Bicarbonate Homeostasis in Excitable Tissues: Role of AE3 Cl-/HCO3- Exchanger and Carbonic Anhydrase XIV Interaction.

CASEY, JR; SLY, WS; SHAH, GN; ALVAREZ, BV

AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY

AMER PHYSIOLOGICAL SOC

Lugar: Bethesda, MD; Año: 2009 vol. 297 p. 1091 - 1102

0363-6143

Bicarbonate transport and metabolism are key elements of normal cellular function.  Two alternate transcripts of AE3, full-length (AE3fl) and cardiac (AE3c), are expressed in central nervous system (CNS) where AE3 catalyzes electroneutral Cl-/HCO3- 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 HCO3- transport metabolon, to maximize HCO3- 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 co-immunoprecipitation 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 co-localization of CAXIV and AE3 in Müller and horizontal cells, in the mouse retina.  Cl-/HCO3- exchange activity of AE3fl was investigated in transiently-transfected HEK293 cells, using intracellular fluorescent measurements of 2´-7´-bis (2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF), to monitor intracellular pH.  CAXIV increased the rate of AE3fl-mediated HCO3- 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.