Article abstract
Nature Cell Biology 3, 253 - 258 (2001)
Published online: 7 February 2001 | doi:10.1038/35060042
Sequential-replenishment mechanism of exocytosis in pancreatic acini
Tomomi Nemoto1,2,3, Ryoichi Kimura1,2, Koichi Ito2, Akira Tachikawa2,3, Yasushi Miyashita2, Masamitsu Iino2,3 & Haruo Kasai1,3
Abstract
Here we report exocytosis of zymogen granules, as examined by multiphoton excitation imaging in intact pancreatic acini. Cholecystokinin induces Ca 2+ oscillations that trigger exocytosis when the cytosolic Ca 2+ concentration exceeds 1 
M. Zymogen granules fused with the plasma membrane maintain their 
-shaped profile for an average of 220 s and serve as targets for sequential fusion of granules that are located within deeper layers of the cell. This secondary exocytosis occurrs as rapidly as the primary exocytosis and accounts for most exocytotic events. Granule–granule fusion does not seem to precede primary exocytosis, indicating that secondary fusion events may require a plasma-membrane factor. This sequential-replenishment mechanism of exocytosis allows the cell to take advantage of a large supply of fusion-ready granules without needing to transport them to the plasma membrane.
- Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki 444-8585, Japan
- University of Tokyo School of Medicine, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
- CREST, Japan Science and Technology Corporation, Hongo , Bunkyo-ku, Tokyo 113-0033, Japan
Correspondence to: Haruo Kasai1,3 e-mail: hkasai@nips.ac.jp
