Novel GABAA‐rho1 interactions with acid sensing ion channel ligands (1059.3)

Abstract

γ‐ amino butyric acid (GABA) is the major inhibitory neurotransmitter in the vertebrate brain, and targets the ionotropic GABAA receptors. GABAC, or GABAA‐rho, is a subclass of GABAA receptors composed entirely of rho (ρ) subunits and are located on the axonal terminal of retinal bipolar cells, where it not only exhibits a tonic inhibitory current, but also regulates the GABA‐A and other GABAA‐rho synaptic currents (Jones et al 2011). GABAA‐rho exhibits unique properties, such as insensitivity to select antagonists of the heteromeric GABAA receptors (Korpi et al., 2002). A group of ligands, which possess a guanidine group, have been shown to influence GABAA receptors. These compounds, such as (S)‐2‐Guanidinopropionic acid and guanidine acetic acid were competitive antagonists for the GABAA‐rho1 receptor. Other guanidine compounds that are acid sensing ion channel (ASIC) ligands, might also exhibit unique effects on the GABAA‐rho1 receptor. We hypothesize that these ASIC ligands will exhibit unique intrinsic activities on the GABAA‐rho1 receptor, which is different from that of the heteromeric GABAA receptor. The human GABAA‐rho1 receptors were expressed in HEK‐293T cells, and activity was analyzed using whole cell patch‐clamp electrophysiology. When co‐applied with GABA and compared to the GABA concentration profile, one ligand was found to decrease the maximal response, with no change in the GABA EC50. This indicates characteristics of non‐competitive inhibition, while a different ligand shifted the GABA EC50 to lower GABA concentrations, suggesting this guanidine compound is a positive allosteric modulator. When applied alone, it failed to directly activate GABA rho1 receptors. These contrasting effects suggest that these ligands act at two binding sites within the GABAA‐rho architecture. Future experiments will focus on additional characterization of these novel effects on GABA rho receptors and offer a novel chemical structure to design novel GABAA‐rho therapeutics.Grant Funding Source: Supported by: Welch Foundation Grant No: BK‐1736, NIH training grant: NBA T32 AG020494