Airway surface liquid hydration and osmotic regulation

Airway surface liquid hydration and its osmotic regulation refer to the physiological processes that control the volume and composition of fluid covering airway epithelia. This thin layer—composed primarily of water, ions, proteins, mucins, and antimicrobial factors—is essential for effective mucociliary clearance. The balance is maintained by active transepithelial ion transport involving chloride secretion via CFTR and other anion channels; sodium absorption via ENaC; potassium fluxes; bicarbonate secretion; aquaporin-mediated water permeability; as well as regulatory input from purinergic signaling pathways. Disruption in these mechanisms leads to diseases such as cystic fibrosis where dehydrated mucus impairs cilia function resulting in chronic infection. While this is a critical therapeutic axis in respiratory medicine—especially for diseases like cystic fibrosis—it is not itself a discrete molecular target but rather an emergent property regulated by multiple molecular targets.

Other names

Mucus hydrationAirway surface liquid (ASL) homeostasisASL hydrationMucociliary clearance (in context)Osmotic effect on airway surface liquid

Mechanisms relate to modulation of epithelial ion transport to restore or maintain proper ASL volume/hydration, including: - Activation or potentiation of chloride secretion via CFTR or CaCCs increases water movement into the ASL by osmosis. - Inhibition of sodium absorption via ENaC reduces water reabsorption from the ASL. - Modulation of purinergic signaling regulates both Cl− secretion and Na+ absorption through G protein-coupled receptors.