UNCONVENTIONAL PROPERTIES OF AN 910 NICOTINIC RECEPTOR MUTATED IN THE CHANNEL DOMAIN

PLAZAS PV; KATZ E; ELGOYHEN AB

Congreso; Society for Neuroscience 32nd Annual Meeting; 2002

Nicotinic acetylcholine receptors (nAChRs) form part of a gene superfamily, which includes g-aminobutiric acid type A, serotonin type 3 and glycine receptors. The putative channel-forming M2 domains of these receptors contain a highly conserved leucine residue that is suggested to point into the closed channel. Cloning of the a9 and a10 subunits added two peculiar members to the family of nAChRs. Recombinant expression of these subunits yields functional homomeric a9 and heteromeric a9a10 receptors that are activated by ACh but not by nicotine. It is postulated that both subunits are main components of the cochlear and vestibular cholinergic receptor. The aim of the present work was to study the function of this leucine ring in the a9a10 receptor. cDNAs for rat nicotinic a9 and a10 subunits, where the aminoacid leucine 247 was mutated to threonine, were expressed in Xenopus laevis oocytes and agonist-evoked currents were measured under two-electrode voltage-clamp. When compared to wild type receptors, ACh-evoked currents through a9a10(Leu247T) exhibited much lower desensitization kinetics and a thirty-fold increase in their apparent affinity for this agonist. Whereas choline is a weak partial agonist of the wild type receptor, it behaved as a full agonist of the mutant receptor. Furthermore, nicotine, an antagonist of the wild type receptor, elicited ionic currents when applied to this mutant. A constitutive activation of a fraction of mutant receptors was observed, even in the absence of the agonist, thus suggesting changes in the opening-closing transitions of the channels. Supported by ANPCyT and HHMI.