| Research Abstract |
To study a coupling mechanism between fluid secretion and exocytosis. the major salivary glands were examined physiologically and morphologically as a model to produce a macroscopic secretion with various concentration of protein.
A.Secretory time course : The parotid and submandibular glands were used as models of serous and seromucous secretion, respectively. The secretory time course of amylase and mucin was similar, a single muscarinic stimulation induced an initial burst of protein secretion followed by low sustained level of secretion, Overloading of β-adrenergic stimulation increased the protein secretion followed by high secretion level. Fluid secretion was induced by mainly muscarinic stimulation, but a minimal by β-adrenergic stimulation. During weak muscarinic stimulation, the fluid secretion was potentiated by β-adrenergic stimulation. This suggests that the upregulation of transporters by cyclic AMP could be limited by metabolic energy supply and excess cytosolic Ca^<2+>
B.M
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orphology : Morphological change of the perfused whole parotid gland was examined by electron microscope along secretory time course. A single carbachol stimulation caused an initial transient enlargement of intercellular canalliculi (IC). Combined stimulation of carbachol and isoproterenol induced a vigorous exocytosis on IC.Either stimulation a) reduced the number of microvilli, b) enlarge the rER.suggesting activation of Ca^<2+> metabolism, and c) increased electron density of mitochondria, related to the increase of oxygen consumption. Confocal laser microscope revealed that the paracellular route of secretion is controlled by secretory stimulation, and that the transcellular fluid secretion is dominant at initial secretory phase.
C.Molecular machinary for exocytosis : In the parotid gland VAMP-2 was identified on the secretory granule membrane, syntaxin4 and SNAP23 were located on the luminar membrane. Whereas, syntaxin 1A was localized at acinar cells of the lingual glands. This suggests that there is some differnce in exocytotic mechanism between mucinous and serous secretion.
D.Dynamics of secretory molecules : The size of molecular filter across the paracellular route was estimated from the saliva/perfusate ration of various size of labelled dextran during secretion by muscarinic stimulation, as 5A.Anionic dependency of fluid secretion was examined precisely in the buccal gland of sheep.
Thus the project revealed above new findings to show that combination of intracellular signals enables coupling between fluid secretion and exocytosis at various aspects. Less
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