The anterior midgut of larval yellow fever mosquitoes (Aedes aegypti): effects of amino acids, dicarboxylic acids, and glucose on the transepithelial voltage and strong luminal alkalinization

Abstract

Isolated anterior midguts of larval Aedes aegypti were bathed in aerated mosquito saline containing serotonin (0.2 micromol L(-1)) and perfused with NaCl (100 mmol L(-1)). The lumen negative transepithelial voltage (V(te)) was measured and luminal alkalinization was determined through the color change of luminal m-cresol purple from yellow to purple after luminal perfusion stops. Addition of 10 mmol L(-1) amino acids (arginine, glutamine, histidine or proline) or dicarboxylic acids (malate or succinate) to the luminal perfusate resulted in more negative V(te) values, whereas addition of glucose was without effect. In the presence of TRIS chloride as luminal perfusate, addition of nutrients did not change V(te). These results are consistent with Na(+)-dependent absorption of amino acids and dicarboxylic acids. Effects of serotonin withdrawal indicated that nutrient absorption is stimulated by this hormone. Strong luminal alkalinization was observed with mosquito saline containing serotonin on the hemolymph-side and 100 mmol L(-1) NaCl in the lumen, indicating that alkalinization does not depend on luminal nutrients. Omission of glucose or dicarboxylic acids from the hemolymph-side solution had no effect on luminal alkalinization, whereas omission of amino acids significantly decelerated it. Re-addition of amino acids restored alkalinization, suggesting the involvement of amino acid metabolism in luminal alkalinization.