Interactions of stomach localized bicarbonate transporters AE2 and SLC16A7 with the transmembrane carbonic anhydrase, CAIX

MORGAN PE AND CASEY JR

Niagara –on-the-Lake, Ontario, Canada.

Congreso; 49th Annual meeting and Conference of the Canadian Society of Biochemistry, Molecular Biolgy and Cellular Biology; 2006

Society of Biochemistry, Molecular Biolgy and Cellular Biology

Interaction of stomach localized bicarbonate transporters AE2 and SLC26A7 with the transmembrane carbonic anhydrase, CA IX.Patricio E. Morgan and Joseph R. Casey.Department of Physiology and Department of Biochemistry, University of Alberta, Edmonton, Canada T6G 2H7.  The association of some plasma membrane bicarbonate transporters with carbonic anhydrase enzymes forms a bicarbonate transport metabolon to facilitate metabolic CO2-HCO3- conversion and coupled HCO3- transport.  CAIX is a carbonic anhydrase enzyme with its catalytic site anchored to the extracellular surface through a transmembrane segment.  CAIX has a restricted expression pattern, being highly expressed in gastric mucosa. Its physiological role in stomach its not known but its high expression in parietal cells (PC), suggests a role in acid secretion.  We examined the functional and physical interactions between CAIX and the parietal cell Cl-/HCO3- exchangers including AE2 and SLC26A7.  Co-expression in HEK293 cells of CAIX increased transport activity of AE2 by 28±7%.  In contrast, CAIX did not alter transport by SLC26A7, a recently identified transporter, whose transport rate of 1.5±0.3 mM.min-1 was comparable to AE3.  The increase in transport activity induced by CAIX did not result from altered levels of AE2 expression or cell surface processing.  Immunoprecipitation experiments revealed that CAIX binds AE2 but not SLC26A7.  Purification of carbonic anhydrase from rat stomach preparations with p-amino-benzenesulfonamide coupled to Sepharose resin co-precipitated AE2, suggesting that CAIX-AE2 interaction takes place in vivo.  We conclude that CAIX binds AE2, but not SLC26A7, to form a bicarbonate transport metabolon that is physiologically relevant to gastric HCl secretion.