AQP5

Aquaporin 5 (AQP5) is a water channel protein encoded by the AQP5 gene in humans. It belongs to the aquaporin family of integral membrane proteins that facilitate rapid, selective movement of water across cell membranes in response to osmotic gradients. Each AQP5 monomer forms a water pore, and four monomers assemble as a tetramer in the plasma membrane.

AQP5 is expressed in tissues involved in fluid secretion and airway function. Its prominent expression is in secretory glands such as the salivary and lacrimal glands, and in respiratory epithelia including airway lining and alveolar type I pneumocytes. The exact distribution can vary among tissues and species, but these sites are consistently highlighted in reports.

Functionally, AQP5 mediates transepithelial water transport and contributes to water movement during the secretion of saliva and tears, as well as to airway surface liquid homeostasis. Regulation of AQP5 activity involves trafficking to the apical membrane; secretagogues and physiological stimuli can promote its membrane insertion, enhancing water permeability when secretion is required.

In research and clinical contexts, AQP5 is studied for its role in glandular fluid secretion and respiratory tract hydration. Animal models lacking AQP5 often show reduced saliva and tear secretion, underscoring its contribution to secretory processes. Ongoing studies continue to clarify its regulation, tissue-specific functions, and potential implications in glandular or pulmonary disorders.