Browsing by Subject "guanidine"
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Item Characterization of the interactions of guanidine compounds with the human GABA-A ρ1 receptor(2015-12-01) Snell, Heather D.; Gonzales, Eric B.; Dillon, Glenn H.; Singh, MeharvanThis 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.Item NOVEL GABAA-RHO1 INTERACTIONS WITH ACID SENSING ION CHANNEL LIGANDS(2014-03) Snell, Heather D.; Gonzales, Eric B.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.