title: Ammonia affects the activity and expression of soluble and particulate GC in cultured rat astrocytes.
abstract: Neurotoxic effects of ammonia are mediated by increased accumulation of nitric oxide (NO), which combines with free radicals to form a highly toxic compound, peroxynitrite. Previous experiments in vivo and in vitro have suggested that this phenomenon engages neuron-derived NO and is coupled to changes in the accumulation of cGMP. The present study accounted for the facts that: (i) astrocytes, not neurons are the morphological target of ammonia, and (ii) both NO-dependent, soluble (sGC) and NO-independent, particulate guanylate cyclase (pGC) mediate cGMP production in the cells. Neocortical rat astrocytes were treated for 1 or 24 h with 5 mM ammonium chloride ("ammonia") and then subjected to: (i) cGMP measurement, and (ii) mRNA and/or protein expression analysis of alpha1 and beta1 subunits of sGC and two pGC forms: pGC-A and pGC-B. Treatment with ammonia for 1h increased accumulation of cGMP and sGCbeta1 mRNA expression, without producing significant changes in the protein expression. This was followed by a decrease of cGMP level at 24 h treatment, associated with a decreased expression of sGCbeta1 and sGCalpha1 mRNA and sGCbeta1 protein. Expression of pGC-A and pGC-B mRNA was elevated in ammonia-treated astrocytes after 24 h. Accordingly, increased cGMP accumulation was noted in the presence of a specific sGC inhibitor (ODQ). The results show that ammonia affects cGMP production in astrocytes, and that this may involve not only sGC but also pGC.
authors.affiliation: Department of Neurotoxicology, Medical Research Centre, Polish Academy of Sciences, 02-106 Warsaw, Pawińskiego St. 5, Poland.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Konopacka
authors.forename: Inez
authors.initials: I
authors.lastname: Freśko
authors.forename: Sylwester
authors.initials: S
authors.lastname: Piaskowski
authors.forename: Jan
authors.initials: J
authors.lastname: Albrecht
authors.forename: Magdalena
authors.initials: M
authors.lastname: Zielińska
mesh_terms: D000208:Acute Disease; D000641:Ammonia / Q000378:metabolism*; D000643:Ammonium Chloride / Q000633:toxicity; D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D006152:Cyclic GMP / Q000096:biosynthesis; D006162:Guanylate Cyclase / Q000096:biosynthesis* / Q000235:genetics; D022124:Hyperammonemia / Q000201:enzymology / Q000378:metabolism; D009474:Neurons / Q000201:enzymology / Q000378:metabolism; D021122:Protein Subunits / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D018160:Receptors, Cytoplasmic and Nuclear / Q000096:biosynthesis* / Q000235:genetics; D000071756:Soluble Guanylyl Cyclase
chemical_list: D021122:Protein Subunits; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D000643:Ammonium Chloride; D000641:Ammonia; D006162:Guanylate Cyclase; D000071756:Soluble Guanylyl Cyclase; D006152:Cyclic GMP