IMR Press / FBL / Volume 16 / Issue 1 / DOI: 10.2741/3692

Frontiers in Bioscience-Landmark (FBL) is published by IMR Press from Volume 26 Issue 5 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on imrpress.com as a courtesy and upon agreement with Frontiers in Bioscience.

Open Access Article
Heterogeneous modes of insulin granule exocytosis: molecular determinants
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1 Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, 3-39-15 Showa-machi, Maebashi 371-8512, Japan
Academic Editor:Morten Pedersen
Front. Biosci. (Landmark Ed) 2011, 16(1), 360–367; https://doi.org/10.2741/3692
Published: 1 January 2011
(This article belongs to the Special Issue New aspects of biphasic insulin secretion)
Abstract

Glucose-induced insulin secretion is biphasic: the first phase forms a transient peak of secretion lasting a few minutes after the stimulation, whereas the second maintains a lower but persistent secretion rate. It was suggested that two different exocytic mechanisms operate during the two phases: the first phase exocytosis is derived from docked granules, whereas the second derives from newly recruited granules. However, total internal reflection fluorescence microscopy has revealed that, while the exocytosis in the first few minutes is derived from granules located close to the plasma membrane, it is also significantly effected by deeper granules, whereas that in the second phase is mainly derived from the deeper granules. Consistently, pancreatic beta cells deficient in the Rab27a effector, granuphilin, which is indispensable for the stable attachment (docking) of insulin granules to the plasma membrane, exhibit no delay or reduction of secretagogue-induced insulin secretion, and instead exhibit increased secretion. Future studies should explore the mechanism for time-dependent differences in the exocytic behaviors, namely the molecular determinants of the rate-limiting exocytic steps for docked and undocked granules.

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