NOVEL GABAA-RHO1 INTERACTIONS WITH ACID SENSING ION CHANNEL LIGANDS

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 located in the retina. A group of ligands, which possess a guanidine group, have been shown to influence classical GABAA receptors. Many, however, have not yet been tried on the GABAA-rho receptor subclass. Our experiments show that these compounds have contrasting effects on the GABAA-rho1 receptor, which could lead to a novel binding site, and explain many side effects of certain drugs containing the guanidine group. Purpose (a): 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. GABAA-rho exhibits unique properties, such as insensitivity to select antagonists of the heteromeric GABAA receptors. 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. Methods (b): The human GABAA-rho1 receptors were expressed in HEK-293T cells, and activity was analyzed using whole cell patch-clamp electrophysiology. Results (c): 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,while a different ligand with the same guandine group, shifted the GABA EC50 to lower GABA concentrations. When applied alone, it failed to directly activate GABAA-rho1 receptors. Conclusions (d): 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 GABAA-rho receptors and offer a novel chemical structure to design novel GABAA-rho therapeutics.