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The Journal of Neuroscience, November 23, 2005, 25(47):10905-10912; doi:10.1523/JNEUROSCI.3805-05.2005

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Cellular/Molecular
Stoichiometry of the 910 Nicotinic Cholinergic Receptor

Paola V. Plazas,¹ Eleonora Katz,^1,2 María E. Gomez-Casati,¹ Cecilia Bouzat,³ and A. Belén Elgoyhen¹

¹Institute of Investigations in Genetic Engineering and Molecular Biology, National Council of Scientific and Technical Investigations, and ²Department of Physiology, Molecular and Cellular Biology, Faculty of Exact and Natural Sciences, University of Buenos Aires, Buenos Aires 1428, Argentina, and ³Institute of Biochemical Investigation of Bahía Blanca, National University of the South, National Council of Scientific and Technical Investigations, Bahía Blanca F-8000FWB, Argentina

The 9 and 10 nicotinic cholinergic subunits assemble to form the receptor that mediates synaptic transmission between efferent olivocochlear fibers and hair cells of the cochlea. They are the latest vertebrate nicotinic cholinergic receptor (nAChR) subunits that have been cloned, and their identification has established a distant early divergent branch within the nAChR gene family. The 10 subunit serves as a "structural" component leading to heteromeric 910 nAChRs with distinct properties. We now have probed the stoichiometry of recombinant 910 nAChRs expressed in Xenopus oocytes. We have made use of the analysis of the population of receptors assembled from a wild-type subunit and its partner 9 or 10 subunit bearing a reporter mutation of a valine to threonine at position 13' of the second transmembrane domain (TM2). Because the mutation increased the sensitivity of the receptor for acetylcholine (ACh) but mutations at different subunits were not equivalent, the number of 9 and 10 subunits could be inferred from the number of components in compound concentration-response curves to ACh. The results were confirmed via the analysis of the effects of a mutation to threonine at position 17' of TM2. Because at this position the mutations at different subunits were equivalent, the stoichiometry was inferred directly from the shifts in the ACh EC₅₀ values. We conclude that the recombinant 910 receptor is a pentamer with a (9)₂(10)₃ stoichiometry.

Key words: nicotinic receptors; stoichiometry; ligand-gated channels; mutagenesis; cholinergic receptors; cochlea

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Received Sep 8, 2005; revised October 4, 2005; accepted October 6, 2005.

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