Native and recombinant Slc26a3 (downregulated in adenoma, Dra) do not exhibit properties of 2Cl-/1HCO3- exchange

Am J Physiol Cell Physiol. 2011 Feb;300(2):C276-86. doi: 10.1152/ajpcell.00366.2010. Epub 2010 Nov 10.

Abstract

The recent proposal that Dra/Slc26a3 mediates electrogenic 2Cl(-)/1HCO(3)(-) exchange suggests a required revision of classical concepts of electroneutral Cl(-) transport across epithelia such as the intestine. We investigated 1) the effect of endogenous Dra Cl(-)/HCO(3)(-) activity on apical membrane potential (V(a)) of the cecal surface epithelium using wild-type (WT) and knockout (KO) mice; and 2) the electrical properties of Cl(-)/(OH(-))HCO(3)(-) exchange by mouse and human orthologs of Dra expressed in Xenopus oocytes. Ex vivo (36)Cl(-) fluxes and microfluorometry revealed that cecal Cl(-)/HCO(3)(-) exchange was abolished in the Dra KO without concordant changes in short-circuit current. In microelectrode studies, baseline V(a) of Dra KO surface epithelium was slightly hyperpolarized relative to WT but depolarized to the same extent as WT during luminal Cl(-) substitution. Subsequent studies indicated that Cl(-)-dependent V(a) depolarization requires the anion channel Cftr. Oocyte studies demonstrated that Dra-mediated exchange of intracellular Cl(-) for extracellular HCO(3)(-) is accompanied by slow hyperpolarization and a modest outward current, but that the steady-state current-voltage relationship is unaffected by Cl(-) removal or pharmacological blockade. Further, Dra-dependent (36)Cl(-) efflux was voltage-insensitive in oocytes coexpressing the cation channels ENaC or ROMK. We conclude that 1) endogenous Dra and recombinant human/mouse Dra orthologs do not exhibit electrogenic 2Cl(-)/1HCO(3)(-) exchange; and 2) acute induction of Dra Cl(-)/HCO(3)(-) exchange is associated with secondary membrane potential changes representing homeostatic responses. Thus, participation of Dra in coupled NaCl absorption and in uncoupled HCO(3)(-) secretion remains compatible with electroneutrality of these processes, and with the utility of electroneutral transport models for predicting epithelial responses in health and disease.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Antiporters / genetics
  • Antiporters / metabolism*
  • Bicarbonates / metabolism
  • Cecum / metabolism
  • Chloride-Bicarbonate Antiporters / genetics
  • Chloride-Bicarbonate Antiporters / metabolism*
  • Chlorides / metabolism
  • Cystic Fibrosis Transmembrane Conductance Regulator / metabolism
  • Cystic Fibrosis Transmembrane Conductance Regulator / physiology
  • Female
  • Humans
  • Male
  • Membrane Potentials
  • Mice
  • Mice, Knockout
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Sulfate Transporters

Substances

  • Antiporters
  • Bicarbonates
  • Chloride-Bicarbonate Antiporters
  • Chlorides
  • Recombinant Proteins
  • SLC26A3 protein, human
  • Slc26a3 protein, mouse
  • Sulfate Transporters
  • Cystic Fibrosis Transmembrane Conductance Regulator