FIGURE 1.

Cell types and transporters in the cortical collecting duct (CCD). Intercalated and principal cell ion transporter distribution within of the CCD is shown. In type B intercalated cells (ICs), the Na⁺-dependent Cl⁻/HCO₃⁻ exchanger, NDCBE, mediates Na⁺ and HCO₃⁻ absorption, whereas pendrin mediates HCO₃⁻ secretion and Cl⁻ absorption. Through the action of these 2 transporters, Cl⁻ and HCO₃⁻ are recycled across the apical membrane. Net H⁺ and Cl⁻ exit occur across the basolateral plasma membrane through the Cl⁻ channel, ClC-K2, and the H⁺-ATPase. Na⁺ exits the cell through the Na⁺-HCO₃⁻ cotransporter, AE4. Type A ICs secrete H⁺ through the apical plasma membrane H⁺-ATPase with net HCO₃⁻ efflux across the basolateral plasma membrane through the Cl⁻/HCO₃⁻ exchanger, AE1. Type A ICs also express the ammonia channel, Rhbg, in the basolateral regions of the cell. Principal cells absorb Na⁺ through the epithelial Na⁺ channel, ENaC, which exits across the basolateral plasma membrane through the Na⁺-K⁺-ATPase. In so doing, it generates a lumen-negative transepithelial voltage, which provides the driving force for net secretion of K⁺. Most likely, Cl⁻ is also absorbed through paracellular transport driven by the lumen-negative transepithelial voltage generated by the epithelial Na⁺ channel, ENaC. Non-A, non-B ICs are rare in mouse CCD. However, these cells express pendrin and the H⁺-ATPase on the apical plasma membrane and express ClC-K2, AE4, and Rhbg in the basolateral regions of the cell. Whether these cells express NDCBE is unclear.