Figure 4.

Generalized model for transporters on epithelial ionocytes of aquatic insects based on transporters identified by the present review. A single cell is shown because no studies have identified different ionocyte types, although research with mosquito larvae suggests that transporters for at least K⁺ and Ca²⁺ are not collocated with those for Na⁺ and Cl⁻ on the anal papillae. Also, the evidence suggests variation among aquatic insect orders. Along the apical membrane are vacuolar-type H⁺-adenosine triphosphatase (ATPase; VHA), apical Na⁺-channel, Na⁺/H⁺-exchanger (NHE), epithelial Ca²⁺-channel (ECaC), and anion exchanger (AE). On the basolateral membrane are Na⁺/K⁺-ATPase (NKA). K⁺-channel (KC), Na⁺/Ca²⁺-exchanger (NCX), and plasma membrane Ca²⁺-ATPase (PMCA). Dashed arrows indicate diffusion, whereas solid arrows indicate active transport. Arrows that split indicate reactions. CA2=carbonic anhydrase type 2 enzyme; ATP=adenosine triphosphate; ADP=adenosine diphosphate.