Ion transport in cultured pig tracheal submucosal gland acinar cells studied by X-ray microanalysis

The submucosal glands of the airway may contribute more to the airway fluid than the surface epithelium. The cellular mechanisms underlying the regulation of electrolyte and water transport in airway submucosal glands are, however, still poorly understood. Therefore, we attempted to establish a cell culture system to facilitate study of this regulation. Acinar cells were isolated by enzymatic disaggregation from pig tracheal submucosal tissue and cultured on a plastic substrate coated with human placental collagen. The fine structure of the cells in confluent culture was studied by conventional transmission electron microscopy. The elemental content in resting cells and stimulated cells grown on a permeable substrate was studied by X-ray microanalysis. The cultured cells retained structural characteristics (microvilli, secretory granules and desmosomes) of in situ epithelia. The total intracellular Cl and K concentrations significantly decreased after stimulation with the cholinergic agonist acetylcholine, the predominantly alpha-adrenergic agonist norepinephrine, or the beta-adrenergic agonist isoproterenol. Both ionomycin and 8-bromoadenosine 3':5'-cyclic monophosphate (8-bromo-cAMP) caused a marked decrease of the intracellular Cl, K and Na concentrations. Cl- secretion induced by acetylcholine was inhibited by Cl- channel blockers anthracene-9-carboxylic acid and 5-nitro-2-(3-phenylpropyl-amino)-benzoic acid (NPPB), but Cl- efflux induced by 8-bromo-cAMP was blocked only by NPPB. The intracellular Cl and Na content significantly increased and the cellular K content markedly decreased after treatment with ouabain. These results indicate that the cultured acinar cells maintained the structural and functional characteristics of in situ tissue and that this system is suitable for studying aspects of ion and water transport by the airway submucosal gland cells.