title: Rat renal arcade segment expresses vasopressin-regulated water channel and vasopressin V2 receptor.
abstract: The arcades are long, branched renal tubules which connect deep and mid-cortical nephrons to cortical collecting ducts in the renal cortex. Because they are inaccessible by standard physiological techniques, their functions are poorly understood. In this paper, we demonstrate that the arcades are a site of expression of two proteins, aquaporin-2 (the vasopressin-regulated water channel) and the V2 vasopressin receptor, that are important to regulated water transport in the kidney. Using a peptide-derived polyclonal antibody to aquaporin-2, quantitative ELISA in microdissected segments showed that aquaporin-2 is highly expressed in arcades and that the expression is increased in response to restriction of fluid intake. Immunocytochemistry revealed abundant aquaporin-2 labeling of structures in the cortical labyrinth in a pattern similar to that of the Na(+)-Ca2+ exchanger and kallikrein, marker proteins expressed in arcades but not in cortical collecting ducts. RT-PCR experiments demonstrated substantial aquaporin-2 and V2 receptor mRNA in microdissected arcades. In situ hybridization, using 35S-labeled antisense cRNA probes for the V2 receptor demonstrated strong labeling of both arcades and cortical collecting ducts. Thus, these results indicate that the arcades contain the specific proteins associated with vasopressin-regulated water transport, and may be a heretofore unrecognized site of free water absorption.
authors.affiliation: Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: B K
authors.initials: BK
authors.lastname: Kishore
authors.forename: B
authors.initials: B
authors.lastname: Mandon
authors.forename: N B
authors.initials: NB
authors.lastname: Oza
authors.forename: S R
authors.initials: SR
authors.lastname: DiGiovanni
authors.forename: R A
authors.initials: RA
authors.lastname: Coleman
authors.forename: N L
authors.initials: NL
authors.lastname: Ostrowski
authors.forename: J B
authors.initials: JB
authors.lastname: Wade
authors.forename: M A
authors.initials: MA
authors.lastname: Knepper
mesh_terms: D000818:Animals; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D001483:Base Sequence; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007473:Ion Channels / Q000032:analysis* / Q000235:genetics; D007671:Kidney Concentrating Ability; D007684:Kidney Tubules / Q000737:chemistry*; D008297:Male; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D017483:Receptors, Vasopressin / Q000032:analysis* / Q000235:genetics
chemical_list: C496025:Aqp2 protein, rat; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D007473:Ion Channels; D012333:RNA, Messenger; D017483:Receptors, Vasopressin