title: Nitric Oxide Increases the Expression of Aquaporin-4 Protein in Rat Optic Nerve Astrocytes through the Cyclic Guanosine Monophosphate/Protein Kinase G Pathway.
abstract: OBJECTIVE
  Nitric oxide (NO) is associated with neuroinflammation in the central nervous system. We determined whether NO increases the expression of aquaporin-4 (AQP4) in optic nerve astrocytes of rats.
  
  
  METHODS
  Isolated astrocytes were incubated under normoxic or hypoxic conditions with or without glucose (5.5 mM). The astrocytes were also exposed to different concentrations of S-nitroso-N-acetyl-DL-penicillamine (SNAP, 1.0-100 μM), an NO donor. The expression of AQP4 was determined by Western blot analyses, and NO formation was measured by the Griess reaction. The changes in astrocytic cellular volumes were determined by flow cytometry.
  
  
  RESULTS
  Hypoxia and glucose deprivation increased AQP4 expression and NO formation. Inhibition of NO synthetase (NOS) significantly suppressed these changes. SNAP caused a significant increase in AQP4 expression, and the increase was significantly suppressed by carboxy-PTIO, a scavenger of NO. Incubation with 8-Br-cyclic guanosine monophosphate (cGMP) mimicked the effects of SNAP, while the addition of either 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ; inhibitor of soluble guanylate cyclase) or KT5823 (protein kinase G inhibitor) suppressed the SNAP-induced increase in AQP4 significantly. SNAP also caused a significant increase in astrocytic cellular volume through the AQP4 channels.
  
  
  CONCLUSIONS
  NO increased the AQP4 expression of optic nerve astrocytes through the cGMP/protein kinase G pathway and enlarged their volume.
authors.affiliation: Department of Ophthalmology, Osaka Medical College, Takatsuki, Japan.
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Oku
authors.forename: Seita
authors.initials: S
authors.lastname: Morishita
authors.forename: Taeko
authors.initials: T
authors.lastname: Horie
authors.forename: Teruyo
authors.initials: T
authors.lastname: Kida
authors.forename: Masashi
authors.initials: M
authors.lastname: Mimura
authors.forename: Masanori
authors.initials: M
authors.lastname: Fukumoto
authors.forename: Shota
authors.initials: S
authors.lastname: Kojima
authors.forename: Tsunehiko
authors.initials: T
authors.lastname: Ikeda
mesh_terms: D000818:Animals; D051401:Aquaporin 4 / Q000378:metabolism*; D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism; D015153:Blotting, Western; D015687:Cell Hypoxia / Q000502:physiology; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000378:metabolism*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D005947:Glucose / Q000494:pharmacology; D008297:Male; D009569:Nitric Oxide / Q000502:physiology*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000378:metabolism; D009900:Optic Nerve / Q000166:cytology*; D051381:Rats; D017208:Rats, Wistar; D026423:S-Nitroso-N-Acetylpenicillamine / Q000494:pharmacology; D013549:Sweetening Agents / Q000494:pharmacology
chemical_list: C496032:Aqp4 protein, rat; D051401:Aquaporin 4; D004791:Enzyme Inhibitors; D020030:Nitric Oxide Donors; D013549:Sweetening Agents; D009569:Nitric Oxide; D026423:S-Nitroso-N-Acetylpenicillamine; D019001:Nitric Oxide Synthase; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP; D005947:Glucose