Functional activity of Pat-1 (Slc26a6) Cl(−)/HCO₃(−) exchange in the lower villus epithelium of murine duodenum.
OBJECTIVE
The apical membrane anion exchanger putative anion transporter-1 (Pat-1) is expressed at significant levels in the lower villus epithelium of murine duodenum. However, previous studies of Cl(−)/HCO₃(−) exchange in the lower villus have failed to demonstrate Pat-1 function. Those studies routinely included luminal glucose which induces Na(+) -coupled glucose transport and acidifies the villus epithelium. Since Pat-1 has been proposed to be an electrogenic 1Cl(−)/2HCO₃(−) exchanger, membrane depolarization or cell acidification during glucose transport may obscure Pat-1 activity. Therefore, we investigated the effects of luminal glucose on Cl(−)(IN)/HCO₃(−) (OUT) exchange activity in the lower villus epithelium.


METHODS
Cl(−)(IN) /HCO (−) (OUT) exchange of villus epithelium in duodenal mucosa from Pat-1 knockout (KO), Slc26a3 [down-regulated in adenoma (Dra)] KO, cystic fibrosis transmembrane conductance regulator (Cftr) KO and wild-type (WT) littermate mice was measured using the pH-sensitive dye 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein. Short-circuit current (I(sc) ) was measured in Ussing chambers.


RESULTS
During glucose absorption, Cl(−)(IN)/HCO₃(−) (OUT) exchange in the lower villus epithelium was abolished in the Dra KO and unaffected in the Pat-1 KO relative to WT. However, during electroneutral mannose absorption or electrogenic α-D-methyl glucoside absorption, Cl(−)(IN) /HCO₃(−) (OUT) exchange was reduced in both Pat-1 KO and Dra KO villi. Exposure to high [K(+)] abolished Cl(−)(IN) /HCO₃(−) (OUT) exchange in the Dra KO but not the Dra/Cftr double KO epithelium, suggesting that Pat-1 activity is little affected by membrane depolarization except in the presence of Cftr.


CONCLUSIONS
The metabolic and electrogenic activity of glucose transport obscures Cl(−)(IN) /HCO₃(−) (OUT) exchange activity of Pat-1 in the lower villus. The inhibitory effects of membrane depolarization on Pat-1 Cl(−)(IN) /HCO₃(−) (OUT) exchange may require concurrent membrane association with Cftr.
Walker
N M
NM
Dalton Cardiovascular Research Center, University of Missouri, Columbia, 65211, USA.
Simpson
J E
JE
Hoover
E E
EE
Brazill
J M
JM
Schweinfest
C W
CW
Soleimani
M
M
Clarke
L L
LL
D000818:Animals; D017920:Antiporters / Q000235:genetics / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters / Q000235:genetics / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D004386:Duodenum / Q000033:anatomy & histology* / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000033:anatomy & histology* / Q000378:metabolism*; D008358:Mannose / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D011188:Potassium / Q000378:metabolism; D000076988:Sulfate Transporters
D017920:Antiporters; D001639:Bicarbonates; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; C466900:Slc26a6 protein, mouse; D000076988:Sulfate Transporters; D005947:Glucose; D008358:Mannose; D011188:Potassium