As mentioned above and discussed in greater detail in , the hyperpolarizing action of V ATPase can be used to drive many ion transporting processes against an otherwise unfavorable concentration gradient. We hypothesize that the V ATPase on the apical lamellae of the PR in Oc. taeniorhynchus and in the non DAR cells in An. albimanus, is energizing one or more transporters also present on this membrane to translocate ions from the cells to the lumen in order to excrete excess ions from the hemolymph. The ability for An. albimanus larvae to shift Na K ATPase protein localization in response to salinity, as well as the reversibility of this event, may be dependent on the larval stage at which exposure occurs. Younger larvae reared in freshwater and exposed to 25% ASW exhibited a shift in Na K ATPase localization from non DAR to DAR cells in as little as 24 hours. More mature larvae exposed to 25% ASW for 24 hours expressed Na K ATPase in both non DAR cells and DAR cells as if in an intermediate state between freshwater and saline water protein expression. After 48 hours, the majority of Na K ATPase was expressed in the DAR cells of 4th instar larvae.
This could indicate that early instar larvae are far more plastic in terms of regulating gene and or protein expression than late larvae. Slightly different results were obtained when rearing larvae in 25% ASW and exposing them to freshwater. Iressa Whereas 2nd instar larvae shifted Na K ATPase localization from the DAR to non DAR cells within 24 hours of exposure to freshwater, 3rd and 4th instar larvae consistently expressed the protein in both DAR and non DAR cells even after 72 and 48 hours respectively. This may indicate that at the 2nd instar larval stages, Na K ATPase protein shift is fully reversible, whereas more mature larvae cannot downregulate Na K ATPase expression in the DAR cells within the period of time observed. It is possible that the concentration of ASW was too low to cause a complete shift in localization in more mature larvae, and that larvae would respond differently if reared in 50% ASW versus 25% ASW. It is interesting that a protein shift is seen at all in 25% ASW , as the osmolarity is less than that of the An.
albimanus hemolymph . This may be due to the abruptness of the salinity change, with larvae being transferred directly from freshwater to 25% ASW in the present study. Additionally, it could indicate that some event signals the rectum SRC Inhibitor selleck to shift Na K ATPase protein before it is actually necessary to produce a hyper osmotic urine, as if in preparation. CA9 is involved in CO2 excretion CA9 consistently localized to the DAR cells of all anopheline mosquitoes examined , as well as to the AR of Oc. taeniorhynchus regardless of rearing water salinity. Members of the CA family are implicated in both ion and pH regulation in a number of organisms and catalyze the hydration of CO2 to H2CO3 which instantaneously dissociates into H and HCO3 .