ELECTROPHYSIOLOGICAL AND ULTRASTRUCTURAL EVENTS EVOKED BY METHACHOLINE AND INTRACELLULAR PHOTOLYSIS OF CAGED COMPOUNDS IN CULTURED OVINE TRACHEA SUBMUCOSAL GLAND-CELLS

Cultured ovine trachea submucosal gland cells release lysozyme in resp onse to extracellular application of secretagogues, including the musc arinic receptor agonist methacholine (20 mu M). Investigation of the u ltrastructure has shown that these cells contain electron-dense cored granules, which differ from the intact tissue, but appear to be releas ed in response to the application of methacholine and can be arrested during exocytosis by the application of tannic acid. The release proce ss appears to be linked to electrophysiological events activated by me thacholine. Extracellular application of methacholine and intracellula r photorelease of Ca2+ from DM-nitrophen evoked similar events suggest ing that a rise in intracellular Ca2+ may occur following muscarinic r eceptor activation. Measurements of the reversal potential and the inh ibitory action of the chloride channel blocker niflumic acid (10 mu M) indicated that Ca2+-activated Cl- channel activity underlies these ev ents. Some of the cultured submucosal gland cells also responded simil arly to intracellular photorelease of inositol 1,4,5-trisphosphate, su ggesting a possible link between muscarinic receptor occupation by ago nist, release of calcium from stores, and activation of Ca2+-activated Cl- current. Secretion of lysozyme, methacholine-activated currents a nd currents evoked by intracellular photorelease of Ca2+ were also att enuated by the potent bronchodilator Ro 31-6930 (1 mu M). We conclude that Ca2+-activated Cl- conductances play an important role in secreto ry processes in cultured submucosal gland cells. This may have a beari ng on both physiological control of secretory events and regulation of the nature of airway surface liquid, Ca2+-activated Cl- channels may offer a potential target site for novel therapeutic agents.