Na+-coupled HCO3- cotransport Authored: Jassal, B, 2009-06-04 Edited: Jassal, B, 2009-06-04 Pubmed10347222 Pubmed10362779 Pubmed10545938 Pubmed10978526 Pubmed11305939 Pubmed11788353 Pubmed9235899 Pubmed9651366 Reactome Database ID Release 43425483 Reactome, http://www.reactome.org ReactomeREACT_19247 Reviewed: He, L, 2009-08-24 Some members of the SLC4A family couple the transport of bicarbonate (HCO3-) to the movement of sodium ions (Na+), they being members 4, 5, 7 and 9. SLC4A4 (NBCe1) is an electrogenic sodium/bicarbonate cotransporter with a Na+:HCO3- stoichiometry of 1:3, although it can also be 1:2 (Burnham CE et al, 1997). SLC4A4 encodes a protein which is expressed in the kidney and pancreas, with lesser expression in many other tissues (Abuladze N et al, 1998). Mutations in SLC4A4 cause permanent isolated proximal renal tubular acidosis (pRTA) (results in accumulation of acid in the body due to a failure of the kidneys to effectively acidify urine) with ocular abnormalities (Igarashi T et al, 1999).<br><br>SLC4A5 encodes a protein which is expressed in liver, spleen and testes, with lower levels expressed in parts of the brain and kidney (Sassani P et al, 2002). It may have a housekeeping function in regulating the pH of these tissues (Pushkin A et al, 2000). SLC4A7 (NBC3, NBCn1) encodes a protein which performs electroneutral cotransport of Na+ and HCO3- with a 1:1 stoichiometry. It is highly expressed in testes and spleen and, to a lesser extent, in many other tissues including heart, muscle, kidney and GI tract (Pushkin A et al, 1999).<br><br>SLC4A9 (AE4) was originally thought to exchange Cl- with HCO3- (hence the name AE4) but this has not been reported. Consensus has emerged that it is indeed a Na+/HCO3- co-transporter (Lipovich L et al, 2001). It is predominantly expressed in the kidney, salivary glands, testes, thyroid glands and trachea (Parker MD et al, 2001). has a Stoichiometric coefficient of 3