Glycoprotein secretion in vitro by human airway: Normal and chronic bronchitis

Abstract

Precursor uptake, synthesis, and discharge of glycoproteins by mucous and serous cells of submucosal glands and surface epithelial secretory cells (SES cells) of normal and chronic bronchitic human airways were studied in explants of bronchial mucosa maintained in organ culture. Quantitative assessment of precursor incorporation and secretory rate was carried out by autoradiographic analysis of explants pulse-labeled with tritiated sugars or amino acids. Studies of precursor uptake showed that (i) [ 3H]threonine transport into mucous and serous cells was largely ouabain-sensitive, (ii) [ 3H]glucose transport was only partially ouabain-sensitive and was more sensitive in mucous than in serous cells, and (iii) the uptake of neither precursor was markedly ouabain-sensitive in SES cells. Studies of glycoprotein synthesis within mucous, serous, and SES cells showed that, in all three, precursor incorporation into intracellular macromolecules was inhibited to a similar degree by cycloheximide and salicylate. The effects of post-pulse addition of ouabain, cyclo-heximide, and salicylate indicated that precursor uptake, glycoprotein synthesis, and discharge by mucous and serous cells, are not coupled events and that each process is essentially rate-independent. In explants from patients with chronic bronchitis, both threonine uptake and glycoprotein synthesis appeared to occur at a higher rate than in explants from normal subjects.