Functional study of the mechanism underling redox modulation of homomeric rho1 GABAc Receptor.

CI CALERO AND DJ CALVO

Huerta Grande, Cordoba

Congreso; Primera Reunion Conjunta de Neurociencias. Sociedad Argentina de Neurociencias y Taller Argentino de Neurociencias; 2009

Sociedad Argentina de Neurociencias y Taller Argentino de Neurociencias

Redox mechanisms can regulate the activity of many neurotransmitter receptors including the cys-loop receptor family. In a previous work, we demonstrated that similarly to GABAA receptors GABAC receptors (GABAr1R) can be modulated by redox agents. The most likely target for redox modulation on GABAr1R is the characteristic cys-loop formed by extracellular sulfhydryl groups (-SH) of cys 207 and 221. To test this hypothesis we studied if the chemical manipulation of these aminoacidic residues can affect GABAr1R modulation by redox agents.  Homomeric GABAr1R were expressed in X. laevis oocytes and GABA-elicited Cl- currents recorded by two-electrode voltage clamp. The application of N-ethylmaleimide (NEM), an irreversible thiol alkylating agent that forms covalent bonds with free -SH preventing further chemical reactions with these sites, modulated GABAr1 responses both, shifting to the left D-R curves and significantly increasing the maximal values. The -SH reducing agent DTT was shown to potentiate GABAr1R responses (Calero, et al., 2008). To study if the effect described above for NEM was indeed due to modification of the cys residues, now DTT actions were examined before and after the application of NEM. This treatment prevented DTT-induced potentiation of GABAr1R responses, consistently with a participation of the mentioned –SH residues. Similar experiments were performed with other two endogenous redox agents namely ascorbic acid (Asc) and GSH, which are known to modulate GABAr1R. These agents produced similar effects on D-R curves after a pretreatment with NEM; 1) a shifted to the left and 2) none significant differences in the maximal responses obtained from NEM control conditions. Our results indicate that redox agents induce at least two types of reversible redox modifications in the GABAr1R. Partially can be explained by modification of -SH and in addition, redox sensitive/NEM insensitive residues are probably involved in the functional modulation of GABAr1R. Supported by CONICET and FONCyT.