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Articles in PresS, published online ahead of print July 24, 2002
Am J Physiol Cell Physiol, 10.1152/ajpcell.00115.2002
Submitted on March 12, 2002
Accepted on July 17, 2002
1 Physiology, University of Alberta, Edmonton, Alberta, Canada
2 Dipartimento di Chimica, University of Florence, Sesto Fiorentino, Italy
* To whom correspondence should be addressed. E-mail: joe.casey{at}ualberta.ca.
C-terminal cytoplasmic tails of chloride/bicarbonate anion exchangers (AE) bind cytosolic carbonic anhydrase II (CAII) to form a bicarbonate transport metabolon, a membrane protein complex that accelerates transmembrane bicarbonate flux. To determine if interaction with CAII affects the downregulated in adenoma (DRA) chloride/bicarbonate exchanger, anion exchange activity of DRA-transfected HEK 293 cells was monitored by following changes in intracellular pH associated with bicarbonate transport. DRA-mediated bicarbonate transport activity of 18 ± 1 mM H+ equivalents/min was inhibited 53 ± 2 % by 100 µM of the CAII inhibitor, acetazolamide, but was unaffected by the membrane-impermeant carbonic anhydrase inhibitor, 1-[5-Sulfamoyl-1,3,4-thiadiazol-2-yl-(aminosulfonyl-4-phenyl)]-2,,6-dimethyl-4-phenyl-pyridinium perchlorate. Compared with AE1, the C-terminal tail of DRA interacted weakly with CAII. Over-expression of a functionally inactive CAII mutant, V143Y, reduced AE1 transport activity by 61 ± 4%, without effect on DRA transport activity (105 ± 7 % transport activity relative to DRA alone). We conclude that cytosolic CAII is required for full DRA-mediated bicarbonate transport. However, DRA differs from other bicarbonate transport proteins because its transport activity is not stimulated by direct interaction with CAII.
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