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SUMMARYCultured ovine trachea submucosal gland cells release lysozyme in response to extracellular application of secretagogues, including the muscarinic receptor agonist methacholine (20 /LM).Investigation of the ultrastructure has shown that these cells contain electron-dense cored granules, which differ from the intact tissue, but appear to be released in response to the application of methacholine and can be arrested during exocytosis by the application of tannic acid. The release process appears to be linked to electrophysiological events activated by methacholine. Extracellular application of nmethacholine and intracellular photorelease of Ca2+ from DM-nitrophen evoked similar events suggesting that a rise in intracellular Ca2+ may occur following muscarinic receptor activation. Measurements of the reversal potential Land the inhibitory action of the chloride channel blocker niflumic acid (10),UM) indicated that Ca2+ activated Cl channcl activity underlies these events. Some of the cultured submucosal gl.and cells also rcsponded similarly to intracellular photorelease of inositol 1,4,5-trisphosphate, suggesting a possible link between musc.arinic receptor occupation by agonist, release of calcium from stores, and activation of Ca 2'-activated Cl current. Secretion of lysozyme, methacholine-activated currents and currents evoked by intracellular photorelease of Ca2+ \vere also attenuated by the potent bronchodilator Ro 31-6930

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