Figure 5.

Generalized model for transporters on gill ionocytes of Unionidae (Mollusca) based on transporters identified by the present review. A single cell is shown because no studies have identified different ionocyte types. Along the apical membrane are vacuolar-type H⁺-adenosine triphosphatase (ATPase; VHA), apical Na⁺-channel, electrogenic H⁺/2Na⁺ (or Ca²⁺)-exchanger [H2Na(Ca)E], anion/SO₄²⁻-exchanger, epithelial Ca²⁺-channel (ECaC), and anion exchanger. On the basolateral membrane are plasma membrane Ca²⁺-ATPase (PMCA), Na⁺/K⁺-ATPase (NKA), and K⁺-channel (KC). 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.