Presynaptic neurotoxin that blocks the inwardly rectifying Kir1.1/KCNJ1 and Kir3.1/3.4 (KCNJ3/KCNJ5) potassium channels with high affinity by binding to the M1-M2 linker region of these channels in a 1:1 stoichiometry. It may block the potassium channel pore by occluding its alpha helix into the channel vestibule. Tertiapin-Q also inhibits calcium-activated large conductance BK-type (KCNMA) potassium channels in a concentration-, and voltage-dependent manner, in addition to inhibiting Kir3.1/3.2 (KCNJ3/KCNJ6) heteromultimers potassium channels. It can prevent dose-dependently acetylcholine(ACh)-induced atrioventricular blocks in mammalian hearts, as KCNJ3/KCNJ5 channels (also named I(KACh), because these channels are activated by ACh) are found in mammalian myocytes. Interacts specifically with calmodulin in the presence of calcium. Expressed by the venom gland. Oxidation of Met-13 results in the loss of biological activity. An amidation at Lys-21 is suggested in Ref.1. Tertiapin-Q is a stable (non-oxidizable) and functionally similar derivative of tertiapin whose Met-13 residue is replaced with a Gln residue. Tertiapin entry