Mucus glycoconjugate secretion in cool and hypertonic solutions

For sensitive individuals, exercise-induced asthma is triggered by cold and dry air and is often accompanied by a productive cough. In this study, we determined whether cold solutions and/or solutions of increased tonicity directly caused an increase in glycoconjugate (GC) secretion. To test this, we used isolated swine tracheal submucosal gland cells (TSGCs) and measured the rate of GC secretion at 37 and 32 degrees C in isotonic solutions and in solutions made hypertonic by 30 mosM. TSGCs were isolated under conditions that minimized the rate of GC secretion and were perfused with medium 199 equilibrated with 5% CO2 to a pH of 7.4. A lectin-based assay was used to specifically detect GC present in each 2-min fraction of the perfusate. Basal secretion was 3.1-fold greater at 32 degrees C (n = 3) than at 37 degrees C (n = 4; P < 0.05). At 37 degrees C, increasing perfusate osmolarity by 30 mosM increased the average rate of secretion by 41 +/- 11% (n = 4; P < 0.05); return to isotonic perfusate caused a 4.5 +/- 1.8-fold transient increase in secretion(n = 4; P < 0.05) that was complete within 10 min. At 32 degrees C, changing tonicity of the perfusate had no significant effect but returning to isotonic perfusate caused a 2.3 +/- 0.7-fold transient increase in secretion (n = 3; P < 0.05). Thus key stimuli that trigger obstruction of airflow (cold and increased osmolarity) can also directly stimulate GC secretion in the airway. Such increased secretions may contribute to the productive cough observed in some individuals in response to cold air.