Mouse Na+: HCO3- cotransporter isoform NBC-3 (kNBC-3): cloning, expression, and renal distribution.
BACKGROUND
Na+:HCO3- cotransporters mediate the transport of HCO3- into or out of the cell. We recently reported the partial cloning and characterization of a new human Na+:HCO3- cotransporter (referred to as NBC-3 or kNBC-3). The purpose of the present studies was to clone the mouse kNBC-3 and to examine its properties and expression in the kidney.


METHODS
Using primers from human kNBC-3 cDNA and 5' and 3' rapid amplification cDNA end polymerase chain reaction (RACE PCR), the mouse kNBC-3 full-length cDNA was cloned from inner medullary collecting duct (mIMCD-3) cells. The tissue distribution and functional properties of NBC-3 was determined using established methods.


RESULTS
The coding region of the mouse kNBC-3 has 1089 amino acids and shows 73 and 56% identity to human NBC-2 and NBC-1, respectively. The renal distribution of kNBC-3 demonstrated a unique expression pattern: Whereas kNBC-1 is predominantly expressed in the cortex and is absent in the inner medulla, kNBC-3 shows an intense expression level in the inner medulla and is absent in the cortex. Expression studies in oocytes indicated that NBC-3 mediates Na-dependent HCO3- cotransport. Electrophysiological experiments demonstrated that unlike kNBC-1, which is electrogenic, kNBC-3 is electroneutral.


CONCLUSIONS
Based on its distribution and electroneutrality, we propose that kNBC-3 mediates the transport of HCO3- into the cells.
Division of Nephrology, Department of Internal Medicine, University of Cincinnati, and the Veterans Affairs Medical Center, Cincinnati, Ohio, USA.
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Z
Wang
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Conforti
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Petrovic
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Amlal
C E
CE
Burnham
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M
Soleimani
D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001483:Base Sequence / Q000235:genetics; D001921:Brain / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D005260:Female; D015870:Gene Expression; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D027982:Sodium-Bicarbonate Symporters; D014018:Tissue Distribution; D014981:Xenopus
D002352:Carrier Proteins; D018076:DNA, Complementary; D027982:Sodium-Bicarbonate Symporters