Subtype-selective inhibition of neuronal nicotinic acetylcholine receptorsby cocaine is determined by the alpha 4 and beta 4 subunits

Neuronal nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion ch annels of the central and peripheral nervous system that regulate synaptic activity from both pre- and postsynaptic sites. Nicotine binding to brain n AChRs is thought to underlie the induction of behavioral addiction to nicot ine, probably as a result of desensitizing/inhibitory effects. Here, anothe r commonly abused drug, cocaine, is shown to selectively inhibit particular nAChR subtypes with a potency in the low micromolar range by interacting w ith separate sites associated with the alpha 4 and beta 4 nAChR subunits. C himeric receptor subunits and site-directed mutants were used to localize s equence determinants of cocaine affinity to: 1) a region of alpha 4 located between residues 128 and 267 and 2) a site within the pore-lining M2 domai n of beta 4 that includes the 13' phenylalanine residue. The voltage depend ence for inhibition associated with each site is consistent with these resu lts. Analysis of the effects of incorporation of mutant and chimeric subuni ts also permitted identification of sequence elements important in receptor activation. For alpha 3-containing receptors, a region or regions containe d within the N-terminal extracellular domain of neuronal beta subunits infl uence the time course of responses to acetylcholine. Conversely, the 13' re sidue of the beta 4 subunit M2 region is important in determining acetylcho line potency, indicating a role for this residue in agonist binding/gating processes. In summary, the present work describes sequence elements critica l in both cocaine inhibition and acetylcholine activation of nAChRs and ind icates that nAChRs may provide a site of interaction for the effects of nic otine and cocaine in the nervous system.