Sequential exocytosis of insulin granules is associated with redistribution of SNAP25

Noriko Takahashi, Hiroyasu Hatakeyama, Haruo Okado, Akiko Miwa, Takuya Kishimoto, Tatsuya Kojima, Teruo Abe, Haruo Kasai

Research output: Contribution to journalArticlepeer-review

98 Citations (Scopus)


We have investigated sequential exocytosis in β cells of intact pancreatic islets with the use of two-photon excitation imaging of a polar fluorescent tracer, sulforhodamine B, and a fusion protein comprising enhanced cyan fluorescent protein (ECFP) and the SNARE protein SNAP25 (synaptosome-associated protein of 25 kD) transfected with an adenoviral vector. Sequential exocytosis was found to account for <10% of exocytic events in β cells stimulated either with glucose under various conditions or by photolysis of a caged-Ca2+ compound. Multigranular exocytosis, in which granule-to-granule fusion occurs before exocytosis, was rarely found. We detected redistribution of ECFP-SNAP25 from the plasma membrane into the membrane of the fused granule occurred in a large proportion (54%) of sequential exocytic events but in only a small fraction (5%) of solitary fusion events. Removal of cholesterol in the plasma membrane by methyl-β -cyclodextrin facilitated both redistribution of ECFP-SNAP25 and sequential exocytosis by threefold. These observations support the hypothesis that SNAP25 is a plasma membrane factor that is responsible for sequential exocytosis.

Original languageEnglish
Pages (from-to)255-262
Number of pages8
JournalJournal of Cell Biology
Issue number2
Publication statusPublished - 2004 Apr 26
Externally publishedYes


  • Diabetes
  • Pancreatic islet
  • Secretion
  • Two-photon imaging

ASJC Scopus subject areas

  • Cell Biology


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