Selective IKACh blocker.

Tertiapin is a peptide found in the venom of the European honey bee (Apis mellifera). Tertiapin is a selective inhibitor of the G-protein-gated atrial K+ channel IKACh that can prolong atrial effective refractory period and terminate atrial fibrillation. Tertiapin is also a selective and potent inhibitor of muscarinic K+ channels in rabbit cardiac myocytes. The methionine residue at position 13 of tertiapin is sensitive to oxidation, reducing ability to block ion channels, so the methionine may be substituted by glutamine in order to prevent oxidation, resulting in tertiapin-Q, which shows no functional chan and is a more suitable research tool for some applications.