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Multivesicular exocytosis in rat pancreatic beta cells

Hoppa, M. B.; Jones, E.; Karanauskaite, J.; Ramracheya, R.; Braun, M.; Collins, S. C.; Zhang, Q.; Clark, A.; Eliasson, Lena LU and Genoud, C., et al. (2012) In Diabetologia 55(4). p.1001-1012
Abstract
To establish the occurrence, modulation and functional significance of compound exocytosis in insulin-secreting beta cells. 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. 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... (More)
To establish the occurrence, modulation and functional significance of compound exocytosis in insulin-secreting beta cells. 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. 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 similar to 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 mu mol/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 mu m) 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. 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. (Less)
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Contribution to journal
publication status
published
subject
keywords
Exocytosis, Ca2+, Beta cell
in
Diabetologia
volume
55
issue
4
pages
1001 - 1012
publisher
Springer Verlag
external identifiers
  • wos:000301182000017
  • scopus:84862510135
ISSN
1432-0428
DOI
10.1007/s00125-011-2400-5
language
English
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yes
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9ccea088-6ed5-4123-ba06-2d512bc58fc1 (old id 2517010)
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2012-05-07 07:56:03
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2017-11-19 03:08:07
@article{9ccea088-6ed5-4123-ba06-2d512bc58fc1,
  abstract     = {To establish the occurrence, modulation and functional significance of compound exocytosis in insulin-secreting beta cells. 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. Compound exocytosis contributed marginally (&lt; 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 similar to 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 mu mol/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 mu m) 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. 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.},
  author       = {Hoppa, M. B. and Jones, E. and Karanauskaite, J. and Ramracheya, R. and Braun, M. and Collins, S. C. and Zhang, Q. and Clark, A. and Eliasson, Lena and Genoud, C. and MacDonald, P. E. and Monteith, A. G. and Barg, S. and Galvanovskis, J. and Rorsman, P.},
  issn         = {1432-0428},
  keyword      = {Exocytosis,Ca2+,Beta cell},
  language     = {eng},
  number       = {4},
  pages        = {1001--1012},
  publisher    = {Springer Verlag},
  series       = {Diabetologia},
  title        = {Multivesicular exocytosis in rat pancreatic beta cells},
  url          = {http://dx.doi.org/10.1007/s00125-011-2400-5},
  volume       = {55},
  year         = {2012},
}