Characterization of the interactions of guanidine compounds with the human GABA-A ρ1 receptor

This dissertation investigates the activity of guanidine compounds GMQ, and amiloride and its derivatives on the human GABA-A ρ1 receptor, compounds classified as antagonists for the heteromeric GABA-A αβγ receptor. The GABA-A ρ receptor possesses many differences in kinetics, expression, and pharmacology from the heteromeric GABA-A αβγ receptors. Many GABA-A αβγ receptors ligands interact differently, or fail to interact with, the GABA-A ρ receptor. Thus the activity of these guanidine compounds on the GABA-A ρ1 receptor remains unknown. Based on the differential pharmacology displayed by the GABA-A ρ receptors, we propose that GMQ and amiloride would interact with the GABA-A ρ1 receptor as agonists, different from their activity on the heteromeric GABA-A αβγ receptors. Importantly, our data demonstrates GMQ and amiloride interacts with the GABA-A ρ receptors as negative and positive allosteric modulators, respectively. The 15’ residue of the second transmembrane domain of the GABA-A ρ1 receptor is important in the positive allosteric modulatory mechanism, and the accessibility of the guanidine group on the guanidine compound is integral in the positive allosteric modulation mechanisms of amiloride and its derivative 5- (N,N-Hexamethylene) amiloride (HMA). The investigation of novel compounds that interact with the GABA-A ρ receptor differently from GABA-A αβγ receptor would contribute to a better understanding of the GABA-A ρ receptor structure and the production of novel therapeutics specific for the GABA-A ρ receptor. Particularly, the GABA-A ρ receptor is implicated in retinal hypoxic disorders such as diabetic retinopathy. These guanidine compounds could be utilized as a back-bone for the production of compounds that could alleviate the pathologies caused by advanced stages of diabetic retinopathy.