Agonist and antagonist interactions with the nicotinic acetylcholine receptor

Drugs activating the nicotinic acetylcholine receptor (nAChR), a neurotransmitter-gated ion channel, are called agonists, while those preventing its function are called antagonists. By use of electrophysiological techniques to characterize the response of nAChRs expressed in Xenopus oocytes, I found that the efficacies (efficiencies of response relative to the full agonist acetylcholine (ACh)) for selected partial agonists on Torpedo nAChRs varied by 1000-fold, while for the same agonists on mouse nAChRs they varied by 10-fold. In addition, thiocholine tethered at gammaE57C near the ACh binding site in a mutant Torpedo nAChR appeared to prevent agonist binding, while for mouse gammaE57C nAChR it altered agonist gating. Quantitative analyses of the data in terms of nAChR gating models showed that the differences in agonist responses could be explained simply by the differences between species of the stability of the nAChR closed states.; Azietomidate is a photoactivatible non-competitive antagonist that binds to the nAChR desensitized state with 10-fold higher affinity than the closed state (Ziebell et al., 2004). In electrophysiological studies of Torpedo nAChRs in whole oocytes and in excised patches, I found that azietomidate acts as a nAChR open state inhibitor. Azietomidate appeared to accelerate ACh-dependent desensitization, but the kinetics of recovery from desensitization showed that azietomidate-driven inhibition was distinct from ACh-dependent desensitization. Azietomidate did not alter the equilibrium between open and desensitized states.; The crystal structure of the acetylcholine binding protein (AChBP; Brejc et al., 2001) has served as a basis for homology models of the nAChR extracellular domain. However, some nAChR amino acids identified as agonist/antagonist affinity determinants are in regions of primary structure not present in the AChBP. The substituted cysteine accessibility method was used to characterize the functional importance of amino acids in such a region of the nAChR gamma and delta subunits, as well as the corresponding region in alpha subunit. These studies identified alphaE175, which is predicted to be 30 A from the ACh binding site, as an agonist gating determinant important for the transduction mechanism that connects agonist binding to channel gating.