Ae. aegypti is a freshwater culicine that can acclimate to 50% ASW by osmoconforming in water hyper osmotic to their hemolymph . Larvae possess a nonsegmented rectum which selectively resorbs ions from the primary urine. Like Ae. aegypti, anophelines reared in freshwater actively resorb ions from the environment and their urine to maintain constant ionic and osmotic hemolymph concentrations . The combination of basal Na K ATPase and apical VATPase in the rectum is ideally suited for this task. The polarity is similar to that in frog skin , where the V ATPase hyperpolarizes the apical membrane, which drives Na into the cell from the Na deficient environment. The Na K ATPase then transports the Na across the basal membrane into the hemolymph, replenishing ions which are lost to the aquatic environment, as first suggested by . One example of V ATPase mediated Na transport into mosquito cells occurs in the alimentary canal of many species: Na is driven into the cell by the electrical coupling of a V ATPase and a Na : amino acid nutrient amino acid transporter .
Hyperpolarization of the apical membrane by V ATPase drives electrophoretic Na : amino acid symport into the cells. The efflux of H and influx of Na driven by the coupling of these two proteins constitutes a Na H exchanger , NHEV NAT . In addition to driving Na , V ATPase supplier PD 98059 hyperpolarization of the apical membrane may drive the absorption of numerous other essential ions. In Oc. taeniorhynchus reared in freshwater, a similar synergy between V ATPase and Na K ATPase is evident in the AR, a region that has a resorptive function . This finding provides further support that the physiological coupling between these ATPases is involved in resorbing essential ions from the primary urine. Importantly, when Oc. taeniorhynchus are reared in 100% ASW, the apical V ATPase appears to localize to the cytoplasm, breaking the coupling with Na K ATPase, which may indicate that these cells decrease their resorptive function in the presence of high salinity.
The cytoplasmic localization of V ATPase, a membrane protein, in the DAR cells of both An. gambiae and An. albimanus, as well as in the AR of saline reared Oc. taeniorhynchus was unexpected, although there are several possible explanations. The rectal ultrastructure of the DAR cells has not been extensively studied, but the AR of saline tolerant culicines exhibits a highly infolded Maraviroc basal membrane which constitutes the major elaboration of the surface area . The apparent cytoplasmic V ATPase may instead be localizing to these basal infoldings. Alternatively, this localization could represent V ATPase protein on the membrane of vacuoles within the cells or subunits that have dissociated from their membrane bound V0 anchors.