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

Abstract

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, HCO3− 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 (7·55–7·70) and HCO3− concentration (8·0–18·5 mm) within narrow limits. Analysis of fluid obtained by micropuncture 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 – 14·2 to –23·3 mV (lumen negative), demonstrating that net HCO3− secretion occurs against a large electrochemical gradient.