Pharmacological characterisation of apical Na+ and Cl- transport mechanisms of the anal papillae in the larval mosquito Aedes aegypti

The anal papillae of freshwater mosquito larvae are important sites of NaCl uptake, thereby acting to offset the dilution of the hemolymph by the dilute habitat. The ion-transport mechanisms in the anal papillae are not well understood. In this study, the scanning ion-selective electrode technique (SIET) was utilized to measure ion fluxes at the anal papillae, and pharmacological inhibitors of ion transport were utilized to identify ion-transport mechanisms. Na+ uptake by the anal papillae was inhibited by bafilomycin and phenamil but not by HMA. Cl-uptake was inhibited by methazolamide, SITS and DIDS but not by bafilomycin. H+ secretion was inhibited by bafilomycin and methazolamide. Ouabain and bumetanide had no effect on NaCl uptake or H+ secretion. Together, the results suggest that Na+ uptake at the apical membrane occurs through a Na+ channel that is driven by a V-type H+-ATPase and that Cl-uptake occurs through a Cl-/HCO3- exchanger, with carbonic anhydrase providing H+ and HCO3- to the V-type H+-ATPase and exchanger, respectively.