title: Decreased expression of aquaporin 2 in the collecting duct of mice lacking the vasopressin V1a receptor.
abstract: BACKGROUND
  Vasopressin V1a receptor null (V1aR(-/-)) mice recently showed incomplete urinary concentration due to higher urine volume during control and water diuresis (euhydration), but showed normal response during dehydration (Aoyagi et al., Am J Physiol 295: F100-7, 2008).
  
  
  METHODS
  Water balance, plasma vasopressin, plasma and urine osmolality, and aquaporin 2 (AQP2) expression in the kidney of wild-type (WT) and V1aR(-/-) mice were therefore further examined using improved methods of urine collection (urinary bladder urine).
  
  
  RESULTS
  V1aR(-/-) mice demonstrated a lower urine osmolality (3,360 ± 138 vs. 3,610 ± 47 mOsm/kgH2O) and a higher plasma osmolality (354.3 ± 1.3 vs. 342.5 ± 1.5 mOsm/kgH2O) after dehydration for 24 h compared to WT mice (P < 0.05). In contrast, the plasma vasopressin concentration was significantly (P < 0.001) higher in the V1aR(-/-) mice (48.8 ± 4.8 vs. 22.1 ± 2.4 pg/ml). On the other hand, although the AQP2 protein expression in the kidney was increased after dehydration, the basal (control) and dehydration-induced AQP2 protein levels were significantly lower in V1aR(-/-) mice compared to WT mice (by Western blotting). Staining by an anti-AQP2 antibody in the luminal membrane of the collecting ducts was increased in both V1aR(-/-) and WT mice after dehydration, but was relatively weaker in the V1aR(-/-) mice (by immunohistochemistry). Moreover, urinary excretion of AQP2 protein, an index of the luminal AQP2 expression, was significantly (P < 0.05) lower in the V1aR(-/-) mice.
  
  
  CONCLUSIONS
  V1aR signaling may be fundamentally important for the expression of AQP2 in the collecting ducts during control conditions and dehydration.
authors.affiliation: Department of Physiology, Kitasato University School of Medicine, 1-15-1 Kitasato, Minami-ku, Sagamihara, 252-0374, Japan.
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Yasuoka
authors.forename: Mizuka
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Sato
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nonoguchi
authors.forename: Akito
authors.initials: A
authors.lastname: Tanoue
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Okamoto
authors.forename: Katsumasa
authors.initials: K
authors.lastname: Kawahara
mesh_terms: D000818:Animals; D051399:Aquaporin 2 / Q000096:biosynthesis*; D001774:Blood Chemical Analysis; D015153:Blotting, Western; D003681:Dehydration / Q000235:genetics / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D007150:Immunohistochemistry; D007668:Kidney / Q000378:metabolism; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D011506:Proteins / Q000302:isolation & purification / Q000378:metabolism; D017483:Receptors, Vasopressin / Q000235:genetics* / Q000502:physiology*; D013347:Subcellular Fractions / Q000378:metabolism; D016482:Urinalysis
chemical_list: D051399:Aquaporin 2; D011506:Proteins; D017483:Receptors, Vasopressin