STRUCTURE-FUNCTION RELATIONSHIP OF THE 910 NICOTINIC RECEPTOR

P.V. PLAZAS; M. VERBITSKY; A.B. ELGOYHEN

Congreso; XVIII Reunión Anual de la Sociedad Argentina de Neuroquímica; 2000

Recombinant expression of the a9 and a10 nicotinic acetylcholine receptor (nAchR) subunits yields functional homomeric a9 and heteromeric a9a10 receptors. It is postulated that both subunits are main components of the outer hair cells´ cholinergic receptor. The activation of this receptor is a pathway for Ca2+ entry for the subsequent activation of a K+ conductance that leads to hyperpolarization. The a9a10 heteromer differs from the a9 homomer in: its desensitization pattern, its Ca2+ sensitivity and its current-voltage relationship. The aim of this work was to study the structural determinants responsible for these differences. We generated the following mutants: a9(Q261M)a10, a9a10(Q261M), a9a10(Q261R) and a9a10(D242A). Q261 is present in the transmembrane region II (TMII), and D242 forms the citoplasmic ring of negatively charged amino acids, located between TMI and TMII. When expressed in Xenopus laevis oocytes, the heteromer a9(Q261M)a10 yields a receptor less sensitive to Ca2+ blockage than a9a10(Q261M) and a9a10; the heteromer a9a10(Q261R) differs from a9a10 in its Ca2+ permeability and its desensitization pattern. The position corresponding to the citoplasmic ring of negatively charged amino acids is occupied by alanine (A) in a9 and by aspartic acid (D) in a10. The receptor a9a10(D242A) displays a current-voltage relationship that resembles that reported for the a9 homomer. These results suggest that residues within and adjacent to the TMII of a9a10 are determinants of ionic selectivity and blockage by divalent ions.   Supported by ANPCyT and Howard Huges Medical Institute.