title: PAT-1 (Slc26a6) is the predominant apical membrane Cl-/HCO3- exchanger in the upper villous epithelium of the murine duodenum.
abstract: Basal HCO(3)(-) secretion across the duodenum has been shown in several species to principally involve the activity of apical membrane Cl(-)/HCO(3)(-) exchanger(s). To investigate the identity of relevant anion exchanger(s), experiments were performed using wild-type (WT) mice and mice with gene-targeted deletion of the following Cl(-)/HCO(3)(-) exchangers localized to the apical membrane of murine duodenal villi: Slc26a3 [down-regulated in adenoma (DRA)], Slc26a6 [putative anion transporter 1 (PAT-1)], and Slc4a9 [anion exchanger 4 (AE4)]. RT-PCR of the isolated villous epithelium demonstrated PAT-1, DRA, and AE4 mRNA expression. Using the pH-sensitive dye BCECF, anion exchange rates were measured across the apical membrane of epithelial cells in the upper villus of the intact duodenal mucosa. Under basal conditions, Cl(-)/HCO(3)(-) exchange activity was reduced by 65-80% in the PAT-1(-) duodenum, 30-40% in the DRA(-) duodenum, and <5% in the AE4(-) duodenum compared with the WT duodenum. SO(4)(2-)/HCO(3)(-) exchange was eliminated in the PAT-1(-) duodenum but was not affected in the DRA(-) and AE4(-) duodenum relative to the WT duodenum. Intracellular pH (pH(i)) was reduced in the PAT-1(-) villous epithelium but increased to WT levels in the absence of CO(2)/HCO(3)(-) or during methazolamide treatment. Further experiments under physiological conditions indicated active pH(i) compensation in the PAT-1(-) villous epithelium by combined activities of Na(+)/H(+) exchanger 1 and Cl(-)-dependent transport processes at the basolateral membrane. We conclude that 1) PAT-1 is the major contributor to basal Cl(-)/HCO(3)(-) and SO(4)(2-)/HCO(3)(-) exchange across the apical membrane and 2) PAT-1 plays a role in pH(i) regulation in the upper villous epithelium of the murine duodenum.
authors.affiliation: Department of Biomedical Sciences, University of Missouri, Columbia, MO, USA.
authors.forename: Janet E
authors.initials: JE
authors.lastname: Simpson
authors.forename: Clifford W
authors.initials: CW
authors.lastname: Schweinfest
authors.forename: Gary E
authors.initials: GE
authors.lastname: Shull
authors.forename: Lara R
authors.initials: LR
authors.lastname: Gawenis
authors.forename: Nancy M
authors.initials: NM
authors.lastname: Walker
authors.forename: Kathryn T
authors.initials: KT
authors.lastname: Boyle
authors.forename: Manoocher
authors.initials: M
authors.lastname: Soleimani
authors.forename: Lane L
authors.initials: LL
authors.lastname: Clarke
mesh_terms: D000818:Animals; D017920:Antiporters / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism; D015194:Diffusion Chambers, Culture; D004386:Duodenum / Q000166:cytology / Q000378:metabolism*; D015870:Gene Expression; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000074082:Sodium-Hydrogen Exchanger 1; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D000076988:Sulfate Transporters; D013431:Sulfates / Q000378:metabolism; D013997:Time Factors; D046509:Tissue Culture Techniques
chemical_list: D017920:Antiporters; D001639:Bicarbonates; D027682:Cation Transport Proteins; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D008565:Membrane Proteins; D012333:RNA, Messenger; C489860:Slc26a3 protein, mouse; C466900:Slc26a6 protein, mouse; C480025:Slc4a9 protein, mouse; C490997:Slc9a1 protein, mouse; D000074082:Sodium-Hydrogen Exchanger 1; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D000076988:Sulfate Transporters; D013431:Sulfates; D019005:Cystic Fibrosis Transmembrane Conductance Regulator