title: Ammonia inhibits the C-type natriuretic peptide-dependent cyclic GMP synthesis and calcium accumulation in a rat brain endothelial cell line.
abstract: Recently we reported a decrease of C-type natriuretic peptide (CNP)-dependent, natriuretic peptide receptor 2 (NPR2)-mediated cyclic GMP (cGMP) synthesis in a non-neuronal compartment of cerebral cortical slices of hyperammonemic rats [Zielińska, M., Fresko, I., Konopacka, A., Felipo, V., Albrecht, J., 2007. Hyperammonemia inhibits the natriuretic peptide receptor 2 (NPR2)-mediated cyclic GMP synthesis in the astrocytic compartment of rat cerebral cortex slices. Neurotoxicology 28, 1260-1263]. Here we accounted for the possible involvement of cerebral capillary endothelial cells in this response by measuring the effect of ammonia on the CNP-mediated cGMP formation and intracellular calcium ([Ca2+]i) accumulation in a rat cerebral endothelial cell line (RBE-4). We first established that stimulation of cGMP synthesis in RBE-4 cells was coupled to protein kinase G (PKG)-mediated Ca2+ influx from the medium which was inhibited by an L-type channel blocker nimodipine. Ammonia treatment (1h, 5mM NH4Cl) evoked a substantial decrease of CNP-stimulated cGMP synthesis which was related to a decreased binding of CNP to NPR2 receptors, and depressed the CNP-dependent [Ca2+]i accumulation in these cells. Ammonia also abolished the CNP-dependent Ca2+ accumulation in the absence of Na+. In cells incubated with ammonia in the absence of Ca2+ a slight CNP-dependent increase of [Ca2+]i was observed, most likely representing Ca2+ release from intracellular stores. Depression of CNP-dependent cGMP-mediated [Ca2+]i accumulation may contribute to cerebral vascular endothelial dysfunction associated with hyperammonemia or hepatic encephalopathy.
authors.affiliation: Department of Neurotoxicology, Medical Research Centre, Polish Academy of Sciences, Pawińskiego 5, 02-106 Warsaw, Poland.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Konopacka
authors.forename: Magdalena
authors.initials: M
authors.lastname: Zielińska
authors.forename: Jan
authors.initials: J
authors.lastname: Albrecht
mesh_terms: D000641:Ammonia / Q000378:metabolism* / Q000633:toxicity; D000814:Aniline Compounds; D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002536:Cerebral Arteries / Q000378:metabolism* / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000187:drug effects / Q000502:physiology; D006152:Cyclic GMP / Q000096:biosynthesis*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D006501:Hepatic Encephalopathy / Q000378:metabolism / Q000503:physiopathology; D022124:Hyperammonemia / Q000378:metabolism / Q000503:physiopathology; D020098:Natriuretic Peptide, C-Type / Q000187:drug effects / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017461:Receptors, Atrial Natriuretic Factor / Q000187:drug effects / Q000378:metabolism; D014966:Xanthenes; D000099242:Atrial Natriuretic Factor Receptor B
chemical_list: D000641:Ammonia; D000814:Aniline Compounds; D002118:Calcium; D002121:Calcium Channel Blockers; D006152:Cyclic GMP; D017869:Cyclic GMP-Dependent Protein Kinases; D020098:Natriuretic Peptide, C-Type; D017461:Receptors, Atrial Natriuretic Factor; D014966:Xanthenes; D000099242:Atrial Natriuretic Factor Receptor B; C059715:Fluo-3