NBCn1 is a basolateral Na+-HCO3- cotransporter in rat kidney inner medullary collecting ducts

Primary cultures of rat inner medullary collecting duct (IMCD) cells Na(+) dependently import HCO(3)(-) across the basolateral membrane through an undefined transport protein. We used RT-PCR, immunoblotting, and immunohistochemistry to identify candidate proteins for this basolateral Na(+)-HCO(3)(-)...

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Bibliographic Details
Published in:American journal of physiology. Renal physiology 2004-05, Vol.286 (5), p.F903-F912
Main Authors: Praetorius, Jeppe, Kim, Young-Hee, Bouzinova, Elena V, Frische, Sebastian, Rojek, Aleksandra, Aalkjaer, Christian, Nielsen, Søren
Format: Article
Language:English
Subjects:
4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid - pharmacology
Acid-Base Equilibrium - physiology
Ammonium Chloride - pharmacology
Animals
Biological Transport - drug effects
Biological Transport - physiology
Diuretics - pharmacology
Furosemide - pharmacology
Gene Expression
Hydrogen-Ion Concentration
Immunoblotting
Immunohistochemistry
Kidney Medulla - metabolism
Kidney Tubules, Collecting - metabolism
Male
Rats
Rats, Wistar
Reverse Transcriptase Polymerase Chain Reaction
RNA, Messenger - analysis
Sodium Bicarbonate - pharmacokinetics
Sodium-Bicarbonate Symporters - genetics
Sodium-Bicarbonate Symporters - metabolism
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Summary:Primary cultures of rat inner medullary collecting duct (IMCD) cells Na(+) dependently import HCO(3)(-) across the basolateral membrane through an undefined transport protein. We used RT-PCR, immunoblotting, and immunohistochemistry to identify candidate proteins for this basolateral Na(+)-HCO(3)(-) cotransport. The mRNA encoding the electroneutral Na(+)-HCO(3)(-) cotransporter NBCn1 was detected as the only Na(+)-HCO(3)(-) cotransporter in the rat inner medulla (IM) among the five characterized Na(+)-dependent HCO(3)(-) transporters. The mRNA of a yet uncharacterized transporter-like protein, BTR1, was also present in the IM, but its expression in microdissected tubules seemed restricted to the thin limbs of Henle's loop. Immunoblotting confirmed the presence of NBCn1 as an approximately 180-kDa protein of the rat IM. Anti-NBCn1 immunolabeling was confined to the basolateral plasma membrane domain of IMCD cells in the papillary two-thirds of the IM. Consistent with the presence of NBCn1, IMCD cells possessed stilbene-insensitive, Na(+)- and HCO(3)(-)-dependent pH recovery after acidification, as assessed by fluorescence microscopy using a pH-sensitive intracellular dye. In furosemide-induced alkalotic rats, NBCn1 protein abundance was decreased in both the IM and inner stripe of outer medulla (ISOM) as determined by immunoblotting and immunohistochemistry. In contrast, NBCn1 abundance in the IM and ISOM was unchanged in NaHCO(3)-loaded animals, and the NBCn1 abundance increased only in the ISOM after NH(4)Cl loading. In conclusion, NBCn1 is a basolateral Na(+)-HCO(3)(-) cotransporter of IMCD cells and is differentially regulated in IMCD and medullary thick ascending limb.
ISSN:1931-857X
1522-1466
DOI:10.1152/ajprenal.00437.2002