Apamin is an 18 amino acid peptide toxin found in bee venom. It is a potent blocker of small conductance Ca2+-activated K+ (SK, KCa2) channels that is more effective at SK2 than SK1 and SK3 (IC50 values are 0.06-0.4, 1-12, and 1-13 nM, respectively). It is ineffective against SK4 at 1 μM. Apamin is used to elucidate the roles of these channels in cells and tissues expressing SK channels, including neurons, vascular endothelium, bladder smooth muscle, and certain types of cancer cells.
