Aquaporin homologs and water transport in the anal papillae of the larval mosquito, Aedes aegypti

The hemolymph osmolarity of the freshwater mosquito larvae (Aedes aegypti) is greater than that of their habitat. To combat the influx of water, larvae cycle water entering through the gut and anal papillae to the Malpighian tubules for secretion. The presence of aquaporins (AQPs, water channels) may facilitate the movement of water across these tissues. Tissue distribution of mRNA transcripts of putative aquaporins from mosquito larvae, using quantitative PCR, revealed expression of transcripts in the Malpighian tubules and anal papillae. Four putative aquaporin transcripts are expressed in the Malpighian tubules and provide a basis for further work aimed at discovering the elusive water transporters functioning during diuresis. Transcripts of putative AQPs (AaAQP4 and AaAQP1b) are expressed in the anal papillae. Immunoreactivity to a human AQP1-antibody was found in the anal papillae and mercury inhibits tritiated water uptake in isolated anal papillae. Together, the results suggest that AQP(s) could be responsible for facilitating water transport at the papillae epithelium.