Modeling ion transport in the type B intercalated cells. (A) Ion transporter model used for simulations (see Materials and methods). Type B intercalated cells secrete HCO₃⁻ into the lumen by the apical Cl⁻/HCO₃⁻ exchanger pendrin coupled to the basolateral efflux of protons by the V-ATPase and of Cl⁻ by the ClC-K2/Barttin channel. Electroneutral NaCl reabsorption is mediated by the apical coupling of pendrin with the Na⁺-driven Cl⁻/HCO₃⁻ exchanger NDCBE and by the basolateral extrusion of Na⁺ by Na⁺-HCO₃⁻ cotransporter AE4, and of Cl⁻ by ClC-K2. (B) Predicted effects of variations in basolateral membrane chloride conductance (gClC-K) on net fluxes of Cl⁻ through ClC-K2 (blue), of Na⁺ through NDCBE (red), and of apical HCO₃⁻ (black; left) and on net transcellular Na⁺, Cl⁻, and HCO₃⁻ transport (right). The labels 1–3 correspond to relative gClC-K values of 0, 0.15, and 1, respectively.