This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cation-Proton Antiporters (CPAs) are a new group of pH regulating transporter that have recently been cloned and localized to specific regions of the mosquito alimentary canal. No functional characterization has been performed for these mosquito transporters and their function has only been inferred from sequence homology, 2H+ are thought to enter the cell in exchange for efflux of 1 Na+. One of the cloned sequences, AgNHA1, has been setup to be expressed in the Xenopus oocyte heterologous expression system. As the ions are exiting the oocytes it is very difficult to identify exactly which cations are passing out through the plasma membrane. The current hypothesis is that it could be either Na+ or K+. We have performed preliminary flux measurements for Na+ in support of a grant submission.