Discussion Ion regulation by the rectum helps mosquito larvae to survive, and adapt to, a constantly changing environment. A wealth of literature has focused on the structure and function of the larval culicine rectum and the distinction between its role in freshwater and saline tolerant species . However, the discovery that the anopheline rectum is structurally distinct from any culicine species described suggested that anophelines may utilize a unique method of ion regulation. To test this hypothesis, we compared the localization patterns of three proteins involved in ion regulation in the recta of anopheline and culicine larvae reared in fresh versus saline water. Three key points regarding the comparison of anopheline and culicine recta emerge from these data: In contrast to obligate freshwater and saline tolerant culicines which have structurally distinct recta, all anophelines examined possess a similarly structured rectum, consisting of DAR and non DAR cells .
Anopheline larvae undergo a dramatic shift in rectal Na K ATPase localization when reared in NVP-BGJ398 freshwater versus saline water. This shift is not seen in any culicine larvae examined. With the exception of Ae. aegypti, CA9 consistently localized to an anterior region of the rectum in both culicine and anopheline larvae regardless of the salinity of the rearing water. The first two key points, along with the localization patterns of Na K ATPase and V ATPase , will be used to suggest putative functions for the anopheline rectal regions. Localization of CA9 will be discussed in a separate section. Figs 4 and 5 summarize our results; Fig. 4 illustrates the differences between anopheline and culicine recta and Fig. 5 summarizes protein localization in anophelines and culicines in a schematic form. When reared in freshwater, the protein localization patterns in An. gambiae and An. albimanus recta were identical: non DAR cells contained an apical V ATPase and basal Na K ATPase whereas the DAR cells were enriched in cytoplasmic V ATPase.
The protein localization pattern of the non DAR cells in An. gambiae and An. albimanus was similar to that price Sodium valproate selleck of the freshwater culicine, Ae. aegypti, which also expressed an apical V ATPase and basal Na K ATPase in its non segmented rectum. The detection of V ATPase in Ae. aegypti larval rectum confirms the finding of Filippova et al. but conflicts with the findings of Patrick et al. who detected V ATPase mRNA in the rectum, but did not detect protein when using the same antibody against the B subunit which was used in this study. However, ultrastructural studies of the larval Ae. aegypti rectum identified a particulate coat on the apical lamellae suggesting the presence of portasomes which correspond to the V1 portion of the V ATPase .