Dynamic analysis by confocal microscopy of Salivary water secretion

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Secretion mechanism of water by saliary glands was analyzed in living cells by confocal laser scanning microscopy. Tissue slices or dissociated acini were perfused with medium containing various fluorescent probes, and stimulated fluid secretion by adding carbachol. 1) membrane dynamics : The luminal membrane of acinar cells exhibited the long-term (more than 30 min) exocytosis-endocytosis coupling. Scanning and transmission electron microscopy revealed this system to be coated vesicle non-mediated. 2) Tight junction : Fluid-phase tracer dextrans-FITC and membrane marker FM1-43 revealed that dextrans up to MW 10K appeared in the lumen after the secretory stimulation whereas FM1-43 did not stain the luminal membrane, indicating that during fluid secretion tight junction opens its 'gate' but keeps its 'fence' function to remain unchanged. 3) IP3 receptors and Ca signaling Real-time Ca imaging by confocal microscopy exhibited Ca release from the apical cytoplasm of certain duct cells. Immunoelectron microscopy showed the IP3-reactive sites to be localized at the apical vesicles, which are considered newly defined IP3-receptor sites involved in Ca signaling.