Carbonic Anhydrase XIV Bound to and Increases the AE3‐mediated Cl−/HCO3− Exchange Activity in the Hypertrophic Heart

Abstract

AE3fl and AE3c anion exchangers catalyze Cl−/HCO3−exchange across cardiomyocyte sarcolemma, to regulate cardiac contractility. AE1 and AE3 proteins associate with carbonic anhydrases (CAII and CAIV), forming a HCO3− transport metabolon (BTM), regulating cardiomyocytes intracellular pH (pHi). Transmembrane CAXIV is also expressed in the myocardium. AE3/CAXIV physical association was examined by coimmunoprecipitation (CoIP) using mouse heart lysates. Both AE3fl and AE3c were IP using anti‐CAXIV Ab, indicating AE3fl‐AE3c/CAXIV interaction in the myocardium. CoIP experiments on heart lysates from an ae3−/− null mouse, failed to pull‐down AE3 with the CAXIV Ab. AE1 protein was also IP by CAXIV Ab from heart lysates. Functional association of AE3fl and CAXIV was examined in hypertrophic rat cardiomyocytes (HRC), monitoring pHi by epifluorescence. HRC presented elevated AE‐mediated Cl−/HCO3−exchange activity compared to normal cardiomyocytes (7.5±1.3 versus 2.9±0.1 mM/min, n=4–6); accompanied by twofold increase of CAXIV protein expression in hypertrophic hearts (HH) (n=11). Benzolamide, a CA‐inhibitor, neutralized the stimulatory effect of extracellular CA on AE3 transport activity (3.7±1.5, n=3), in the HH. CAXIV/AE3 interaction constitutes an extracellular component of a BTM. Increased CAXIV expression and consequent AE3/CAXIV complex formation would render AE3 hyperactive in the HH.Supported by Agencia Nacional de Promoción Científica y Tecnológica (PICT2007 01011, SECyT, Argentina)