Electrolyte and other chemical concentrations in tracheal airway surface liquid and mucus

With the ferret in vitro tracheal preparation, we measured the electrolyte and chemical composition of airway surface liquid (ASL) under control conditions and when drugs were added to promote submucosal gland secretion and to change epithelial ion transport. Control ASL was hyperosmolar (342 +/- 2.8 mosmol/kg) compared with ferret plasma and surrounding buffer. Higher values were also found for sodium (167 +/- 1.7 mmol/l), potassium (9.0 +/- 0.05 mmol/l), total calcium (3.46 +/- 0.11 mmol/l), and ionized calcium (2.55 +/- 0.18 mmol/l). pH was lower (7.12 +/- 0.03) than in plasma or buffer. Addition of methacholine to the surrounding buffer increased flow of ASL and potential difference across the mucosa and lowered pH, calcium, sodium, and chloride concentrations. Potassium concentration was increased. Phenylephrine increased flow and decreased calcium concentrations. Salbutamol (albuterol) had no effect on flow but decreased pH and increased calcium and potassium concentrations. Histamine increased flow and calcium concentrations and decreased pH. These changes are presumably due to changes in gland secretion and epithelial transport. Methacholine and phenylephrine increased the sugar content of the secretions, the changes with phenylephrine being larger. Thus resting ASL is hyperosmolar and relatively acid, with high cation contents, and administration of drugs changes its composition by actions on submucosal glands and epithelium.