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Multivesicular exocytosis in rat pancreatic beta cells
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2012 (English)In: Diabetologia, ISSN 0012-186X, E-ISSN 1432-0428, Vol. 55, no 4, 1001-1012 p.Article in journal (Refereed) Published
Abstract [en]

AIMS/HYPOTHESIS

To establish the occurrence, modulation and functional significance of compound exocytosis in insulin-secreting beta cells.

METHODS

Exocytosis was monitored in rat beta cells by electrophysiological, biochemical and optical methods. The functional assays were complemented by three-dimensional reconstruction of confocal imaging, transmission and block face scanning electron microscopy to obtain ultrastructural evidence of compound exocytosis.

RESULTS

Compound exocytosis contributed marginally (<5% of events) to exocytosis elicited by glucose/membrane depolarisation alone. However, in beta cells stimulated by a combination of glucose and the muscarinic agonist carbachol, 15–20% of the release events were due to multivesicular exocytosis, but the frequency of exocytosis was not affected. The optical measurements suggest that carbachol should stimulate insulin secretion by ∼40%, similar to the observed enhancement of glucose-induced insulin secretion. The effects of carbachol were mimicked by elevating [Ca2+]i from 0.2 to 2 μmol/l Ca2+. Two-photon sulforhodamine imaging revealed exocytotic events about fivefold larger than single vesicles and that these structures, once formed, could persist for tens of seconds. Cells exposed to carbachol for 30 s contained long (1–2 μm) serpentine-like membrane structures adjacent to the plasma membrane. Three-dimensional electron microscopy confirmed the existence of fused multigranular aggregates within the beta cell, the frequency of which increased about fourfold in response to stimulation with carbachol.

CONCLUSIONS/INTERPRETATION

Although contributing marginally to glucose-induced insulin secretion, compound exocytosis becomes quantitatively significant under conditions associated with global elevation of cytoplasmic calcium. These findings suggest that compound exocytosis is a major contributor to the augmentation of glucose-induced insulin secretion by muscarinic receptor activation.

Place, publisher, year, edition, pages
2012. Vol. 55, no 4, 1001-1012 p.
Keyword [en]
Beta cell, Ca2+, exocytosis
National Category
Cell and Molecular Biology
Identifiers
URN: urn:nbn:se:uu:diva-166043DOI: 10.1007/s00125-011-2400-5ISI: 000301182000017PubMedID: 22189485OAI: oai:DiVA.org:uu-166043DiVA: diva2:475114
Available from: 2012-01-10 Created: 2012-01-10 Last updated: 2017-12-08Bibliographically approved

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Barg, Sebastian

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