The alpha 9 nicotinic acetylcholine receptor shares pharmacological properties with type a gamma-aminobutyric acid, glycine, and type 3 serotonin receptors

In the present study, we provide evidence that the alpha 9 nicotinic acetyl choline receptor (nAChR) shares pharmacological properties with members of the Cys-loop family of receptors. Thus, the type A gamma-aminobutyric acid receptor antagonist bicuculline, the glycinergic antagonist strychnine, and the type 3 serotonin receptor antagonist ICS-205,930 block ACh-evoked curr ents in alpha 9-injected Xenopus laevis oocytes with the following rank ord er of potency: strychnine > ICS-205,930 > bicuculline. Block by antagonists was reflected in an increase in the acetylcholine (ACh) EC50 value, with n o changes in agonist maximal response or Hill coefficient, which suggests a competitive type of block. Moreover, whereas neither gamma-aminobutyric ac id nor glycine modified ACh-evoked currents, serotonin blocked responses to ACh in a concentration-dependent manner. The present results suggest that the alpha 9 nAChR must conserve in its primary structure some residues resp onsible for ligand binding common to other Cys-loop receptors. In addition, it adds further evidence that the alpha 9 nAChR and the cholinergic recept or present at the base of cochlear outer hair cells have similar pharmacolo gical properties.