Immunocytochemical study of trans-Golgi-network (TGN)-associated protein in salivary acinar cells under varying condition of salivary secretion

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Specific antisera against Rab3A, Rab3B, Rab3D, Rab4, and Rab6, small CTP-binding proteins, and TGN38, a marker of trans-Golgi network (TGN), have been used to examine the distribution of these Rab proteins in several endocrine and exocrine glands of mouse and rat by immunofluorescence method. The anti-Rab3A and Rab6 immunostained some rat pituitary endocrine cells, It is conceivable by these distribution that the Rab3A-immunoreactive cells may be ACTH cells. The anti-Rab3A immunostained exclusively several endocrine cells of pancreatic islets of rat. When cosecutive sections were immunostained with antibodies against pancreatic hormones, these immunostained cells were found to be alpha cells. In contrast, anti-Rab3D immunostained pancreatic acinar cells, and the immunoreacted region localized to the zymogen granule field. Double electron microscopic immunogold localizations for Rab3A or Rab3D and TGN38 have been tried in these materials, but no optimal resolution has not obtained by electron microscope. However, it was found in the light microscopy that these immunoreactive localization of Rab proteins should be in the field of secretion granules. Because of the Rab associated with secretion granules, Rab proteins may play a role in regulated exocytosis.