title: NBCn1 is a basolateral Na+-HCO3- cotransporter in rat kidney inner medullary collecting ducts.
abstract: 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.
authors.affiliation: The Water and Salt Research Ctr., University of Aarhus, Wilhelm Meyers Allé Bldg. 233, 8000 Aarhus C, Denmark. jp@ana.au.dk
authors.forename: Jeppe
authors.initials: J
authors.lastname: Praetorius
authors.forename: Young-Hee
authors.initials: YH
authors.lastname: Kim
authors.forename: Elena V
authors.initials: EV
authors.lastname: Bouzinova
authors.forename: Sebastian
authors.initials: S
authors.lastname: Frische
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Rojek
authors.forename: Christian
authors.initials: C
authors.lastname: Aalkjaer
authors.forename: Søren
authors.initials: S
authors.lastname: Nielsen
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000136:Acid-Base Equilibrium / Q000502:physiology*; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D004232:Diuretics / Q000494:pharmacology; D005665:Furosemide / Q000494:pharmacology; D015870:Gene Expression; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D007150:Immunohistochemistry; D007679:Kidney Medulla / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008297:Male; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017693:Sodium Bicarbonate / Q000493:pharmacokinetics; D027982:Sodium-Bicarbonate Symporters / Q000235:genetics* / Q000378:metabolism*
chemical_list: D004232:Diuretics; D012333:RNA, Messenger; C422004:Slc4a4 protein, rat; D027982:Sodium-Bicarbonate Symporters; D000643:Ammonium Chloride; D005665:Furosemide; D017693:Sodium Bicarbonate; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid