The physiology of the midgut of Lutzomyia longipalpis (Lutz and Neiva 1912): pH in different physiological conditions and mechanisms involved in its control
2008
SUMMARY Nutrient digestion and absorption after blood feeding are important events
for Lutzomyia longipalpis , which uses these nutrients to produce
eggs. In this context, the pH inside the digestive tract is an important
physiological feature as it can markedly influence the digestive process as
well as interfere with Leishmania development in infected
phlebotomines. It was described previously that unfed females have an acidic
midgut (pH 6). In this study, the pH inside the midgut of blood-fed females
was measured. The abdominal midgut (AM) pH varied from 8.15±0.31 in the
first 10 h post-blood meal to 7.7±0.17 after 24 h. While the AM was
alkaline during blood digestion, the pH in the thoracic midgut (TM) remained
acidic (5.5–6.0). In agreement with these findings, the enzymeα
-glucosidase, which has an optimum pH of 5.8, is mainly encountered in
the acidic TM. The capacity of unfed females to maintain the acidic intestinal
pH was also evaluated. Our results showed the presence of an efficient
mechanism that maintains the pH almost constant at about 6 in the midgut, but
not in the crop. This mechanism is promptly interrupted in the AM by blood
ingestion. RT-PCR results indicated the presence of carbonic anhydrase in the
midgut cells, which apparently is required to maintain the pH at 6 in the
midgut of unfed females. Investigations on the phenomenon of alkalization
observed after blood ingestion indicated that two mechanisms are involved: in
addition to the alkalization promoted by CO 2 volatilization there
is a minor contribution from a second mechanism not yet characterized. Some
inferences concerning Leishmania development and pH in the digestive
tube are presented.
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