D.F.MOFFETT*; S.B.MOFFETT; M.F.ROMERO: Immunolocalization of Na+-dependent anion exchanger (NDAE1) in anterior stomach of mosquito larvae (Aedes aegypti): relevance to gut alkalinization.

A Na⁺-dependent anion exchanger (NDAE1) with homology to vertebrate bicarbonate transporters has recently been cloned from Drosophila and expressed in Xenopus oocytes.* In its orthograde mode NDAE1 mediates extrusion of Cl^– and/or H⁺ in exchange for entry of Na⁺ and HCO₃^–. NDAE1, like other bicarbonate transporters, is likely involved in both cytoplasmic acid-base homeostasis and transepithelial acid and alkali secretion. In these studies, fluorescence immunohistochemistry against several conserved epitopes of NDAE1 showed localization in anterior stomach (and other epithelia and CNS neurons) of mosquito larvae. The anterior stomach generates a luminal pH of ~10; the cellular mechanisms of this active alkali secretion are largely unknown. In the anterior stomach, NDAE1 immunoreactivity was abundant in basolateral plasma membranes. This location is consistent with a model of alkalinization driven by tandem operation of basolateral Na⁺/K⁺ ATPase and electrogenic V-type H⁺ ATPase. The large electrochemical gradient for Na⁺ created by these pumps would provide the necessary ionic gradients for NDAE1, driving H⁺ from cell to hemolymph and HCO₃^– from hemolymph to cytoplasm. Since NDAE1 also appears in apical cell membranes, and since mosquito larvae ingest their very-low-Na⁺ freshwater medium, it may function in the antigrade mode in apical membranes, mediating cell-to-lumen movement of Na⁺ and HCO₃^–. *Romero et al. (2000) J. Biol Chem. 275, 24552.