title: Modulation of inhibitory glycine receptors in cultured embryonic mouse hippocampal neurons by zinc, thiol containing redox agents and carnosine.
abstract: Modulation of inhibitory glycine receptors by zinc (Zn(2+)) and endogenous redox agents such as glutathione may alter inhibition in the mammalian brain. Despite the abundance of Zn(2+) in the hippocampus and its ability to modulate glycine receptors, few studies have examined Zn(2+) modulation of hippocampal glycine receptors. Whether redox agents modulate hippocampal glycine receptors also remains unknown. This study examined Zn(2+) and redox modulation of glycine receptor-mediated currents in cultured embryonic mouse hippocampal neurons using whole-cell recordings. Zn(2+) concentrations below 10 microM potentiated currents elicited by low glycine, beta-alanine, and taurine concentrations by 300-400%. Zn(2+) concentrations above 300 microM produced nearly complete inhibition. Potentiating Zn(2+) concentrations shifted the dose-response curves for the three agonists to the left and decreased the Hill coefficient for glycine and beta-alanine but not taurine. Inhibiting Zn(2+) concentrations shifted the dose-response curves for glycine and beta-alanine to the right but reduced the maximum taurine response. Histidine residues may participate in potentiation because diethyl pyrocarbonate and pH 5.4 diminished Zn(2+) enhancement of glycine currents. pH 5.4 diminished Zn(2+) block of glycine currents, but diethyl pyrocarbonate did not. These findings indicate that separate sites mediate Zn(2+) potentiation and inhibition. The redox agents glutathione, dithiothreitol, tris(2-carboxyethyl)phosphine, and 5,5'-dithiobis(2-nitrobenzoic acid) did not alter glycine currents by a redox mechanism. However, glutathione and dithiothreitol interfered with the effects of Zn(2+) on glycine currents by chelating it. Carnosine had similar effects. Thus, Zn(2+) and thiol containing redox agents that chelate Zn(2+) modulate hippocampal glycine receptors with the mechanism of Zn(2+) modulation being agonist dependent.
authors.affiliation: Department of Neurology, Washington University School of Medicine, St. Louis, MO 63110, USA. thiol@neuro.wustl.edu
authors.forename: L L
authors.initials: LL
authors.lastname: Thio
authors.forename: H X
authors.initials: HX
authors.lastname: Zhang
mesh_terms: D000818:Animals; D002336:Carnosine / Q000494:pharmacology*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D004622:Embryo, Mammalian; D005998:Glycine / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D051379:Mice; D009433:Neural Inhibition / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D018408:Patch-Clamp Techniques / Q000379:methods; D018009:Receptors, Glycine / Q000378:metabolism*; D013439:Sulfhydryl Reagents / Q000494:pharmacology*; D013654:Taurine / Q000494:pharmacology; D015032:Zinc / Q000494:pharmacology*; D015091:beta-Alanine / Q000494:pharmacology
chemical_list: D018009:Receptors, Glycine; D013439:Sulfhydryl Reagents; D015091:beta-Alanine; D013654:Taurine; D002336:Carnosine; D015032:Zinc; D005998:Glycine