Abstract

The nicotinic acetylcholine receptor (nAChR) α9 and α10 subunits are expressed primarily within hair cells of the inner ear and have been implicated in auditory processing. Although functional recombinant nAChRs generated by the coexpression of α9 and α10 in Xenopus laevis oocytes have been described previously, there have been no reports of the successful heterologous expression of α9α10 nAChRs in cultured cell lines. In this study, subunit chimeras (α9χ and α10χ) have been constructed that contain the extracellular, ligand binding domain of the α9 or α10 subunits fused to the C-terminal domain of the 5-hydroxytryptamine type 3A (5HT_3A) subunit. Specific high-affinity binding of the nicotinic radioligand [³H]methyllycaconitine was detected in membrane preparations of mammalian cells transfected with α9χ or α10χ alone, but significantly higher levels of binding were detected when α9χ and α10χ were cotransfected, providing evidence of a requirement for coassembly of α9 and α10 for the efficient formation of a nicotinic binding site. The pharmacological profile of α9χα10χ receptors, determined by equilibrium radioligand binding studies, is broadly similar to that determined previously by electrophysiological studies conducted with native and recombinant α9α10 nAChRs. In agreement with evidence that α9α10 nAChRs exhibit an atypical pharmacological profile, we have identified specific high-affinity binding of several non-nicotinic ligands including strychnine (a glycine receptor antagonist), bicuculline (a GABA_A receptor antagonist), and atropine (a muscarinic acetylcholine receptor antagonist). Results have also been compared with radioligand binding data conducted with a previously described α7/5HT_3A (α7χ) subunit chimera.