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https://bar.utoronto.ca/thalemine/service/ is incorrect| Description | Bicarbonate (HCO 3-) transport mechanisms are the principal regulators of pH in animal cells. Such transport also plays a vital role in acid-base movements in the stomach, pancreas, intestine, kidney, reproductive organs and the central nervous system. Functional studies have suggested four different HCO 3-transport modes. Anion exchanger proteins exchange HCO 3-for Cl -in a reversible, electroneutral manner [ ]. Na+/HCO 3-co-transport proteins mediate the coupled movement of Na +and HCO 3-across plasma membranes, often in an electrogenic manner [ ]. Na+driven Cl -/HCO 3-exchange and K +/HCO 3-exchange activities have also been detected in certain cell types, although the molecular identities of the proteins responsible remain to be determined. Sequence analysis of the two families of HCO 3-transporters that have been cloned to date (the anion exchangers and Na +/HCO 3-co-transporters) reveals that they are homologous. This is not entirely unexpected, given that they both transport HCO 3-and are inhibited by a class of pharmacological agents called disulphonic stilbenes [ ]. They share around ~25-30% sequence identity, which is distributed along their entire sequence length, and have similar predicted membrane topologies, suggesting they have ~10 transmembrane (TM) domains.Na +/HCO 3-co-transport proteins are involved in cellular HCO 3-absorption and secretion, and also with intracellular pH regulation. They mediate the coupled movement of Na +and HCO 3-across plasma membranes in most of the cell types so far investigated. A single HCO 3-is transported together with one to three Na +; this transport mode is therefore often electrogenic. In the kidney, an electrogenic Na +/HCO 3-co-transporter is the principal HCO 3-transporter of the renal proximal tubule, and is responsible for reabsorption of more than 85% of the filtered load of HCO 3-[ ]. Until recently, the molecular nature of these Na+/HCO 3-co-transporters had remained undiscovered, as initial attempts to clone them based on presumed homology to Cl -/HCO 3-(anion) exchangers had proved unsuccessful. Instead, an expression cloning strategy was successfully utilised to identify the Na +/HCO 3-co-transporter from salamander kidney, an organ previously found to possess electrogenic Na +/HCO 3-co-transport activity [ ]. At least 3 mammalian Na+/HCO 3-co-transporters have since been cloned, with similar primary sequence lengths and putative membrance topologies. One of these has been found to be a kidney-specific isoform [ ], which is near-identical (except for a varying N-terminal region) to a more widely-distributed co-transporter cloned from pancreatic tissue []. | Name | Sodium bicarbonate cotransporter |
| Short Name | Na/HCO3_transpt | Type | Family |
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