FUNCTIONAL PROPERTIES OF AN 910 NICOTINIC RECEPTOR MUTATED IN THE M2 DOMAIN

GOMEZ CASATI ME; KATZ E; WEISSTAUB N; PLAZAS PV; ELGOYHEN AB

Congreso; XXXVIII Reunion Anual de la Sociedad Argentina de Bioquimica y Biologia Molecular; 2002

Nicotinic cholinergic receptors nAChR are believed to be composed of five membrane spanning subunits arranged in a ring around the ion permeation pathway, the walls of which are formed by an a-helical segment, the M2 domain, from each subunit. Site-directed mutagenesis studies have suggested that the ion channel is organized into a series of rings of amino acids consisting of the five amino acids contributed by each subunit and that these rings govern the pharmacological and ion transport properties of the pore. The a9 and a10 nAChR subunits are the main components of the receptor present at the outer hair cells of the cochlea. In order to study some structure-function relationships of the heteromeric a9a10 nAChR, we mutated the aminoacid 263 (Met in a9 and Ileu in a10) in the extracellular end of the M2 region to Thr in both subunits. Mutated subunits were co-expressed in Xenopus laevis oocytes and agonist-evoked currents were measured under two-electrode voltage-clamp. This mutation altered the desensitization pattern of the a9a10 receptor and increased the apparent affinity for ACh without affecting its Ca++ permeability. Choline, a weak partial agonist of the wild type a9a10 nAChR behaved as a full agonist of the mutant receptor. Nicotine, an antagonist of the wild type receptor, elicited ionic currents when applied to this mutant. Serotonin, an antagonist of the wild type receptor, reduced the holding current in oocytes expressing the mutant receptor. These results suggest that this mutation might alter the open-close transitions of the channel. Supported by ANPCyT, Ramón Carrillo-Arturo Oñativia and HHMI.