Stoichiometry of the a9a10 nicotinic cholinergic receptor

PLAZAS PV; KATZ E; GOMEZ-CASATI M; BOUZAT C; ELGOYHEN AB

J Neuroscience

Año: 2005 vol. 25 p. 1905 - 1912

The a9 and a10 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 a10 subunit serves as a ‘structural’ component leading to heteromeric a9a10 nAChRs with distinct properties. We have now probed the stoichiometry of recombinant a9a10 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 a9 or a10 subunit bearing a reporter mutation of a valine to threonine at position 13’ of the second transmembrane domain (TM2). Since the mutation increased the sensitivity of the receptor for acetylcholine (ACh), but mutations at different subunits were not equivalent, the number of a9 and a10 subunits could be inferred from the number of components in compound concentration-response curves to ACh. The results were confirmed through the analysis of the effects of a mutation to threonine at position 17’ of TM2. Since at this position mutations at different subunits were equivalent, the stoichiometry was directly inferred from the shifts in the ACh EC50 values. We conclude that the recombinant a9a10 receptor is a pentamer with a (a9)2(a10)3 stoichiometry.