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SPECIAL COMMUNICATION
1Department of Medicine, University of Cincinnati, Cincinnati 45267; 2Veterans Affairs Medical Center at Cincinnati, Cincinnati, Ohio 45220; 3Medical Genetics, University of Helsinki, Helsinki 00014, Finland; and 4Biosciences at Novum, Karolinska Institute, Huddinge 14157, Sweden
Submitted 9 June 2003 ; accepted in final form 3 September 2003
ABSTRACT
The outer medullary collecting duct (OMCD) plays an important role in bicarbonate reabsorption and acid-base regulation. An apical V-type H+-ATPase and a basolateral
exchanger, located in intercalated cells of OMCD, mediate the bicarbonate reabsorption. Here we report the identification of a new basolateral
exchanger in OMCD intercalated cells in rat kidney. Northern hybridizations demonstrated the predominant expression of this transporter, also known as SLC26A7, in the outer medulla, with lower expression levels in the inner medulla. SLC26A7 was recognized as a
90-kDa band in the outer medulla by immunoblot analysis and was localized on the basolateral membrane of a subset of OMCD cells by immunocytochemical staining. No labeling was detected in the cortex. Double-immunofluorescence labeling with the aquaporin-2 and SLC26A7 antibodies or anion exchanger-1 and SLC26A7 antibodies identified the SLC26A7-expressing cells as
-intercalated cells. Functional studies in oocytes demonstrated that increasing the osmolality of the media (to simulate the physiological milieu in the medulla) increased the
exchanger activity mediated via SLC26A7 by about threefold (P < 0.02 vs. normal condition). We propose that SLC26A7 is a basolateral
exchanger in intercalated cells of the OMCD and may play an important role in bicarbonate reabsorption in medullary collecting duct.
anion exchanger; basolateral membrane; aquaporin-2
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