title: Transient hyperosmolality modulates expression of cardiac aquaporins.
abstract: OBJECTIVE
  Hyperosmolarity is a common complication in intensive care patients, dysregulating water balance in many organs including brain and heart. The aquaporin (AQP) water channels, in particular AQP1 and -4, have been suggested to play an important role in fluid homeostasis of the myocardium. In many organs AQP expression is regulated by osmolarity, drastically altering water permeability of the cell membranes. The aim of our study was to investigate if plasma hyperosmolality may regulate cardiac expression of AQP1 and -4, and if so, at which magnitude and time frame such regulation takes place.
  
  
  METHODS
  C57Bl6 mice were injected intraperitoneally with either 1.5 ml 0.154 Mol (isoosmotic), 0.5 ml 1 Mol (mild hyperosmotic) or 0.5 ml 2 Mol (strong hyperosmotic) NaCl. Plasma, hearts, and forebrains were harvested before injection ("time 0"), and after 1, 4, 8 and 24 h. AQP1 and -4 expression were analyzed using qPCR and Western blot.
  
  
  RESULTS
  Isoosmotic and mild hyperosmotic injections caused no important changes in cardiac AQP expression. Strong hyperosmotic NaCl injections induced an upregulation of AQP1 mRNA and glycosylated fraction of AQP1 protein in the heart without changes of the total protein. AQP4 mRNA and protein decreased in the heart and increased in the brain after hyperosmotic NaCl. The change in AQP4 protein content in the brain preceded the increase of mRNA.
  
  
  CONCLUSIONS
  As in the brain, expression of AQP1 and -4 in the heart is influenced by changes in plasma osmolality. Changes in AQP expression may alter cardiac function in hyperosmotic states.
authors: Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, Postboks 1103 Blindern, 0317 Oslo, Norway. arkady.rutkovskiy@medisin.uio.no
authors: Arkady
authors: A
authors: Rutkovskiy
authors: Lars Henrik
authors: LH
authors: Mariero
authors: Ståle
authors: S
authors: Nygård
authors: Kåre-Olav
authors: KO
authors: Stensløkken
authors: Guro
authors: G
authors: Valen
authors: Jarle
authors: J
authors: Vaage
mesh_terms: D000818:Animals; D051398:Aquaporin 1 / Q000096:biosynthesis*; D051401:Aquaporin 4 / Q000096:biosynthesis*; D001921:Brain / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009206:Myocardium / Q000378:metabolism*; D009994:Osmolar Concentration; D010949:Plasma / Q000502:physiology*
chemical_list: C496021:Aqp1 protein, mouse; C496031:Aqp4 protein, mouse; D051401:Aquaporin 4; D051398:Aquaporin 1