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Sequential-replenishment mechanism of exocytosis in pancreatic acini

Nature Cell Biology volume 3, pages 253–258 (2001)Cite this article

Abstract

Here we report exocytosis of zymogen granules, as examined by multiphoton excitation imaging in intact pancreatic acini. Cholecystokinin induces Ca2+ oscillations that trigger exocytosis when the cytosolic Ca2+ 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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Figure 1: Exocytosis and [Ca2+]i at low CCK concentration.
Figure 2: Exocytosis and [Ca2+]i at a high CCK concentration.
Figure 3: CCK-dependence and lifetime of Ω-shaped profiles.
Figure 4: Diameters of zymogen granules and SRB-filled structures.
Figure 5: Sequential exocytosis of zymogen granules.
Figure 6: Sequential-replenishment mechanism of exocytosis.

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Acknowledgements

This work was supported by Core Research for Evolutional Science and Technology (CREST) of the Japan Science and Technology Corporation (JST), and by the Research for the Future program of the Japan Society for the Promotion of Science (JSPS), of which K.I. is a research fellow.

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Authors and Affiliations

  1. Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585, Japan

    Tomomi Nemoto, Ryoichi Kimura & Haruo Kasai

  2. University of Tokyo School of Medicine, Hongo, Bunkyo-ku, 113-0033, Tokyo, Japan

    Tomomi Nemoto, Ryoichi Kimura, Koichi Ito, Akira Tachikawa, Yasushi Miyashita & Masamitsu Iino

  3. CREST, Japan Science and Technology Corporation, Hongo , Bunkyo-ku, 113-0033, Tokyo, Japan

    Tomomi Nemoto, Akira Tachikawa, Masamitsu Iino & Haruo Kasai

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Correspondence to Haruo Kasai.

Supplementary information

Figure S1

Comparison of depth penetration between two-photon excitation imaging and confocal imaging. a, b, Images of an acinar preparation stained with Oregon green 488 BAPTA-1-AM, acquired by x–z scanning with two-photon laser-scanning microscopy (a) or confocal laser-scanning microscopy (b). Luminal structures are apparent in the two-photon excitation image, but not in the confocal image. Confocal imaging (Fig. 1b, d) was carried out using the same scanning microscope and objective lens, but an argon laser was used for excitation at 488 nm and fluorescence of Oregon green 488 BAPTA-1 was measured at 500–600 nm through a pinhole (Olympus, CA2). c, Stereo-pair of two-photon images, obtained by xndash;yndash;z scanning of an acinar preparation that had been immersed in 0.5 mM SRB for 20 min and stimulated with 10 pM CCK for 5 min. Many W-shaped profiles of fused zymogen granules are visible adjacent to lumens, but not to basolateral membranes. (PDF 285 kb)

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Nemoto, T., Kimura, R., Ito, K. et al. Sequential-replenishment mechanism of exocytosis in pancreatic acini . Nat Cell Biol 3, 253–258 (2001). https://doi.org/10.1038/35060042

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