Carbonic anhydrase in the adult mosquito midgut

Abstract

SUMMARY We have previously demonstrated the involvement of carbonic anhydrase (CA)in larval mosquito midgut physiology. In this study, we used Hansson's histochemistry to examine the distribution of the enzyme in the midgut of Aedes aegypti, Aedes albopictus, Culex quinquefasciatus, Culex nigripalpus, Ochlerotatus taeniorhynchus, Anopheles albimanus and Anopheles quadrimaculatus adult mosquitoes. Additionally, we quantitated CA content in the anterior and posterior midgut of adult males and females from these species using the 18O isotope exchange method coupled to mass spectrometry. We also tested the effect of CA inhibitors such as methazolamide and acetazolamide in the alkalization of the midgut in females from these species. Our results indicate that CA is present in the midgut of adults from the species studied and that it appears to be preferentially associated with the posterior midgut in both males and females. CA inhibitors appear to have a profound effect on midgut pH indicating that this enzyme might play a key role in the maintenance of this pH.

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

“…The difference may reflect a low level of blood cell lysis in response to early phase trypsin, plus the effects of inward transport of K + . The shift from K + secretion to absorption at 3 h after the blood meal coincides with the introduction into the posterior midgut of late phase trypsin, which is known to digest the majority of the blood meal, releasing 2/3rds of available amino acids (Noriega & Wells, 1999;del Pilar Corena et al, 2005). Cell lysis during the period of late phase trypsin secretion will result in release of intracellular K + from the blood cells.…”

“…It has been suggested that carbonic anhydrase plays a role in this pH increase and when the posterior midgut was treated with the carbonic anhydrase inhibitors methazolamide and acetazolamide it was found that luminal pH decreased (del Pilar Corena et al, 2005). After three hours, however, pH levels within the lumen begin to decrease for the remainder of the blood meal digestion, coincident with the upregulation of the V-ATPase found on the apical membrane of the posterior midgut (Billker et al, 2000;Sanders et al, 2003;Patrick et al, 2006).…”

“…The two main proteases that are known to have a role in the blood meal digestion of A. aegypti are early trypsin and late trypsin which releases approximately 2/3rds of available amino acids from erythrocytes (Noriega & Wells, 1999;del Pilar Corena et al, 2005). Early trypsin mRNA is not found in larvae or pupae, but begins to reach detectable levels in the female 24 hours after eclosion while reaching maximal levels in two to three MSc Thesis -EK Pacey; McMaster University -Department of Biology 6 day-old adults (Noriega & Wells, 1999).…”

“…It has been suggested that carbonic anhydrase activity contributes to the increase in pH in the gut during this digestion (del Pilar Corena et al, 2005).…”

“…During a post prandial diuresis, much of the Na + , Cl -and water in the blood plasma is absorbed across the posterior midgut into the hemolymph, then eliminated through secretion of Na (Patrick et al, 2006). Carbonic anhydrase is associated with the posterior midgut and carbonic anhydrase inhibitors reduce midgut pH in blood-fed mosquitoes, suggesting that the enzyme is implicated in maintenance of the lumen pH (del Pilar Corena et al, 2005). In addition, an isoform of sodium/proton exchanger 3 (NHE3) is found on the basolateral membrane of the anterior and posterior midgut of adult female A. aegypti (Pullikuth et al, 2006 (Farmer et al, 1981).…”