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TRANSPORTERS FROM HUMANS:
Transporter Information:
Name: solute carrier family 4, sodium bicarbonate cotransporter, member 4
Symbol: SLC4A4
TC: 2.A.31.2.2
Locations: 4q21
Aliases: NBC1, HNBC1, NBC2, pNBC, hhNMC
GenBank: AF007216
Swiss-Prot: Q9UP50
Accession Number: NM_003759
GDBGDB:9956213
LocusLink8671
OMIM603345
PubMed (9235899): Burnham CE, Amlal H, Wang Z, Shull GE, Soleimani M. Cloning and functional expression of a human kidney Na+:HCO3- cotransporter.J Biol Chem. 1997 Aug 1;272(31):19111-4. PMID: 9235899 [PubMed - indexed for MEDLINE]

Several modes of HCO3- transport occur in the kidney, including Na+-independent Cl/HCO3- exchange (mediated by the AE family of Cl-/HCO3- exchangers), sodium-dependent Cl-/HCO3- exchange, and Na+:HCO3- cotransport. The functional similarities between the Na+-coupled HCO3- transporters and the AE isoforms (i.e. transport of HCO3- and sensitivity to inhibition by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) suggested a strategy for cloning the other transporters based on structural similarity with the AE family. An expressed sequence tag encoding part of a protein that is related to the known anion exchangers was identified in the GenBankTM expressed sequence tag data base and used to design an oligonucleotide probe. This probe was used to screen a human kidney cDNA library. Several clones were identified, isolated, and sequenced. Two overlapping cDNA clones were spliced together to form a 7.6-kilobase cDNA that contained the entire coding region of a novel protein. Based on the deduced amino acid sequence, the cDNA encodes a protein with a Mr of 116,040. The protein has 29% identity with human brain AE3. Northern blot analysis reveals that the 7.6-kilobase mRNA is highly expressed in kidney and pancreas, with detectable levels in brain. Functional studies in transiently transfected HEK-293 cells demonstrate that the cloned transporter mediates Na+:HCO3- cotransport.

PubMed (9651366): Abuladze N, Lee I, Newman D, Hwang J, Boorer K, Pushkin A, Kurtz I. Molecular cloning, chromosomal localization, tissue distribution, andfunctional expression of the human pancreatic sodium bicarbonate cotransporter.J Biol Chem. 1998 Jul 10;273(28):17689-95. PMID: 9651366 [PubMed - indexed for MEDLINE]

We report the cloning, sequence analysis, tissue distribution, functional expression, and chromosomal localization of the human pancreatic sodium bicarbonate cotransport protein (pancreatic NBC (pNBC)). The transporter was identified by searching the human expressed sequence tag data base. An I.M.A.G.E. clone W39298 was identified, and a polymerase chain reaction probe was generated to screen a human pancreas cDNA library. pNBC encodes a 1079-residue polypeptide that differs at the N terminus from the recently cloned human sodium bicarbonate cotransporter isolated from kidney (kNBC) (Burnham, C. E., Amlal, H., Wang, Z., Shull, G. E., and Soleimani, M. (1997) J. Biol. Chem. 272, 19111-19114). Northern blot analysis using a probe specific for the N terminus of pNBC revealed an approximately 7.7-kilobase transcript expressed predominantly in pancreas, with less expression in kidney, brain, liver, prostate, colon, stomach, thyroid, and spinal chord. In contrast, a probe to the unique 5' region of kNBC detected an approximately 7.6-kilobase transcript only in the kidney. In situ hybridization studies in pancreas revealed expression in the acini and ductal cells. The gene was mapped to chromosome 4q21 using fluorescent in situ hybridization. Expression of pNBC in Xenopus laevis oocytes induced sodium bicarbonate cotransport. These data demonstrate that pNBC encodes the sodium bicarbonate cotransporter in the mammalian pancreas. pNBC is also expressed at a lower level in several other organs, whereas kNBC is expressed uniquely in kidney.