FUNCTIONAL PROPERTIES OF AN ALPHA9ALPHA10 NICOTINIC RECEPTOR MUTATED IN THE M2 DOMAIN.

GÓMEZ-CASATI, ME; KATZ E; WEISSTAUB, N; PLAZAS, PV; ELGOYHEN, AB

Villa Carlos Paz, Córdoba, Argentina.

Congreso; Annual Meeting of the Argentine Society for Biochemistry and Molecular Biology Research (SAIB),; 2002

SAIB

Nicotinic cholinergic receptors (nAChR) are composed of five subunits arranged in a ring around the ion permeation pathway, formed by the second transmembrane domain (M2) 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 residues contributed by each subunit and that these rings govern the pharmacological and ion transport properties of the pore. The alpha9 and alpha10 nAChR subunits are the main components of the receptor present at the outer hair cells of the cochlea. To study some structure-function relationships of the heteromeric alpha9alpha10 nAChR, we mutated the aminoacid 263 in the extracellular end of the M2 region to Thr in both subunits. Mutated subunits were co-expressed in Xenopus oocytes and agonist-evoked currents were measured under two-electrode voltage-clamp. This mutation altered the desensitization pattern of the receptor and increased the apparent affinity for ACh without affecting its calcium permeability. Choline, a weak partial agonist of the wild type alpha9alpha10 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. A constitutive activation of a fraction of the mutant receptors was observed, even in the absence of the agonist, thus suggesting changes in the opening-closing transitions of the channels.