Figure 1.

Ion transport and pharmacologic manipulation in airway epithelium. Transepithelial Na⁺ reabsorption mediated by concerted activity of apical epithelial Na⁺ channels (ENaC: Blocker = Amiloride) and the basolateral Na⁺/K⁺ ATPase. Apical located sodium dependent vitamin C transporter might also contribute to Na⁺ reabsorption. In addition to Na⁺ reabsorption airway, epithelia display a prominent apical Cl⁻ secretion that is mainly mediated by the cystic fibrosis transmembrane conductance regulator (CFTR) in humans and to a lesser extent by Ca²⁺-dependent Cl⁻ channels (CaCC) such as the TMEM channels. This secretion is kept up by the basolateral Na⁺/K⁺/2Cl⁻ cotransporter (NKCC). In the basolateral membrane, several voltage-dependent K⁺ channels have been identified.