Cited by 211Pancreatic function and diabetesCellular transport and secretionCalcium signaling and nucleotide metabolism

Imaging analysis reveals mechanistic differences between first- and second-phase insulin exocytosis

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Ohara-Imaizumi, Mica, Fujiwara, Tomonori, Nakamichi, Yoko, Okamura, Tadashi, Akimoto, Yoshihiro, Kawai, Junko, Matsushima, Satsuki, Kawakami, Hayato +3 more·2007·The Journal of Cell Biology

Abstract

The mechanism of glucose-induced biphasic insulin release is unknown. We used total internal reflection fluorescence (TIRF) imaging analysis to reveal the process of first- and second-phase insulin exocytosis in pancreatic β cells. This analysis showed that previously docked insulin granules fused at the site of syntaxin (Synt)1A clusters during the first phase; however, the newcomers fused during the second phase external to the Synt1A clusters. To reveal the function of Synt1A in phasic insulin exocytosis, we generated Synt1A-knockout (Synt1A−/−) mice. Synt1A−/− β cells showed fewer previously docked granules with no fusion during the first phase; second-phase fusion from newcomers was preserved. Rescue experiments restoring Synt1A expression demonstrated restoration of granule docking status and fusion events. Inhibition of other syntaxins, Synt3 and Synt4, did not affect second-phase insulin exocytosis. We conclude that the first phase is Synt1A dependent but the second phase is not. This indicates that the two phases of insulin exocytosis differ spatially and mechanistically.

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  • There is general agreement that many docked granules are released in response to membrane depolarization produced by sulfonylureas or high [K+]o.

    “There is general agreement that many docked granules are released in response to membrane depolarization produced by sulfonylureas or high [K+]o (288, 446, 487, 617).”

    From Pancreatic β-Cell Electrical Activity and Insulin Secretion: Of Mice and Men (2018) · cites this paper as [487]

    The Introduction (page unavailable) says high KCl causes membrane depolarization and can evoke first-phase insulin release. The Results (page unavailable) report that about 75% of first-phase granule fusion under glucose stimulation came from previously docked granules. Our copy does not address sulfonylureas or directly show that high KCl releases docked granules, so it supports the general mechanism but not both specified stimuli. (LLM, conf=0.84)

    Experimental — accuracy not yet measured
  • Stx1a deficiency results in a marked reduction of docked granules and strong suppression of 1st phase insulin secretion, but 2nd phase secretion is unaffected.

    “In one study where TIRF microscopy was used to monitor granule exocytosis, Stx1a deficiency resulted in a marked reduction of docked granules and strong suppression of 1st phase insulin secretion (487). However, 2nd phase secretion was unaffected.”

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Research works printed but not linked: 2

  1. Cerasi, E. 1994 Aetiology of type II diabetes. In Insulin-Molecular Biology to Pathology. F.M. Ashcroft and S.J.H. Ashcroft, editors. IRL Press, Oxford, England. 352–392.
  2. Ohara-Imaizumi, M., T. Ohtsuka, S. Matsushima, Y. Akimoto, C. Nishiwaki, Y. Nakamichi, T. Kikuta, S. Nagai, H. Kawakami, T. Watanabe, and S. Nagamatsu. 2005. ELKS, a protein structurally related to the active zone-associated protein CAST, is expressed in pancreatic beta cells and functions in insulin exocytosis: interaction of ELKS with exocytotic microscopy. Mol. Biol. Cell. 16: 3289–3300. 15888548 PMC1165411

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Authors
Ohara-Imaizumi, M., Fujiwara, T., Nakamichi, Y., Okamura, T., Akimoto, Y., Kawai, J., Matsushima, S., Kawakami, H., Watanabe, T., Akagawa, K., & Nagamatsu, S.
Affiliations
  • 1Department of Biochemistry
  • 2Department of Cell Physiology
  • 5Division of Animal Models, Department of Infectious Diseases, Research Institute, International Medical Center of Japan, Tokyo 162-8655, Japan
  • 3Department of Anatomy,
  • Juntendo University (JP)
  • Kyorin University (JP)
Corresponding author
Nagamatsu, Shinya
Venue
The Journal of Cell Biology
Published
2007-05-14
Volume
177
Issue
4
Pages
695-705
ISSN
  • 0021-9525 (ISSN-L)
  • 1540-8140
OpenAlex
W2124167615
Cited by
211
References
46
Citations by year
2026: 2 · 2025: 6 · 2024: 4 · 2023: 9 · 2022: 7 · 2021: 10 · 2020: 6 · 2019: 7 · 2018: 6 · 2017: 13 · 2016: 5 · 2015: 11 · 2014: 16 · 2013: 10 · 2012: 23
FWCI
18.64
Type
journal article
Language
en
Open access
Licence
cc-by-nc-sa
Locations
  • The Journal of Cell Biology (publishedVersion)
  • PubMed Central (publishedVersion, cc-by-nc-sa)
  • PubMed (publishedVersion)
Topics
  • Health Sciences › Medicine › Surgery › Pancreatic function and diabetes
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Cellular transport and secretion
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Physiology › Calcium signaling and nucleotide metabolism
Keywords
insulin exocytosis, first-phase insulin secretion, second-phase insulin secretion, syntaxin 1A, syntaxin 3, syntaxin 4, granule fusion, pancreatic beta cells, glucose-induced insulin release
MeSH terms
Insulin Secretion, Animals, Cells, Cultured, Exocytosis, Insulin, Islets of Langerhans, Male, Microscopy, Fluorescence, Mice, Knockout, Mice

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