Transport of H+, Na+ and K+ across the posterior midgut of blood-fed mosquitoes (Aedes aegypti)

Abstract

Mosquitoes pose significant threats to human health because they act as vectors for disease causing viruses and protozoans. Indeed, Aedes aegypti is known as the Yellow Fever Mosquito because of its role as a vector for viral infections that kill thousands of people each year. A more thorough understanding of mosquito physiology will aid development of novel control strategies. Previous work on ion transport across the midgut has been focused primarily on larval A. aegypti, while research on the midgut of the adult stage is less complete. The posterior midgut of the adult female is of particular interest because it is used for the storage and digestion of the blood meal which is required for the production of eggs. This study used an array of electrophysiological methodologies such as the Scanning Ion Electrode Technique (SIET) in order to elucidate the patterns and mechanisms of Na + , H + and K + transport across the posterior midgut at intervals during postprandial diuresis and digestion of the blood meal. Measurements of transepithelial potential indicated that the lumen was at its most negative (-13.2 mV) three hours after the blood meal and then gradually became less negative during the time course of digestion. Na + was absorbed (from lumen to bath) at all intervals after the blood meal (6 min, 30 min, 2h, 24 h); calculations of the electrochemical potential indicated that absorption required active transport. H + absorption at all times (6 min -48 h) after the blood meal was also active (i.e. against the electrochemical gradient for H + ) and was greatly reduced by inhibition of carbonic anhydrase. K + transport across the midgut exhibited two distinct phases. During diuresis, luminal concentrations of K + were in the range 24 -28 mM and secretion into the midgut was opposed by the electrochemical iv gradient, indicating active transport. After diuresis, during blood meal digestion, concentrations of K + in the midgut contents were high (95 -134 mM) and absorption of K + was favoured by the electrochemical gradient. K + absorption was sensitive to the channel blocker Ba 2+ during this period.v Acknowledgements

An insecticide resistance-breaking mosquitocide targeting inward rectifier potassium channels in vectors of Zika virus and malaria

“…The inhibition of Kir channels in Malpighian tubules is expected to disrupt the processing of blood meals by limiting the excretion of blood-derived electrolytes and water that are absorbed into the hemolymph. In addition, potential effects on the midgut’s digestion of blood and absorption of ions/fluid from the blood cannot be ruled out given that the mosquito midgut is a site of Kir mRNA expression and barium-sensitive K + transport283738. Our experiments in An.…”

Characterization of Carbonic Anhydrase 9 in the Alimentary Canal of Aedes aegypti and Its Relationship to Homologous Mosquito Carbonic Anhydrases

“…We used molecular phylogenetics, data mining of transcriptomes, molecular biology, and immunohistochemistry to characterize AeCA9 as a soluble cytoplasmic protein in the adult and larval alimentary canal. This work gives greater resolution to the mechanisms of pH regulation and proton transport from past studies [3,32]. Del Pilar Corena et al [3] suggested that CAs play a role in pH regulation of the gut, and these current studies show that AeCA9 is one of the CAs found in the gut tissues.…”

“…We hypothesize that the products of AeCA9 activity play roles in pH regulation, fluid secretion, and amino acid transport [23,48]. This hypothesis is adapted from the model proposed by Pacey and O′Donnell [32]. AeCA9 may provide H + for the transepithlial potential established by H + V-ATPase, which drives the displacement of ions across biological membranes for pH and ion regulatory processes.…”

“…The remaining CA isoforms in both species are uncharacterized. CAs have been analyzed in terms of their capacity to influence the pH in the adult gut lumen [3] and effect proton transport following a blood meal [32]. In both of those studies, the isoforms of CA in the midgut that could be involved with ion transport and pH regulation were not determined.…”

Blood serum and BSA, but neither red blood cells nor hemoglobin can support vitellogenesis and egg production in the dengue vector Aedes aegypti

“…aegypti is an invasive species in the Americas, preferring areas close to humans where blood is easily accessible (Powell and Tabachnick 2013). After a female takes a blood meal into their midgut, the blood proteins are enzymatically digested into amino acids, which are then released into the hemolymph (Pacey and O'Donnell 2014). The accumulated amino acids in the hemolymph are absorbed by the mosquito fat body, functionally similar to the vertebrate liver, which synthesizes yolk protein precursors (YPP), called vitellogenin.…”