title: Expression cloning and characterization of a renal electrogenic Na+/HCO3- cotransporter.
abstract: Bicarbonate transporters are the principal regulators of pH in animal cells, and play a vital role in acid-base movement in the stomach, pancreas, intestine, kidney, reproductive system and central nervous system. The functional family of HCO3- transporters includes Cl- -HCO3- exchangers, three Na+/HCO3- cotransporters, a K+/HCO3- cotransporter, and a Na+-driven Cl- -HCO3- exchanger. Molecular information is sparse on HCO3- transporters, apart from Cl- -HCO3- exchangers ('anion exchangers'), whose complementary DNAs were cloned several years ago. Attempts to clone other HCO3- transporters, based on binding of inhibitors, protein purification or homology with anion exchangers, have so far been unsuccessful. Here we monitor the intracellular pH and membrane voltage in Xenopus oocytes to follow the expression of the most electrogenic transporter known: the renal 1:3 electrogenic Na+/HCO3- cotransporter from the salamander Ambystoma tigrinum. We now report the successful cloning and characterization of a cDNA encoding a cation-coupled HCO3- transporter. The encoded protein is 1,035 amino acids long with several potential membrane-spanning domains. We show that when it is expressed in Xenopus oocytes, this protein is electrogenic, Na+ and HCO3- dependent, and blocked by the anion-transport inhibitor DIDS, and conclude that it is the renal electrogenic sodium bicarbonate cotransporter (NBC).
authors.affiliation: Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA. mromero@biomed.med.yale.edu
authors.forename: M F
authors.initials: MF
authors.lastname: Romero
authors.forename: M A
authors.initials: MA
authors.lastname: Hediger
authors.forename: E L
authors.initials: EL
authors.lastname: Boulpaep
authors.forename: W F
authors.initials: WF
authors.lastname: Boron
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000557:Ambystoma; D000595:Amino Acid Sequence; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D003001:Cloning, Molecular; D004594:Electrophysiology; D015870:Gene Expression; D007668:Kidney / Q000378:metabolism*; D008969:Molecular Sequence Data; D009865:Oocytes; D012964:Sodium / Q000378:metabolism*; D027982:Sodium-Bicarbonate Symporters; D014982:Xenopus laevis
chemical_list: D001639:Bicarbonates; D002352:Carrier Proteins; D027982:Sodium-Bicarbonate Symporters; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid