The physiology of the midgut ofLutzomyia longipalpis(Lutz and Neiva 1912): pH in different physiological conditions and mechanisms involved in its control

Abstract

SUMMARYNutrient 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 enzyme α-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.

Mechanisms of pH control in the midgut ofLutzomyia longipalpis: roles for ingested molecules and hormones

“…We have previously reported that the pH of the diverticulum in L. longipalpis females assumes the value of the ingested food, reflecting an unbuffered condition (Santos et al, 2008). However, the pH in the abdominal midgut is rigorously adjusted according to the physiological state.…”

“…However, the pH in the abdominal midgut is rigorously adjusted according to the physiological state. In unfed or sugar-fed insects, the midgut pH is actively maintained at ~6, even when it is challenged by ingestion of strong buffered solutions such as 0.16moll -l HEPES pH7.5 or 0.16moll -l MES pH5.0 (Santos et al, 2008). The intestinal enzyme -glucosidase, which digests carbohydrates that are typically found in the sugar diet, requires an acidic pH (Gontijo et al, 1998;Jacobson et al, 2001).…”

“…The intestinal enzyme -glucosidase, which digests carbohydrates that are typically found in the sugar diet, requires an acidic pH (Gontijo et al, 1998;Jacobson et al, 2001). When blood is ingested, it is stored in the abdominal midgut, where the mechanism responsible for maintaining the pH at 6 is immediately switched off, allowing alkalization to pH8.15 (Santos et al, 2008). This switch must occur because an alkaline pH is required for blood digestion by the exoproteases trypsin and quimotrypsin, which are enzymes with alkaline optimum pH values (Terra and Ferreira, 1994).…”

“…Even when the abdominal midgut is alkaline as a consequence of blood ingestion, carbohydrate digestion in the thoracic midgut continues normally because this region remains acidic (pH6). This enables action of -glucosidase, which is concentrated in this region and is bound to the microvilli of the enterocytes (Gontijo et al, 1998;Santos et al, 2008).…”

“…The first occurs as a consequence of the loss of CO 2 from blood (CO 2 volatilization) according to the equation CO 2 +H 2 O}H 2 CO 3 }HCO 3 -+H + (Santos et al, 2008). The second mechanism has not yet been characterized (Santos et al, 2008).…”