Alpha-conotoxin GI is a 13-aa toxin isolated from the cone snail Conus geographus venom. Alpha-conotoxin GI is a potent reversible blocker of the alpha/delta nicotinic acetylcholine channel receptors (nAChR). Alpha-conotoxin GI allows to distinguish between the two agonist sites as it binds 10,000-fold more tightly to the alpha/delta site than the alpha/gamma site excepted in Torpedo which is the reverse.H-Glu-Cys-Cys-Asn-Pro-Ala-Cys-Gly-Arg-His-Tyr-Ser-Cys-NH2 (Cys2-Cys7, Cys3-Cys13) or H-ECCNPACGRHYSC-NH2 (Cys2-Cys7, Cys3-Cys13)