Figure 1: Intercalated and principal cells transporters and channels within the cortical collecting duct:

Type B ICs absorb NaCl through pendrin-mediated apical Cl⁻ /HCO₃⁻ and the Na⁺-dependent Cl⁻/HCO₃⁻ exchanger, NDCBE, acting in tandem. Pendrin and the CFTR Cl⁻ channel mediate HCO₃⁻ secretion, while they recycle Cl⁻ across the apical plasma membrane. H⁺ and Cl⁻ exit the cell through the basolateral plasma membrane ClC-K2 Cl⁻ channel and the H⁺-ATPase, while the basolateral membrane Na⁺-HCO₃⁻ cotransporter, AE4, and the Na,K-ATPase mediate Na⁺ exit. In type A ICs the apical membrane H⁺-ATPase and the basolateral membrane Cl⁻/HCO₃⁻ exchanger, AE1, act in series to mediate H⁺ secretion. Principal cells absorb Na⁺ through the apical membrane epithelial Na⁺ channel, ENaC, which generates the lumen-negative transepithelial voltage, providing the driving force for K⁺ secretion through K⁺ channels such as ROMK and Maxi K⁺ channels.