The release of γ-aminobutyric acid (GABA) and ATP from rat β cells was monitored using an electrophysiological assay based on overexpression GABAA or P2X2 receptor ion channels. Exocytosis of LDCVs, detected by carbon fiber amperometry of serotonin, correlated strongly (∼80%) with ATP release. The increase in membrane capacitance per ATP release event was 3.4 fF, close to the expected capacitance of an individual LDCV with a diameter of 0.3 μm. ATP and GABA were coreleased with serotonin with the same probability. Immunogold electron microscopy revealed that ∼15% of the LDCVs contain GABA. Prespike “pedestals,” reflecting exit of granule constituents via the fusion pore, were less frequently observed for ATP than for serotonin or GABA and the relative amplitude (amplitude of foot compared to spike) was smaller: in some cases the ATP-dependent pedestal was missing entirely. An inward tonic current, not dependent on glucose and inhibited by the GABAA receptor antagonist SR95531, was observed in β cells in clusters of islet cells. Noise analysis indicated that it was due to the activity of individual channels with a conductance of 30 pS, the same as expected for individual GABAA Cl− channels with the ionic gradients used. We conclude that (a) LDCVs accumulate ATP and serotonin; (b) regulated release of GABA can be accounted for by exocytosis of a subset of insulin-containing LDCVs; (c) the fusion pore of LDCVs exhibits selectivity and compounds are differentially released depending on their chemical properties (including size); and (d) a glucose-independent nonvesicular form of GABA release exists in β cells.
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1 March 2007
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February 12 2007
Corelease and Differential Exit via the Fusion Pore of GABA, Serotonin, and ATP from LDCV in Rat Pancreatic β Cells
Matthias Braun,
Matthias Braun
1Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
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Anna Wendt,
Anna Wendt
2Department of Clinical Sciences, Clinical Research Centre, Lund University, 20502 Malmö, Sweden
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Jovita Karanauskaite,
Jovita Karanauskaite
1Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
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Juris Galvanovskis,
Juris Galvanovskis
1Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
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Anne Clark,
Anne Clark
1Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
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Patrick E. MacDonald,
Patrick E. MacDonald
1Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
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Patrik Rorsman
Patrik Rorsman
1Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
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Matthias Braun
1Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
Anna Wendt
2Department of Clinical Sciences, Clinical Research Centre, Lund University, 20502 Malmö, Sweden
Jovita Karanauskaite
1Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
Juris Galvanovskis
1Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
Anne Clark
1Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
Patrick E. MacDonald
1Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
Patrik Rorsman
1Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
Correspondence to Matthias Braun: [email protected]
M. Braun and A. Wendt contributed equally to this work.
P.E. MacDonald's present address is Department of Pharmacology, University of Alberta, Edmonton T6G 2E1, Canada.
Abbreviations used in this paper: GABA, γ-aminobutyric acid; LDCV, large dense-core vesicle; SLMV, synaptic-like microvesicle; TIC, transient inward current.
Received:
August 30 2006
Accepted:
January 26 2007
Online ISSN: 1540-7748
Print ISSN: 0022-1295
The Rockefeller University Press
2007
J Gen Physiol (2007) 129 (3): 221–231.
Article history
Received:
August 30 2006
Accepted:
January 26 2007
Citation
Matthias Braun, Anna Wendt, Jovita Karanauskaite, Juris Galvanovskis, Anne Clark, Patrick E. MacDonald, Patrik Rorsman; Corelease and Differential Exit via the Fusion Pore of GABA, Serotonin, and ATP from LDCV in Rat Pancreatic β Cells . J Gen Physiol 1 March 2007; 129 (3): 221–231. doi: https://doi.org/10.1085/jgp.200609658
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