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Differential Regulation of Basolateral Cl^–/HCO₃^– Exchangers SLC26A7 and AE1 in Kidney Outer Medullary Collecting Duct

Sharon Barone^*, Hassane Amlal^*, Jie Xu^*, Minna Kujala, Juha Kere, Snezana Petrovic^*, and Manoocher Soleimani^*,

*Department of Medicine University of Cincinnati, Cincinnati, Ohio; Department of Medical Genetics, University of Helsinki, Helsinki, Finland; Biosciences at Novum, Karolinska Institute, Huddinge, Sweden; and Veterans Affair Medical Center at Cincinnati, Cincinnati, Ohio

Correspondence to Dr. Manoocher Soleimani, Division of Nephrology and Hypertension, Department of Medicine, University of Cincinnati, 231 Albert Sabin Way, MSB G259, Cincinnati, OH 45267-0585; Phone: 513-558-5463; Fax: 513-558-4309; E-mail: Manoocher.Soleimani{at}uc.edu

ABSTRACT. SLC26A7 is a recently identified Cl^–/HCO₃^– exchanger that co-localizes with AE1 on the basolateral membrane of A intercalated cells (A-IC) in outer medullary collecting duct (OMCD). The purpose of these studies was to determine whether AE1 and SLC26A7 are differentially regulated in OMCD in pathophysiologic states. Toward this end, the expression and regulation of AE1 and SLC26A7 was examined in water deprivation, a condition known to increase the osmolality of the medulla. Rats were subjected to 3 d of water deprivation while having free access to food. Northern hybridizations demonstrated that in the outer medulla, the mRNA expression of SLC26A7 increased by 300% (P < 0.01 versus control; n = 3), whereas the expression of AE1 decreased by 50% (P < 0.05 versus control, n = 3) in water-deprived rats. Immunoblot analysis studies demonstrated that in the outer medulla, SLC26A7 abundance increased by 3.5-fold (P < 0.02 versus control; n = 3), whereas the AE1 abundance decreased by 55% (P < 0.05 versus control) in water deprivation. The expression of SLC26A7 remained unchanged in the kidney cortex and stomach in water deprivation, indicating the specificity of SLC26A7 upregulation in outer medulla. In situ hybridization indicated the exclusive expression of SLC26A7 in the outer medulla and double immunofluorescence labeling confirmed the co-localization of AE1 and SLC26A7 on the basolateral membrane of A-IC cells in OMCD. It is concluded that AE1 and SLC26A7 are differentially regulated in OMCD in water deprivation. On the basis of these results and previous functional studies indicating the activation of SLC26A7 activity by high osmolality, it is proposed that SLC26A7 may play an important role in bicarbonate reabsorption and or cell volume regulation in OMCD (specifically under hypertonic conditions).

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