Localization of endogenous and recombinant Na⁺-driven anion exchanger protein NDAE1 from Drosophila melanogaster

Na⁺-dependent Cl^-/HCO₃^- exchange activity helps maintain intracellular pH (pH_i) homeostasis in many invertebrate and vertebrate cell types. Our laboratory cloned and characterized a Na⁺-dependent Cl^-/HCO₃^- exchanger (NDAE1) from Drosophila melanogaster (Romero MF, Henry D, Nelson S, Harte PJ, and Sciortino CM. J Biol Chem 275: 24552-24559, 2000). In the present study we used immunohistochemical and Western blot techniques to characterize the developmental expression, subcellular localization, and tissue distribution of NDAE1 protein in D. melanogaster. We have shown that a polyclonal antibody raised against the NH₂ terminus of NDAE1 (αCWR57) recognizes NDAE1 electrophysiologically characterized in Xenopus oocytes. Moreover, our results begin to delineate the NDAE1 topology, i.e., both the NH₂ and COOH termini are intracellular. NDAE1 is expressed throughout Drosophila development in the central and peripheral nervous systems, sensilla, and the alimentary tract (Malpighian tubules, gut, and salivary glands). Coimmunolabeling of larval tissues with NDAE1 antibody and a monoclonal antibody to the Na⁺-K⁺-ATPase α-subunit revealed that the majority of NDAE1 is located at the basolateral membranes of Malpighian tubule cells. These results suggest that NDAE1 may be a key pH_i regulatory protein and may contribute to basolateral ion transport in epithelia and nervous system of Drosophila.