Exocytosis in living salivary glands : dynamic analysis by video microscopy and confocal microscopy

点击翻译按钮获取中文摘要

Rat parotid acinar cells possess two distinct secretion systems regulated by different receptor-intracellular signalling mechanisms, i.e., enzyme release mediated by the beta-receptor and fluid secretion triggered by the alpha- and muscarinic receptors. Previous light and electron microscopic observations on fixed cells have shown that the exocytosis caused by the beta-agonist results in the enlargement of luminal membrane and its subsequent reduction by endocytosis, whereas the alpha- and muscarinic agonists induce vacuole formation that might arise from the swelling of a part of Golgi apparatus. The observation of living parotid acinar cells with video-enhanced microscopy and confocal microscopy during stimulation with the beta-agonist isoproterenol and the muscarinic agonist carbachol have shown that, contrary to the previous interpretations, isoproterenol evoked exocytosis involving neither the gross enlargement of luminal membrane nor the light microscopically detectable endocytosis. Both of these membrane events were instead observed in cells stimulated with carbachol ; the "vacuoles" formed in these cells were considered mostly as the enlarged lumina. These results indicate that two distinct exocytosis-endocytosis coupling mechanisms exist in the salivary secretion system. The staining of the stimulated cells for F-actin suggested the possible involvement of microfilaments and calcium in the discrimination of these different membrane dynamics.