New methods used to investigate the control of mucus secretion and ion transport in airways.

Our group developed two in vivo methods to study secretions from submucosal glands in exposed tracheal epithelium. (1) The exposed mucosal surface was coated with powdered tantalum; accumulated secretions produced elevations (hillocks) in the tantalum layer under which the duct openings were located. The rate of formation of the hillocks was observed through a dissecting microscope, and recorded by television on a video tape recorder. (2) Micropipets were used to collect timed samples from individual gland duct openings. With these techniques, the innervation of the submucosal glands and the autonomic regulation of their secretions were studied. We studied the control of ion movement across tracheal epithelium because active ion transport forms local osmotic gradients across epithelia which could regulate transepithelial water movement. We mounted pieces of the posterior wall of dog trachea in Ussing-type chambers and measured unidirectional fluxes of Cl- and Na+ under short-circuit conditions with 36Cl and 24Na. We found active transport of Cl- toward the lumen and Na+ toward the submucosa. With this technique we investigated the effect of parasympathomimetic drugs on ion movement. With a new in vitro method we studied output of 35S bound to sulfated mucins and movement of ions in cat trachea. We mounted pieces of anterior tracheal wall in Ussing-type chambers, added sodium 35S-sulfate to the submucosal side and monitored secretion of bound 35S in samples from the luminal side after dialysis. The unidirectional fluxes of Cl- and Na+ were measured with 36Cl and 22Na. With this method we examined the effect of alpha-adrenergic and beta-adrenergic agonists on mucin secretion and ion movement. Also with this preparation we studied the relationship between the permeability of the paracellular pathway to 14C-sucrose and the pattern of tight junction strands.