage-independent K channels that mediate calcium-induced membrane hyperpolarization. When intracellular calcium increases in the channel vicinity, it calcifies the flexible N lobe of the channel-bound calmodulin, which then swings over to the S4-S5 linker and opens the channel. K2 and K3.1 channels are highly druggable and offer multiple binding sites for venom peptides and small-molecule blockers as well as for positive- and negative-gating modulators. In this review, we briefly summarize the physiological role of K channels and then discuss the pharmacophores and the mechanism of action of the most commonly used peptidic and small-molecule K2 and K3.1 modulators. Finally, we describe the progress that has been made in advancing K3.1 blockers and K2.2 negative- and positive-gating modulators toward the clinic for neurological and cardiovascular diseases and discuss the remaining challenges.