Molecular physiology of SLC4 anion exchangers

Exp Physiol. 2006 Jan;91(1):153-61. doi: 10.1113/expphysiol.2005.031765. Epub 2005 Oct 20.


Plasmalemmal Cl- -HCO3- exchangers regulate intracellular pH and [Cl-] and cell volume. In polarized epithelial cells, they contribute also to transepithelial secretion and reabsorption of acid-base equivalents and of Cl-. Members of both the SLC4 and SLC26 mammalian gene families encode Na+-independent Cl- -HCO3- exchangers. Human SLC4A1/AE1 mutations cause either the erythroid disorders spherocytic haemolytic anaemia or ovalocytosis, or distal renal tubular acidosis. SLC4A2/AE2 knockout mice die at weaning. Human SLC4A3/AE3 polymorphisms have been associated with seizure disorder. Although mammalian SLC4/AE polypeptides mediate only electroneutral Cl- -anion exchange, trout erythroid AE1 also promotes osmolyte transport and increased anion conductance. Mouse AE1 is required for DIDS-sensitive erythroid Cl- conductance, but definitive evidence for mediation of Cl- conductance is lacking. However, a single missense mutation allows AE1 to mediate both electrogenic SO4(2-) -Cl- exchange or electroneutral, H+-independent SO4(2)- -SO4(2-) exchange. In the Xenopus oocyte, the AE1 C-terminal cytoplasmic tail residues reported to bind carbonic anhydrase II are dispensable for Cl- -Cl- exchange, but required for Cl- -HCO3- exchange. AE2 is acutely and independently inhibited by intracellular and extracellular H+, and this regulation requires integrity of the most highly conserved sequence of the AE2 N-terminal cytoplasmic domain. Individual missense mutations within this and adjacent regions identify additional residues which acid-shift pHo sensitivity. These regions together are modelled to form contiguous surface patches on the AE2 cytoplasmic domain. In contrast, the N-terminal variant AE2c polypeptide exhibits an alkaline-shifted pHo sensitivity, as do certain transmembrane domain His mutants. AE2-mediated anion exchange is also stimulated by ammonium and by hypertonicity by a mechanism sensitive to inhibition by chelation of intracellular Ca2+ and by calmidazolium. This growing body of structure-function data, together with increased structural information, will advance mechanistic understanding of SLC4 anion exchangers.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Review

MeSH terms

  • Acidosis, Renal Tubular / genetics
  • Acidosis, Renal Tubular / metabolism
  • Amino Acid Sequence
  • Animals
  • Anion Exchange Protein 1, Erythrocyte / chemistry
  • Anion Exchange Protein 1, Erythrocyte / genetics
  • Anion Exchange Protein 1, Erythrocyte / metabolism*
  • Anion Transport Proteins / chemistry
  • Anion Transport Proteins / genetics
  • Anion Transport Proteins / metabolism*
  • Antiporters / chemistry
  • Antiporters / genetics
  • Antiporters / metabolism*
  • Carbonic Anhydrases / metabolism
  • Chloride-Bicarbonate Antiporters / chemistry
  • Chloride-Bicarbonate Antiporters / genetics
  • Chloride-Bicarbonate Antiporters / metabolism
  • Elliptocytosis, Hereditary / genetics
  • Elliptocytosis, Hereditary / metabolism
  • Humans
  • Hydrogen-Ion Concentration
  • Molecular Sequence Data
  • Multigene Family
  • Mutation
  • Polymorphism, Genetic
  • Protein Conformation
  • SLC4A Proteins
  • Spherocytosis, Hereditary / genetics
  • Spherocytosis, Hereditary / metabolism
  • Structure-Activity Relationship


  • Anion Exchange Protein 1, Erythrocyte
  • Anion Transport Proteins
  • Antiporters
  • Chloride-Bicarbonate Antiporters
  • SLC4A Proteins
  • SLC4A1 protein, human
  • SLC4A2 protein, human
  • SLC4A3 protein, human
  • Slc4a2 protein, mouse
  • Carbonic Anhydrases