Human neutrophil elastase releases two pools of mucinlike glycoconjugate from tracheal submucosal gland cells

Neutrophil elastase can contribute to the pathogenesis of increased airway reactivity and excess mucus secretion in many pulmonary diseases. Ten nanom olar human neutrophil elastase (HNE) effectively empties airway serous cell s, raising the question of why HNE is not equally effective at emptying muc ous cells of their stored mucin because total release of mucin granules is not seen in postmortem examination of even the most severe disease. To bett er resolve the mucus secretagogue action of HNE, we measured secretion of m ucinlike glycoconjugates (MGCs) released from freshly isolated swine trache al submucosal gland cells in fractions of the superfusate acquired every 2 min. Six to fifty nanomolar HNE released a fixed quantity of MGCs at an inc reasing rate with increasing concentrations of enzyme, an action consistent with the release of cell surface mucinlike molecules. The polycation poly- L-lysine (1 mu g/ml) released a similar transient of MGCs. A steady-state d oubling of MGC rate of release was seen as long as 100 nM HNE was present, but this stimulus represented less than a 1% release of stored MGCs/min and was consistent with release of mucin vesicles from cell stores. Both actio ns of HNE were inhibited by the specific inhibitors L-680833 and DMP-777 bu t not by 30 mu M erythromycin. Therefore, HNE release of MGCs from tracheal submucosal glands is limited by both the fixed quantity of the MGCs in the transient pool and by the small steady-state response to the higher concen trations of enzyme.