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

PLAZAS PV; KATZ E; ELGOYHEN AB

Congreso; xIV International Biophysics congress; 2002

Nicotinic acetylcholine receptors (nAChRs) form part of a gene superfamily, which includes g-aminobutiric acid type A, serotonine type 3 and glycine receptors. The putative channel-forming MII 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 the a9 and a10 nAChRs 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. We studied the function of this leucine ring in the a9a10 receptor. cDNAs for rat nicotinic a9 and a10 subunits where the amino acid Leu247 was mutated to threonine were expressed in Xenopus oocytes. When compared to WT receptors, ACh-evoked currents through a9a10(Leu247T) exhibited low desensitization kinetics and a high apparent affinity for this agonist. Furthermore, nicotine, an antagonist of the WT 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.