Active HCO3- Secretion in the Rectal Salt Gland of A Mosquito Larva Inhabiting NaHCO3–CO3 Lakes

Aedes dorsalis larvae are one of the few organisms capable of inhabiting hypersaline NaHCO3-CO3 lakes. Under laboratory conditions larvae can survive and develop normally in saline media with pH values of 10.5, HCO32 concentrations of 250 mM, or CO32- concentrations of 100 mM. Despite ingestion of alkaline media at a rate equal to 130% of larval body wt/day, these insects regulated haemolymph pH (7.55–770) and HCO3- concentration (8.0–18.5 mM) within narrow limits. Analysis of fluid obtained by micropuncrure or microcannulation indicated that rectal secretion is an important mechanism of pH and HCO3- regulation. The lumen-to-haemocoel HCO3- and CO32- gradients generated by isolated, microcannulated recta were 21:1 and 241:1, respectively. Transepithelial potential in cannulated recta was −4.2 to −25.3 mV (lumen negative), demonstrating that net HCO3- secretion occurs against a large electrochemical gradient. Note: