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γ-Hydroxybutyrate does not mediate glucose inhibition of glucagon secretion
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Cell Biology.
Université Catholique de Louvain, Brussels, Belgium.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Cell Biology.
Karolinska Institutet.
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(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
National Category
Cell and Molecular Biology
Identifiers
URN: urn:nbn:se:uu:diva-356475OAI: oai:DiVA.org:uu-356475DiVA, id: diva2:1235883
Available from: 2018-07-29 Created: 2018-07-29 Last updated: 2018-07-31
In thesis
1. α-Cell signalling in glucose-regulated glucagon secretion
Open this publication in new window or tab >>α-Cell signalling in glucose-regulated glucagon secretion
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Glucagon is a blood glucose-elevating hormone released from α-cells in the islets of Langerhans during hypoglycaemia. Glucagon is critical for glucose homeostasis and inappropriate regulation of its secretion underlies both impaired counter-regulation of hypoglycaemia and chronic hyperglycaemia in diabetes patients. The mechanisms by which glucose controls glucagon secretion are poorly understood, but have been suggested to involve both direct effects of the sugar on α-cells and indirect effects mediated by paracrine factors released within the islet, including insulin and gamma-hydroxybutyrate (GHB) from β-cells, and somatostatin from δ-cells. This thesis addresses the role of the intracellular messengers ATP, Ca2+ and cAMP in glucose-regulated glucagon secretion. Various fluorescence microscopy techniques were used to monitor changes of these messengers in single, dispersed α-cells and those in situ within intact islets, and glucagon secretion from islets was measured with an immunoassay. Glucose induced elevations of α-cell ATP, which were smaller and showed a left-shifted concentration-dependence compared to those in β-cells, consistent with α-cells being less dependent on oxidative metabolism and optimized for sensing hypoglycaemia. α-Cells showed Ca2+ oscillations with little glucose dependence. Surprisingly, these oscillations became synchronized in phase with Ca2+ oscillations in β-cells at high glucose. Since Ca2+ is a main trigger of exocytosis in both cell types, and since insulin and glucagon secretion is pulsatile in opposite phase, the results indicate that factors other than Ca2+ are more important for shaping glucagon secretion. Consistent with a key role of cAMP for the regulation of glucagon release, the concentration of the messenger was relatively high in α-cells at low glucose concentrations, and elevations of glucose suppressed cAMP in parallel with glucagon secretion. This effect was independent of paracrine signalling from insulin and somatostatin. The glucose-induced suppression of glucagon secretion was prevented by cAMP-elevating agents and mimicked by inhibitors of protein kinase A. GHB lacked effects both on Ca2+, cAMP and glucagon secretion from mouse islets, but tended to stimulate glucagon secretion by a somatostatin-receptor-dependent mechanism in human islets. The data indicate that GHB is not an inhibitor of glucagon secretion and that α-cell-intrinsic glucose sensing involves signalling via cAMP and protein kinase A.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 49
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1478
Keywords
Islets, glucagon, insulin, somatostatin, ATP, cAMP, Ca2+, GHB, oscillations, α-cell, β-cell, δ-cell
National Category
Cell and Molecular Biology
Research subject
Medical Cell Biology
Identifiers
urn:nbn:se:uu:diva-356478 (URN)978-91-513-0387-1 (ISBN)
Public defence
2018-09-13, B21, Biomedical Centre, Husargatan 3, Uppsala, 09:15 (English)
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Supervisors
Available from: 2018-08-21 Created: 2018-07-31 Last updated: 2018-08-28

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