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Title: Localization and functional role of synaptotagmin III in insulin secretory vesicles in pancreatic beta-cells. Author: Mizuta M, Kurose T, Miki T, Shoji-Kasai Y, Takahashi M, Seino S, Matsukura S. Journal: Diabetes; 1997 Dec; 46(12):2002-6. PubMed ID: 9392487. Abstract: Pancreatic beta-cells secrete insulin by Ca2+-triggered exocytosis of insulin-containing large dense-core vesicles. Synaptotagmin is a Ca2+/phospholipid-binding protein and is a good candidate for the Ca2+ sensor for exocytosis of synaptic vesicles in neurons. In the present study, we generated a polyclonal antibody against synaptotagmin III, and found that synaptotagmin III immunoreactivity was present at high levels in insulin-containing pancreatic islet cells and insulin-secreting clonal MIN6 cells. In subcellular fractionations of MIN6 cells, synaptotagmin III was recovered in the vesicular fractions containing both insulin and vesicle-associated membrane protein-2 (VAMP-2), but not in synaptophysin-positive fractions. The secretory vesicles immunoprecipitated by anti-VAMP-2 antibody contained synaptotagmin III and insulin. In addition, treatment of streptolysin-O-permeabilized MIN6 cells with anti-synaptotagmin III antibody significantly inhibited Ca2+-triggered insulin secretion. These results indicate that synaptotagmin III is localized in insulin-containing dense-core vesicles in pancreatic beta-cells, and further strongly suggest that synaptotagmin III is the Ca2+ sensor in the exocytosis of insulin secretory vesicles.[Abstract] [Full Text] [Related] [New Search]