Flumazenil-insensitive modulation of GABAA-RHO1 receptors by benzodiazepines

ANDREA N BELTRÁN GONZÁLEZ; PABLO E POMATA; JAVIER GASULLA; DANIEL J CALVO

Huerta Grande, Córdoba

Congreso; XXVIII Congreso anual de la Sociedad Argentina de Investigaciones en Neurociencias; 2013

Sociedad Argentina de Investigaciones en Neurociencias

GABA-A receptors are ligand-gated ion-channels that mediate most of the inhibitory neurotransmission in the CNS. They can be allosterically modulated by benzodiazepines (BZ) to produce anxiolytic and sedative effects in vivo. GABA-A receptors with diverse subunit composition and arrangement arise from particular combinations of five subunits, each belonging to different classes, which impart distinctive pharmacological and electrophysiological properties to the receptor subtypes. gamma subunits are critical for the typical pharmacological potentiating effects of BZs on GABA-Aalfa,beta,gamma receptors to happen, while the retinal homomeric GABA-Arho receptors still are considered insensitive to these drugs. However, preliminary experiments from our lab suggested that this may not be the case. We expressed GABA-Arho1 receptors in Xenopus laevis oocytes and recorded, using two-electrode voltage-clamp, the GABA-evoked chloride currents in the presence or absence of diverse BZ. Diazepam, a common minor tranquilizer, significantly potentiated GABA-A rho1 receptor mediated responses. Meanwhile, the atypical anxiogenic BZ 4´-chlorodiazepam exhibited a biphasic effect depending on the GABA concentration (potentiation below 1 micromolar GABA and inhibition above that concentration). All BZ actions were dose dependent and occurred in the micromolar range; BZ effects were also easily reversible and voltage independent. Co-application of the selective antagonist flumazenil had no effect on BZ modulation.