(+)-Anatoxin-a Is a Potent Agonist at Neuronal Nicotinic Acetylcholine Receptors

Abstract: The effects of the nicotinic agonist (+)-anatoxin-a have been examined in four different preparations, representing at least two classes of neuronal nicotinic receptors. (+)-Anatoxin-a was most potent (EC₅₀= 48 n M ) in stimulating ⁸⁶Rb⁺ influx into M10 cells, which express the nicotinic receptor subtype comprising α4 and β2 subunits. A presynaptic nicotinic receptor mediating acetylcholine release from hippocampal synaptosomes was similarly sensitive to (+)-anatoxin-a (EC₅₀= 140 n M ). α-Bungarotoxin-sensitive neuronal nicotinic receptors, studied using patch-clamp recording techniques, required slightly higher concentrations of this alkaloid for activation: Nicotinic currents in hippocampal neurons were activated by (+)-anatoxin-a with an EC₅₀ of 3.9 γ M , whereas α7 homooligomers reconstituted in Xenopus oocytes yielded an EC₅₀ value of 0.58 γ M for (+)-anatoxin-a. In these diverse preparations, (+)-anatoxin-a was between three and 50 times more potent than (–)-nicotine and ˜20 times more potent than acetylcholine, making it the most efficacious nicotinic agonist thus far described.