Fig. 6.

Basic overview of the epithelial response to water loss from the airway surface liquid. As ventilation increases, water is lost from the airway surface liquid, resulting in transient hyperosmolarity and the passive movement of water from airway epithelial cells (arrows) to restore the osmolarity of the airway surface liquid. The movement of water causes epithelial cells to shrink and initiates cellular signaling events, including an increase in intracellular calcium (Ca²⁺). The addition of osmotically active substances such as mannitol and hypertonic saline similarly cause water movement to restore the surface osmolarity.