title: Urinary excretion of aquaporin-2 in humans: a potential marker of collecting duct responsiveness to vasopressin.
abstract: The vasopressin-sensitive water channel (aquaporin 2; AQP-2) mediates water transport across the apical plasma membrane of the renal collecting ducts and is excreted in human urine. This study presents the hypothesis that measurements of the AQP-2 excretion rate might be used as a marker of collecting-duct responsiveness to vasopressin, and therefore could be useful in the clinical evaluation of various water-balance disorders. This study presents information about the development of an antibody to human AQP-2, and measures the urinary excretion of AQP-2 by quantitative Western analysis. A standard curve of band densities was generated by using known quantities of the modified immunizing peptide to derive the amount of AQP-2 contained in aliquots of urine. AQP-2 urinary excretion changed with short-term alterations in hydration status produced either by water loading (76% decrease, P < 0.01) or by 3% sodium chloride (760% increase, P < 0.01). Steady-state 24-h urinary excretion of AQP-2 was 43 +/- 10 nmol/24 h (or 28.5 +/- 6.9 pmol/mg creatinine), and 20 +/- 6 nmol/24 h (or 18.3 +/- 7.9 pmol/mg creatinine) in men and women, respectively. Therefore, urinary AQP-2 excretion can be quantified by using Western analysis, and may serve as a marker of collecting-duct responsiveness to vasopressin in different physiologic settings.
authors.affiliation: Developmental Endocrinology Branch, National Institute of Child Health and Human Development, Bethesda, MD, USA.
authors.forename: S
authors.initials: S
authors.lastname: Elliot
authors.forename: P
authors.initials: P
authors.lastname: Goldsmith
authors.forename: M
authors.initials: M
authors.lastname: Knepper
authors.forename: M
authors.initials: M
authors.lastname: Haughey
authors.forename: B
authors.initials: B
authors.lastname: Olson
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D000818:Animals; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D001127:Arginine Vasopressin / Q000097:blood / Q000502:physiology*; D015415:Biomarkers / Q000652:urine*; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000652:urine; D015151:Immunoblotting; D007177:Inappropriate ADH Syndrome / Q000652:urine; D007473:Ion Channels / Q000737:chemistry / Q000652:urine*; D007679:Kidney Medulla / Q000378:metabolism; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D011817:Rabbits; D012076:Renal Agents / Q000097:blood*
chemical_list: C496023:AQP2 protein, human; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D015415:Biomarkers; D007473:Ion Channels; D012076:Renal Agents; D001127:Arginine Vasopressin