(-ANATOXIN-A IS A POTENT AGONIST AT NEURONAL NICOTINIC ACETYLCHOLINE-RECEPTORS())

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 = 4 8 nM) in stimulating Rb-86+ influx into M 10 cells, which express the nicotinic receptor subtype comprising alpha4 and beta2 subunits. A pre synaptic nicotinic receptor mediating acetylcholine release from hippo campal synaptosomes was similarly sensitive to (+)-anatoxin-a (EC50 = 140 nM). Alpha-Bungarotoxin-sensitive neuronal nicotinic receptors, st udied 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 muM, whereas alpha7 homooligomers reconstituted in Xenopus oocytes yielded an EC50 value of 0.58 muM for (+)-anatoxin-a. In these divers e preparations, (+)-anatoxin-a was between three and 50 times more pot ent than (-)-nicotine and approximately 20 times more potent than acet ylcholine, making it the most efficacious nicotinic agonist thus far d escribed.