| Co-Investigator(Kenkyū-buntansha) |
SHIN Sunok School of Dentistry, Assistant Prof., 歯学部, 助手 (30226336)
KAMIYA Masako School of Dentistry, Assistant Prof., 歯学部, 助手 (80181907)
YASHIRO Koji School of Dentistry, Lecturer, 歯学部, 講師 (50182316)
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| Research Abstract |
It is very important to clarify the mechanism of secretion in the animal, in order to know how to communicate and regulate between both cells, and tissues. Exocytosis is the final stage of the stimulus-secretion coupling phenomenon which is linked to the membrane fusion between secretory granules and plasma membranes. In this study, the rat parotid gland cells were used as a model for secretory cells. A cell-free exocytosis system, reconstituted with isolated secretory granules and isolated apical plasma membranes was adopted to study the molecular mechanism of the final step of secretion. In this system, the indicators of the exocytosis were amylase release and the membrane fusion which was assayd by fluorescence dequenching. Consequently, the metabolites (free fatty acids, 1,2-diacyl-sn-glycerol, phosphatidic acid) from membrane phospholipids accelerated both the amylase release and membrane fusion. According to the analysis of the localization of phospholipid hydrolyzing enzymes, it
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was suggested that the metabolites were generated in the membrane region of particular organelles. These results show the existence of specific membrane sites and mechanisms for exocytosis. It was known that the activity of phospholipases A_2 and D was regulated by trimmer-type, and low molecular GTP-binding proteins (G-protein), respectively. The analysis found that the localization of both G-proteins in plasma membranes and in secretory granules was different. The question of how the metabolizing enzyme and G-protein regulate the exocytosis remains to be answered. It was also observed that the proteins of cytoskeleton were bound to plasma membranes, not to secretory granule membranes, and that they suppressed the amylase release and the membrane fusion in the cell-free system.
From the aforementioned, we can find the mechanism which decides the region where the exocytosis occurs, and parts of the regulatory mechanisms used in the acceleration and suppression of exocytosis at the molecular level. Less
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