Histidine 141 is critical for GABArho1 receptor sensitivity to ascorbic acid

CALERO CI; CALVO DJ

Huerta Grande

Congreso; Segunda Reunion Conjunta de Neurociencia (IIRCN); 2010

Sociedad Argentina de Neurociencia y Taller Argentino de Neurociencia

Neurotransmitter receptors, including ionotropic GABA receptors, can be regulated by redox mechanisms. We demonstrated that homomeric rho1 GABAC receptors (GABA ρ1R) are modulated by ascorbic acid (Asc) and other redox agents (Calero and Calvo, 2008). Asc modulation was partially explained by a chemical modification of the SH-groups at two extracellular cysteines forming the cys-loop (C177 and C191) of GABA ρ1R. However, we also showed an additional allosteric mechanism involved. Histidine 141 (H141) is essential for allosteric effects induced by Zn2+ on GABA ρ1R. In order to determine if this aminoacidic residue also participates in the mechanism of Asc modulation, we used site-directed mutagenesis. Wild type and mutant receptors were expressed in X. laevis oocytes and GABA-evoked Cl- currents electrophysiologically recorded. Maximal responses mediated by H141D GABA ρ1R were significantly potentiated by 3 mM Asc, as observed for wt GABA ρ1R. However, Asc was unable to produce shifts in the EC50 of D-R curves of receptors carrying the mutation. Our results suggest that H141 is involved in the allosteric effects evoked by Asc on GABA ρ1R.