Fig. 1. Immunolocalization of P-type Na⁺/K⁺-ATPase (red) and V-type H⁺-ATPase (blue) in the different regions of the midgut of fourth instar A. aegypti larvae. In the whole mounts of gastric caeca (GC; A), the proximal two thirds of each caecum expressed high levels of P-type Na⁺/K⁺-ATPase and the distal third expressed V-type H⁺-ATPase. (B-D) In the paraffin sections of caeca P-type Na⁺/K⁺-ATPase was localized to the basal membrane of the proximal segment only and V-type H⁺-ATPase was on the apical membrane throughout the caecum and also on the basal membrane on the distal caecum. In the very anterior of the midgut, high P-type Na⁺/K⁺-ATPase expression was found in the very anterior region of the midgut (E, white arrow) on the basal membrane (G, white arrow). The apical membrane in this region did not label for either ATPase (G). In the anterior midgut (AMG) there was high V-type H⁺-ATPase expression on the basal membrane (E) and P-type Na⁺/K⁺-ATPase was expressed apically (H). In the posterior midgut (PMG; F) V-type H⁺-ATPase was apically, and P-type Na⁺/K⁺-ATPase basally, expressed. All images were overlays of both Cy3 and Cy5 signals. Scale bars, 100 µm (A,B,E-G), 50 µm (C,D,H,I).