Fig. 6. Model illustrating the role of membrane transport proteins in pH regulation as well as in H⁺, Na⁺ and K⁺ recycling and amino acid absorption. The localization and colocalizations of H⁺ V-ATPase, AgNAT8, AgNHA1 and Na⁺/K⁺ P-ATPase provide insight into these processes in anterior and posterior midgut cells. The rectum is divided into two functional parts based on the immunolocalization of the transport proteins; postulated interactions between these and yet to be identified proteins are discussed in the text. The shades of pink or orange indicate transport proteins localized in this study; shades of green indicate proteins localized in other studies and white indicates postulated but unidentified proteins. The key points are (1) that H⁺ V-ATPase is basal and Na⁺/K⁺ P-ATPase is apical in anterior midgut, (2) that H⁺ V-ATPase and AgNAT8 constitute a functional NHE (NHE_V-NAT) in the apical membrane of posterior midgut cells, and (3) that AgNHA1 recycles H⁺ in conjunction with H⁺ V-ATPase and recycles Na⁺ in conjunction with AgNAT8 in the apical membrane of posterior midgut cells.