Osmolality affects ion and water fluxes and secretion in the ferret trachea

Abstract

Nonisosmolar solutions were placed in the lumen of the ferret trachea in vitro in an organ bath. Hyposmolar (150 mmol/kg) solutions progressively increased in osmolarity over 1 h. Increases in luminal concentration of impermeant blue dextran occurred only after 5 min, suggesting that the initial changes were due to ion rather than water fluxes. With hyperosmolar solutions the osmolarity decreased over 1 h with no change in blue dextran concentration, indicating that ion but not water fluxes were taking place. Cooling the preparation to 4 degrees C greatly reduced the osmolaity changes with hyperosmolar solutions and halved those with hyposmolar solutions, suggesting that active ion transport was involved. Hyposmolar (75–150 mmol/kg) and hyperosmolar (450–900 mmol/kg) solutions both increased albumin output into the lumen, but the response was prevented by cooling the trachea to 4 degrees C. Hyposmolar and hyperosmolar solutions both increased the output of lysozyme from glandular serous cells into the lumen. The response to hyposmolar solutions was stronger. Cooling the trachea abolished the lysozyme response to hyperosmolar solutions. Thus hypo- and hyperosmolar solutions promote ion transport in directions to restore isosmolarity. Both nonisosmolar solutions promote albumin movement by active transport across the mucosa and lysozyme secretion from submucosal glands, responses inhibited by tracheal cooling and therefore dependent on metabolically active processes.