Purinergic and Cholinergic Agonists Induce Exocytosis from the Same Granule Pool in HT29-Cl.16E Monolayers

Several secretagogues induce mucin secretion in epithelial monolayers, as determined by measuring released granule contents. To assess whether different agonists act on the same granule pool, capacitance changes in intact monolayers of the goblet cell line HT29-Cl.16E were measured by a novel impedance method. Apical ATP (purinergic agonist) and basolateral carbachol (cholinergic agonist) induce rapid exocytosis with maximal capacitance changes within 3 min. The maximal levels of exocytosis that can be induced by optimal concentrations of either agonist are the same and produce a 30-40% increase in total monolayer capacitance. When ATP and carbachol are applied simultaneously, the magnitude of exocytosis is unchanged from the single-secretagogue level. The recovery of capacitance to baseline (endocytosis) is significantly faster after ATP stimulation than after carbachol stimulation. When ATP and carbachol are applied sequentially at doses that give maximal exocytosis, the magnitude of the capacitance increase produced by the second secretagogue is less than or equal to that of the capacitance decrease during the recovery period. Together, these data suggest that purinergic and cholinergic agonists act on the same granule pool.