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Am J Physiol Cell Physiol 297: 1091-1102, 2009. First published August 19, 2009; doi:10.1152/ajpcell.00177.2009
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Membrane Transporters, Ion Channels, and Pumps

Bicarbonate homeostasis in excitable tissues: role of AE3 Cl–/HCOFormula exchanger and carbonic anhydrase XIV interaction

Joseph R. Casey,1 William S. Sly,2 Gul N. Shah,2 and Bernardo V. Alvarez3

1Department of Physiology and Department of Biochemistry, Membrane Protein Research Group, University of Alberta, Edmonton, Canada; 2Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri; and 3Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina

Submitted 24 April 2009 ; accepted in final form 16 August 2009

Bicarbonate transport and metabolism are key elements of normal cellular function. Two alternate transcripts of anion exchanger 3 (AE3), full-length (AE3fl) and cardiac (AE3c), are expressed in central nervous system (CNS), where AE3 catalyzes electroneutral Cl–/HCOFormula exchange across the plasma membrane of neuronal and glial cells of CNS. Anion exchanger isoforms, AE3fl and AE3c, associate with the carbonic anhydrases (CA) CAII and CAIV, forming a HCOFormula transport metabolon, to maximize HCOFormula flux across the plasma membrane. CAXIV, with catalytic domain anchored to the extracellular surface, is also expressed in CNS. Here physical association of AE3 and CAXIV was examined by coimmunoprecipitation experiments, using mouse brain and retinal lysates. CAXIV immunoprecipitated with anti-AE3 antibody, and both AE3 isoforms were immunoprecipitated using anti-CAXIV antibody, indicating CAXIV and AE3 interaction in the CNS. Confocal images revealed colocalization of CAXIV and AE3 in Müller and horizontal cells, in the mouse retina. Cl–/HCOFormula exchange activity of AE3fl was investigated in transiently transfected human embryonic kidney 293 cells, using intracellular fluorescence measurements of BCECF, to monitor intracellular pH. CAXIV increased the rate of AE3fl-mediated HCOFormula transport by up to 120%, which was suppressed by the CA inhibitor acetazolamide. Association of AE3 and CAXIV may represent a mechanism to enhance disposal of waste CO2 and to balance pH in excitable tissues.

bicarbonate transport metabolon; AE3/CAXIV complex; central nervous system


Address for reprint requests and other correspondence: B. V. Alvarez, Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, 1900 La Plata, Argentina (e-mail: balvarez{at}med.unlp.edu.ar).






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