Sequential-replenishment mechanism of exocytosis in pancreatic acini

T Nemoto, R Kimura, K Ito, A Tachikawa… - Nature cell …, 2001 - nature.com
T Nemoto, R Kimura, K Ito, A Tachikawa, Y Miyashita, M Iino, H Kasai
Nature cell biology, 2001nature.com
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 μM. Zymogen granules fused
with the plasma membrane maintain their Ω-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 …
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 μM. Zymogen granules fused with the plasma membrane maintain their Ω-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.
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