SUMMARY The gut contents of larval mosquitoes are alkalinized by the anterior midgut and reacidified by the posterior midgut. In the present study the cellular mechanisms of reacidification were studied in isolated, perfused posterior midgut by measuring the transepithelial voltage (Vte) and the rate of acid secretion as indicated by the color change of m-cresol purple during intervals of perfusion stop. The lumen-positive Vte and reacidification were significantly increased by serotonin (0.2 μmol l−1). The V-type H+-ATPase inhibitor concanamycin A (10 μmol l−1) on the luminal side inhibited acidification and decreased Vte. On the hemolymph side the carbonic anhydrase (CA) inhibitor acetazolamide (1 mmol l−1) almost abolished Vte, but had no effect on acidification. Similarly, hemolymph-side DIDS (0.1 mmol l−1), DPC (0.5 mmol l−1), amiloride (1 mmol l−1) and ouabain (2.5 mmol l−1) significantly reduced Vte, whereas Ba2+ (5 mmol l−1) was without effect. DPC and amiloride also reduced Vte when applied to the luminal side of the epithelium. Unilateral substitution of gluconate for Cl− affected Vte in a way consistent with a greater permeability for Cl−versus Na+. Cl− replacement in the lumen decreased Vte, whereas replacement on the hemolymph side increased it. Bilateral replacement left the control voltage unaffected. Na+ replacement on either side of the tissue reduced Vte to different degrees. Omission of luminal amino acids was followed by a significant decrease in Vte. Except for concanamycin A, none of the above manipulations impaired acidification, indicating that acidification requires only the apical proton pump. However, the chemical source of secreted H+ is still unknown and needs to be investigated.

A resistant strain (DR) of Aedes aegypti, generated by deltamethrin selection for 20 consecutive generations from a laboratory susceptible strain (DS) was studied for the possible resistant mechanisms. The pyrethroid resistance developed was characterized by biochemical assays and native polyacrylamide gel electrophoresis. Significant elevation in the activity of alpha- and beta-esterases, glucose-6-phosphate dehydrogenase (G6PD), CYTP450 (CYTP450), and glutathione-s-transferase (GST) were noticed in DR. The gel profiles for esterases, G6PD, and CYTP450 were different in DR as compared to DS strain. The difference was either in the form of additional bands or increased intensity of the bands or both. Gel profile variations were also evident from densitometry. Our study suggests that these enzymes play an important role in deltamethrin resistance in the DR strain.

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