Signaling by intracellular Ca2+ and H+ in larval mosquito (Aedes aegypti) midgut epithelium in response to serosal serotonin and lumen pH.

The midgut of larval mosquitoes (Aedes aegypti) mediates a cycle of alkali secretion in the anterior segment (AMG) followed by partial reacidification in the posterior segment (PMG); both processes are serotonin-dependent. Here we report that intracellular Ca(2+)(Ca(i)(2+)) as indicated by Fura-2 fluorescence, is elevated in both tissues in response to serotonin, but the time courses differ characteristically in the two gut segments, and Ca(2+)-free solution abolishes the serotonin response in AMG, but not in PMG, whereas Thapsigargin, an inhibitor of endoplasmic Ca(2+) transport, abolished responsiveness to 5-HT in PMG. These results suggest the origins for the Ca(2+) signal differ between the two tissues. Quantitative real-time RT-PCR revealed expression of 5 putative 5-HT receptor types in AMG, including 5-HT(2)-like receptors which would be expected to initiate a Ca(2+) signal. None of these receptors were highly expressed in PMG. Cyclic AMP (cAMP) is a secretagogue for both tissues, but H89, an inhibitor of Protein Kinase A (PKA), is also a secretagogue, suggesting that the stimulatory effect of cAMP involves a non-PKA pathway. Cytochalasins B and D block the effect of 5-HT in AMG, suggesting a vesicle-fusion mechanism of activation of the basal V-ATPase in this tissue. Finally, in PMG, elevation of luminal pH increases (Ca(i)(2+)) and decreases intracellular pH as measured by BCECF fluorescence. These responses suggest that the rate of acid secretion by PMG might be responsive to local demand for luminal reacidification as well as to serosal serotonin.

Biochemical characterization of deltamethrin resistance in a laboratory-selected strain of Aedes aegypti.

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.