title: Astroglial NMDA receptors inhibit expression of Kir4.1 channels in glutamate-overexposed astrocytes in vitro and in the brain of rats with acute liver failure.
abstract: Astroglial inward rectifying Kir4.1 potassium channels are fundamental for the maintenance of ion and water homeostasis in the central nervous system (CNS). Down-regulation of Kir4.1 expression is observed in CNS disorders associated with excessive extracellular glutamate (Glu) accumulation, including hepatic encephalopathy related to acute liver failure (ALF). Here we demonstrate that prolonged (3 days) treatment of cultured rat cortical astrocytes with 2 mM Glu or 100 µM NMDA decreases the expression of Kir4.1 mRNA and protein. Inhibition by Glu of Kir4.1 mRNA expression was reversed by NMDA receptor antagonists MK-801 and AP-5 (each at 50 µM), and by a non-transportable inhibitor of Glu uptake TBOA (100 µM). MK-801 reversed the inhibitory effect of Glu on Kir4.1 protein expression. In contrast, transcription of Kir4.1 channels was not affected by: (i) a transportable Glu uptake inhibitor PDC (100 µM); (ii) by group I mGluR antagonist MTEP (100 µM); (iii) by antagonists of oxidative-nitrosative stress (ONS) in astrocytes, including the neuroprotective amino acid taurine (Tau; 10 mM), the NADPH oxidase inhibitor apocyanine (APO; 300 µM), the nitric oxide synthase inhibitor, L-NNA (100 µM), and a membrane permeable glutathione precursor, glutathione-diethyl ester (GEE; 3 mM). Down-regulation of Kir4.1 transcription in rats with ALF was attenuated by intraperitoneal administration of a competitive NMDA receptor antagonist memantine, but not by histidine, which reverses ONS associated with ALF. Collectively, the results indicate that over-activation of astroglial NMDA receptors, aided by as yet undefined effects of Glu entry to astrocytes, is a primary cause of the reduction of Kir4.1 expression in CNS disorders associated with increased exposure to Glu.
authors.affiliation: Department of Neurotoxicology, Mossakowski Medical Research Centre, Polish Academy of Science, Warsaw, Poland.
authors.forename: Marta
authors.initials: M
authors.lastname: Obara-Michlewska
authors.affiliation: Department of Neurotoxicology, Mossakowski Medical Research Centre, Polish Academy of Science, Warsaw, Poland.
authors.forename: Joanna
authors.initials: J
authors.lastname: Ruszkiewicz
authors.affiliation: Department of Neurotoxicology, Mossakowski Medical Research Centre, Polish Academy of Science, Warsaw, Poland.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Zielińska
authors.affiliation: Department of Neurotoxicology, Mossakowski Medical Research Centre, Polish Academy of Science, Warsaw, Poland; Faculty of Life Sciences, University of Manchester, Manchester, UK.
authors.forename: Alexei
authors.initials: A
authors.lastname: Verkhratsky
authors.affiliation: Department of Neurotoxicology, Mossakowski Medical Research Centre, Polish Academy of Science, Warsaw, Poland. Electronic address: jalbrecht@imdik.pan.pl.
authors.forename: Jan
authors.initials: J
authors.lastname: Albrecht
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D018698:Glutamic Acid / Q000633:toxicity*; D017114:Liver Failure, Acute / Q000235:genetics / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D000098854:Kcnj10 Channel
chemical_list: D000098854:Kcnj10 Channel; D024661:Potassium Channels, Inwardly Rectifying; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid
keywords: Astrocytic NMDA receptors; Excitotoxicity; Glutamate; Hepatic encephalopathy; K(ir)4.1; Oxidative/nitrosative stress