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1Department of Medicine, University of Cincinnati School of Medicine, and 3Research Services, Veterans Affairs Medical Center, Cincinnati, Ohio; and 2Department of Medical Genetics and Division of Renal Medicine, University of Cambridge, Cambridge, United Kingdom
Submitted 13 June 2005 ; accepted in final form 7 December 2005
SLC26A7 is a newly identified basolateral Cl/HCO3 exchanger specific to
-intercalated cells of the outer medullary collecting duct (OMCD). The purpose of the present experiments was to examine the expression of SLC26A7 in kidneys of vasopressin-deficient Brattleboro rats before and after treatment with desamino-Cys1,D-Arg8-vasopressin (dDAVP). Brattleboro rats were treated with dDAVP, a vasopressin analog, for 8 days, and their kidneys were examined for the expression of SLC26A7. The expression of SLC26A7 protein, as examined by immunofluorescence, was undetectable in kidneys of Brattleboro rats. However, treatment with dDAVP induced expression of SLC26A7 protein, restoring it to levels observed in normal rats. These results were verified by Western blot analysis. The mRNA expression of SLC26A7 remained unchanged in response to dDAVP. Immunofluorescent labeling demonstrated abundant levels of anion exchanger type 1 in the OMCD of Brattleboro rats and a mild reduction in response to dDAVP. The abundance of H+-ATPase was not affected by dDAVP. The increased SLC26A7 expression directly correlated with enhanced aquaporin-2 expression, which is proportional to increased interstitial osmolarity in the medulla. In conclusion, vasopressin increases the expression of SLC26A7 protein through posttranscriptional mechanisms in the OMCD. The induction of SLC26A7 by vasopressin in OMCD cells of Brattleboro rats is likely an attempt by cells to regulate their cell volume and maintain HCO3 absorption in a state associated with increased interstitial medullary tonicity.
medullary osmolarity; diabetes insipidus; bicarbonate absorption
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