Figure 8.

The hypothetical role of pendrin in the regulation of airway surface liquid (ASL). (A) Pendrin regulates ASL volume via Cl⁻ and subsequent water absorption. The secreted HCO₃⁻ will evaporate, thus leading to net anion movement into the cells. Under inflammatory conditions, upregulated pendrin compensates for the over-secreted fluid by upregulated ANO-1 channels. (B) In pendrin-deficient airways, ASL thickness is increased due to the lack of Cl⁻ absorption by pendrin under basal conditions and cannot compensate for the over-accumulated fluid.