title: Presence of multiple binding sites on α9α10 nAChR receptors alludes to stoichiometric-dependent action of the α-conotoxin, Vc1.1.
abstract: Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels involved in fast synaptic transmission. nAChRs are pentameric receptors formed from a combination of different or similar subunits to produce heteromeric or homomeric channels. The heteromeric, α9α10 nAChR subtype is well-known for its role in the auditory system, being expressed in cochlear hair cells. These nAChRs have also been shown to be involved in immune-modulation. Antagonists of α9α10 nAChRs, like the α-conotoxin Vc1.1, have analgesic effects in neuropathic pain. Unlike other nAChR subtypes there is no evidence that functional receptor stoichiometries of α9α10 exist. By using 2-electrode voltage clamp methods and maintaining a constant intracellular Ca(2+) concentration, we observed a biphasic activation curve for ACh that is dependent on receptor stoichiometry. Vc1.1, but not the α9α10 antagonists RgIA or atropine, inhibits ACh-evoked currents in a biphasic manner. Characteristics of the ACh and Vc1.1 activation and inhibition curves can be altered by varying the ratio of α9 and α10 mRNA injected into oocytes, changing the curves from biphasic to monophasic when an excess of α10 mRNA is used. These results highlight the difference in the pharmacological profiles of at least two different α9α10 nAChR stoichiometries, possibly (α9)₃(α10)₂ and (α9)₂(α10)₃. As a result, we infer that there is an additional binding site for ACh and Vc1.1 at the α9-α9 interface on the hypothesized (α9)₃(α10)₂ nAChR, in addition to the α10-α9 and or α9-α10 interfaces that are common to both stoichiometries. This study provides further evidence that receptor stoichiometry contributes another layer of complexity in understanding Cys-loop receptors.
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney 2006, NSW, Australia.
authors.forename: Dinesh C
authors.initials: DC
authors.lastname: Indurthi
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney 2006, NSW, Australia.
authors.forename: Elena
authors.initials: E
authors.lastname: Pera
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney 2006, NSW, Australia.
authors.forename: Hye-Lim
authors.initials: HL
authors.lastname: Kim
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney 2006, NSW, Australia.
authors.forename: Cindy
authors.initials: C
authors.lastname: Chu
authors.affiliation: Research School of Chemistry, Australian National University, Canberra 0200, ACT, Australia.
authors.forename: Malcolm D
authors.initials: MD
authors.lastname: McLeod
authors.affiliation: George E. Wahlen Veterans Affairs Medical Center, Salt Lake City, UT 84108, USA; Departments of Psychiatry and Biology, University of Utah, Salt Lake City, UT 84112, USA.
authors.forename: J Michael
authors.initials: JM
authors.lastname: McIntosh
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney 2006, NSW, Australia. Electronic address: nathan.absalom@sydney.edu.au.
authors.forename: Nathan L
authors.initials: NL
authors.lastname: Absalom
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney 2006, NSW, Australia. Electronic address: maryc@pharm.usyd.edu.au.
authors.forename: Mary
authors.initials: M
authors.lastname: Chebib
mesh_terms: D000328:Adult; D000818:Animals; D001665:Binding Sites; D020916:Conotoxins / Q000378:metabolism / Q000494:pharmacology*; D005260:Female; D006801:Humans; D008839:Microelectrodes; D011978:Receptors, Nicotinic / Q000378:metabolism* / Q000502:physiology; D014982:Xenopus laevis
chemical_list: D020916:Conotoxins; D011978:Receptors, Nicotinic; C507383:alpha-conotoxin Vc1.1
keywords: Alpha9alpha10; Nicotinic acetylcholine receptors; RgIA; Subunit stoichiometry; Vc1.1; α-Conotoxins