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Armour SL, Frueh A, Chibalina MV, Dou H, Argemi-Muntadas L, Hamilton A, Katzilieris-Petras G, Carmeliet P, Davies B, Moritz T, Eliasson L, Rorsman P, Knudsen JG. Glucose Controls Glucagon Secretion by Regulating Fatty Acid Oxidation in Pancreatic α-Cells. Diabetes 2023; 72:1446-1459. [PMID: 37494670 PMCID: PMC10545563 DOI: 10.2337/db23-0056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Accepted: 07/16/2023] [Indexed: 07/28/2023]
Abstract
Whole-body glucose homeostasis is coordinated through secretion of glucagon and insulin from pancreatic islets. When glucose is low, glucagon is released from α-cells to stimulate hepatic glucose production. However, the mechanisms that regulate glucagon secretion from pancreatic α-cells remain unclear. Here we show that in α-cells, the interaction between fatty acid oxidation and glucose metabolism controls glucagon secretion. The glucose-dependent inhibition of glucagon secretion relies on pyruvate dehydrogenase and carnitine palmitoyl transferase 1a activity and lowering of mitochondrial fatty acid oxidation by increases in glucose. This results in reduced intracellular ATP and leads to membrane repolarization and inhibition of glucagon secretion. These findings provide a new framework for the metabolic regulation of the α-cell, where regulation of fatty acid oxidation by glucose accounts for the stimulation and inhibition of glucagon secretion. ARTICLE HIGHLIGHTS It has become clear that dysregulation of glucagon secretion and α-cell function plays an important role in the development of diabetes, but we do not know how glucagon secretion is regulated. Here we asked whether glucose inhibits fatty acid oxidation in α-cells to regulate glucagon secretion. We found that fatty acid oxidation is required for the inhibitory effects of glucose on glucagon secretion through reductions in ATP. These findings provide a new framework for the regulation of glucagon secretion by glucose.
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Affiliation(s)
- Sarah L. Armour
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Alexander Frueh
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Margarita V. Chibalina
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, U.K
| | - Haiqiang Dou
- Department of Physiology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Lidia Argemi-Muntadas
- Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Alexander Hamilton
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
- Department of Clinical Sciences in Malmö, Islet Cell Exocytosis, Lund University Diabetes Centre, Lund University, Malmö, Sweden
| | - Georgios Katzilieris-Petras
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Peter Carmeliet
- Laboratory of Angiogenesis and Vascular Metabolism, Centre for Cancer Biology, Vlaams Instituut voor Biotechnologie (VIB), Department of Oncology, Leuven Cancer Institute, Katholieke Universiteit Leuven, Leuven, Belgium
- Laboratory of Angiogenesis and Vascular Heterogeneity, Department of Biomedicine, Aarhus University, Aarhus, Denmark
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangdong, People’s Republic of China
| | - Benjamin Davies
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, U.K
| | - Thomas Moritz
- Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lena Eliasson
- Department of Clinical Sciences in Malmö, Islet Cell Exocytosis, Lund University Diabetes Centre, Lund University, Malmö, Sweden
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, U.K
- Department of Physiology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Jakob G. Knudsen
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
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2
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Abstract
Plasma glucose is tightly regulated via the secretion of the two glucose-regulating hormones insulin and glucagon. Situated next to the insulin-secreting β-cells, the α-cells produce and secrete glucagon-one of the body's few blood glucose-increasing hormones. Diabetes is a bihormonal disorder, resulting from both inadequate insulin secretion and dysregulation of glucagon. The year 2023 marks the 100th anniversary of the discovery of glucagon, making it particularly timely to highlight the roles of this systemic metabolic messenger in health and disease.
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Affiliation(s)
- Patrick E MacDonald
- Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
- Department of Pharmacology, University of Alberta, Edmonton, AB, Canada
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford, UK.
- Metabolic Physiology, Institute of Neuroscience and Physiology, University of Göteborg, Gothenburg, Sweden.
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3
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Miranda C, Begum M, Vergari E, Briant LJB. Gap junction coupling and islet delta-cell function in health and disease. Peptides 2022; 147:170704. [PMID: 34826505 DOI: 10.1016/j.peptides.2021.170704] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 11/12/2021] [Accepted: 11/19/2021] [Indexed: 12/12/2022]
Abstract
The pancreatic islets contain beta-cells and alpha-cells, which are responsible for secreting two principal gluco-regulatory hormones; insulin and glucagon, respectively. However, they also contain delta-cells, a relatively sparse cell type that secretes somatostatin (SST). These cells have a complex morphology allowing them to establish an extensive communication network throughout the islet, despite their scarcity. Delta-cells are electrically excitable cells, and SST secretion is released in a glucose- and KATP-dependent manner. SST hyperpolarises the alpha-cell membrane and suppresses exocytosis. In this way, islet SST potently inhibits glucagon release. Recent studies investigating the activity of delta-cells have revealed they are electrically coupled to beta-cells via gap junctions, suggesting the delta-cell is more than just a paracrine inhibitor. In this Review, we summarize delta-cell morphology, function, and the role of SST signalling for regulating islet hormonal output. A distinguishing feature of this Review is that we attempt to use the discovery of this gap junction pathway, together with what is already known about delta-cells, to reframe the role of these cells in both health and disease. In particular, we argue that the discovery of gap junction communication between delta-cells and beta-cells provides new insights into the contribution of delta-cells to the islet hormonal defects observed in both type 1 and type 2 diabetes. This reappraisal of the delta-cell is important as it may offer novel insights into how the physiology of this cell can be utilised to restore islet function in diabetes.
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Affiliation(s)
- Caroline Miranda
- Institute of Neuroscience and Physiology, Metabolic Research Unit, University of Göteborg, 405 30, Göteborg, Sweden
| | - Manisha Begum
- Institute of Neuroscience and Physiology, Metabolic Research Unit, University of Göteborg, 405 30, Göteborg, Sweden; University of Skӧvde, Department of Infection Biology, Högskolevägen 1, 541 28, Skövde, Sweden
| | - Elisa Vergari
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, OX4 7LE, Oxford, UK
| | - Linford J B Briant
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, OX4 7LE, Oxford, UK; Department of Computer Science, University of Oxford, OX1 3QD, Oxford, UK.
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4
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Dudek KD, Osipovich AB, Cartailler JP, Gu G, Magnuson MA. Insm1, Neurod1, and Pax6 promote murine pancreatic endocrine cell development through overlapping yet distinct RNA transcription and splicing programs. G3-GENES GENOMES GENETICS 2021; 11:6358139. [PMID: 34534285 PMCID: PMC8527475 DOI: 10.1093/g3journal/jkab303] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Accepted: 08/19/2021] [Indexed: 11/13/2022]
Abstract
Insm1, Neurod1, and Pax6 are essential for the formation and function of pancreatic endocrine cells. Here, we report comparative immunohistochemical, transcriptomic, functional enrichment, and RNA splicing analyses of these genes using gene knock-out mice. Quantitative immunohistochemical analysis confirmed that elimination of each of these three factors variably impairs the proliferation, survival, and differentiation of endocrine cells. Transcriptomic analysis revealed that each factor contributes uniquely to the transcriptome although their effects were overlapping. Functional enrichment analysis revealed that genes downregulated by the elimination of Insm1, Neurod1, and Pax6 are commonly involved in mRNA metabolism, chromatin organization, secretion, and cell cycle regulation, and upregulated genes are associated with protein degradation, autophagy, and apoptotic process. Elimination of Insm1, Neurod1, and Pax6 impaired expression of many RNA-binding proteins thereby altering RNA splicing events, including for Syt14 and Snap25, two genes required for insulin secretion. All three factors are necessary for normal splicing of Syt14, and both Insm1 and Pax6 are necessary for the processing of Snap25. Collectively, these data provide new insights into how Insm1, Neurod1, and Pax6 contribute to the formation of functional pancreatic endocrine cells.
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Affiliation(s)
- Karrie D Dudek
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37232, USA.,Center for Stem Cell Biology, Vanderbilt University, Nashville, TN 37232, USA
| | - Anna B Osipovich
- Center for Stem Cell Biology, Vanderbilt University, Nashville, TN 37232, USA.,Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
| | | | - Guoquing Gu
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37232, USA.,Center for Stem Cell Biology, Vanderbilt University, Nashville, TN 37232, USA
| | - Mark A Magnuson
- Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37232, USA.,Center for Stem Cell Biology, Vanderbilt University, Nashville, TN 37232, USA.,Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
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Acreman S, Zhang Q. Regulation of α-cell glucagon secretion: The role of second messengers. Chronic Dis Transl Med 2021; 8:7-18. [PMID: 35620162 PMCID: PMC9128566 DOI: 10.1016/j.cdtm.2021.06.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Accepted: 06/15/2021] [Indexed: 11/30/2022] Open
Abstract
Glucagon is a potent glucose‐elevating hormone that is secreted by pancreatic α‐cells. While well‐controlled glucagon secretion plays an important role in maintaining systemic glucose homeostasis and preventing hypoglycaemia, it is increasingly apparent that defects in the regulation of glucagon secretion contribute to impaired counter‐regulation and hyperglycaemia in diabetes. It has therefore been proposed that pharmacological interventions targeting glucagon secretion/signalling can have great potential in improving glycaemic control of patients with diabetes. However, despite decades of research, a consensus on the precise mechanisms of glucose regulation of glucagon secretion is yet to be reached. Second messengers are a group of small intracellular molecules that relay extracellular signals to the intracellular signalling cascade, modulating cellular functions. There is a growing body of evidence that second messengers, such as cAMP and Ca2+, play critical roles in α‐cell glucose‐sensing and glucagon secretion. In this review, we discuss the impact of second messengers on α‐cell electrical activity, intracellular Ca2+ dynamics and cell exocytosis. We highlight the possibility that the interaction between different second messengers may play a key role in the glucose‐regulation of glucagon secretion.
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Singh B, Khattab F, Chae H, Desmet L, Herrera PL, Gilon P. K ATP channel blockers control glucagon secretion by distinct mechanisms: A direct stimulation of α-cells involving a [Ca 2+] c rise and an indirect inhibition mediated by somatostatin. Mol Metab 2021; 53:101268. [PMID: 34118477 PMCID: PMC8274344 DOI: 10.1016/j.molmet.2021.101268] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Revised: 05/10/2021] [Accepted: 06/03/2021] [Indexed: 02/06/2023] Open
Abstract
Objective Glucagon is secreted by pancreatic α-cells in response to hypoglycemia and its hyperglycemic effect helps to restore normal blood glucose. Insulin and somatostatin (SST) secretions from β- and δ-cells, respectively, are stimulated by glucose by mechanisms involving an inhibition of their ATP-sensitive K+ (KATP) channels, leading to an increase in [Ca2+]c that triggers exocytosis. Drugs that close KATP channels, such as sulfonylureas, are used to stimulate insulin release in type 2 diabetic patients. α-cells also express KATP channels. However, the mechanisms by which sulfonylureas control glucagon secretion are still largely debated and were addressed in the present study. In particular, we studied the effects of KATP channel blockers on α-cell [Ca2+]c and glucagon secretion in the presence of a low (1 mM) or a high (15 mM) glucose concentration and evaluated the role of SST in these effects. Methods Using a transgenic mouse model expressing the Ca2+-sensitive fluorescent protein, GCaMP6f, specifically in α-cells, we measured [Ca2+]c in α-cells either dispersed or within whole islets (by confocal microscopy). By measuring [Ca2+]c in α-cells within islets and glucagon secretion using the same perifusion protocols, we tested whether glucagon secretion correlated with changes in [Ca2+]c in response to sulfonylureas. We studied the role of SST in the effects of sulfonylureas using multiple approaches including genetic ablation of SST, or application of SST-14 and SST receptor antagonists. Results Application of the sulfonylureas, tolbutamide, or gliclazide, to a medium containing 1 mM or 15 mM glucose increased [Ca2+]c in α-cells by a direct effect as in β-cells. At low glucose, sulfonylureas inhibited glucagon secretion of islets despite the rise in α-cell [Ca2+]c that they triggered. This glucagonostatic effect was indirect and attributed to SST because, in the islets of SST-knockout mice, sulfonylureas induced a stimulation of glucagon secretion which correlated with an increase in α-cell [Ca2+]c. Experiments with exogenous SST-14 and SST receptor antagonists indicated that the glucagonostatic effect of sulfonylureas mainly resulted from an inhibition of the efficacy of cytosolic Ca2+ on exocytosis. Although SST-14 was also able to inhibit glucagon secretion by decreasing α-cell [Ca2+]c, no decrease in [Ca2+]c occurred during sulfonylurea application because it was largely counterbalanced by the direct stimulatory effect of these drugs on α-cell [Ca2+]c. At high glucose, i.e., in conditions where glucagon release was already low, sulfonylureas stimulated glucagon secretion because their direct stimulatory effect on α-cells exceeded the indirect effect by SST. Our results also indicated that, unexpectedly, SST-14 poorly decreased the efficacy of Ca2+ on exocytosis in β-cells. Conclusions Sulfonylureas exert two opposite actions on α-cells: a direct stimulation as in β-cells and an indirect inhibition by SST. This suggests that any alteration of SST paracrine influence, as described in diabetes, will modify the effect of sulfonylureas on glucagon release. In addition, we suggest that δ-cells inhibit α-cells more efficiently than β-cells. KATP channel blockers control glucagon secretion by two mechanisms. The first one is the direct stimulation of α-cell by a [Ca2+]c rise, as in β-cells. The second one is an indirect inhibition mediated by δ-cells releasing somatostatin. Somatostatin mainly reduces the efficacy of Ca2+ on exocytosis in α-cells. Somatostatin more potently inhibits glucagon than insulin secretion.
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Affiliation(s)
- Bilal Singh
- Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle d'Endocrinologie, Diabète et Nutrition, Brussels, Belgium
| | - Firas Khattab
- Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle d'Endocrinologie, Diabète et Nutrition, Brussels, Belgium
| | - Heeyoung Chae
- Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle d'Endocrinologie, Diabète et Nutrition, Brussels, Belgium
| | - Lieven Desmet
- Université Catholique de Louvain, SMCS, Louvain Institute of Data Analysis and Modeling in economics and statistics, Louvain-la-Neuve, Belgium
| | - Pedro L Herrera
- Department of Genetic Medicine and Development, Faculty of Medicine, University of Geneva, Geneva, Switzerland
| | - Patrick Gilon
- Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle d'Endocrinologie, Diabète et Nutrition, Brussels, Belgium.
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7
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Gao R, Yang T, Zhang Q. δ-Cells: The Neighborhood Watch in the Islet Community. BIOLOGY 2021; 10:biology10020074. [PMID: 33494193 PMCID: PMC7909827 DOI: 10.3390/biology10020074] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Revised: 01/19/2021] [Accepted: 01/19/2021] [Indexed: 12/29/2022]
Abstract
Somatostatin-secreting δ-cells have aroused great attention due to their powerful roles in coordination of islet insulin and glucagon secretion and maintenance of glucose homeostasis. δ-cells exhibit neuron-like morphology with projections which enable pan-islet somatostatin paracrine regulation despite their scarcity in the islets. The expression of a range of hormone and neurotransmitter receptors allows δ-cells to integrate paracrine, endocrine, neural and nutritional inputs, and provide rapid and precise feedback modulations on glucagon and insulin secretion from α- and β-cells, respectively. Interestingly, the paracrine tone of δ-cells can be effectively modified in response to factors released by neighboring cells in this interactive communication, such as insulin, urocortin 3 and γ-aminobutyric acid from β-cells, glucagon, glutamate and glucagon-like peptide-1 from α-cells. In the setting of diabetes, defects in δ-cell function lead to suboptimal insulin and glucagon outputs and lift the glycemic set-point. The interaction of δ-cells and non-δ-cells also becomes defective in diabetes, with reduces paracrine feedback to β-cells to exacerbate hyperglycemia or enhanced inhibition of α-cells, disabling counter-regulation, to cause hypoglycemia. Thus, it is possible to restore/optimize islet function in diabetes targeting somatostatin signaling, which could open novel avenues for the development of effective diabetic treatments.
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Affiliation(s)
- Rui Gao
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK;
- Department of Endocrinology and Metabolism, The First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, China;
| | - Tao Yang
- Department of Endocrinology and Metabolism, The First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, China;
| | - Quan Zhang
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford OX3 7LE, UK;
- Correspondence:
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Zhang Q, Dou H, Rorsman P. 'Resistance is futile?' - paradoxical inhibitory effects of K ATP channel closure in glucagon-secreting α-cells. J Physiol 2020; 598:4765-4780. [PMID: 32716554 PMCID: PMC7689873 DOI: 10.1113/jp279775] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2020] [Accepted: 07/24/2020] [Indexed: 12/12/2022] Open
Abstract
By secreting insulin and glucagon, the β- and α-cells of the pancreatic islets play a central role in the regulation of systemic metabolism. Both cells are equipped with ATP-regulated potassium (KATP ) channels that are regulated by the intracellular ATP/ADP ratio. In β-cells, KATP channels are active at low (non-insulin-releasing) glucose concentrations. An increase in glucose leads to KATP channel closure, membrane depolarization and electrical activity that culminates in elevation of [Ca2+ ]i and initiation of exocytosis of the insulin-containing secretory granules. The α-cells are also equipped with KATP channels but they are under strong tonic inhibition at low glucose, explaining why α-cells are electrically active under hypoglycaemic conditions and generate large Na+ - and Ca2+ -dependent action potentials. Closure of residual KATP channel activity leads to membrane depolarization and an increase in action potential firing but this stimulation of electrical activity is associated with inhibition rather than acceleration of glucagon secretion. This paradox arises because membrane depolarization reduces the amplitude of the action potentials by voltage-dependent inactivation of the Na+ channels involved in action potential generation. Exocytosis in α-cells is tightly linked to the opening of voltage-gated P/Q-type Ca2+ channels, the activation of which is steeply voltage-dependent. Accordingly, the inhibitory effect of the reduced action potential amplitude exceeds the stimulatory effect resulting from the increased action potential frequency. These observations highlight a previously unrecognised role of the action potential amplitude as a key regulator of pancreatic islet hormone secretion.
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Affiliation(s)
- Quan Zhang
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Churchill Hospital, Oxford, OX3 7LE, UK
| | - Haiqiang Dou
- Metabolic Physiology Unit, Institute of Neuroscience and Physiology, University of Göteborg, PO Box 430, Göteborg, SE-405 30, Sweden
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Churchill Hospital, Oxford, OX3 7LE, UK.,Metabolic Physiology Unit, Institute of Neuroscience and Physiology, University of Göteborg, PO Box 430, Göteborg, SE-405 30, Sweden
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9
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Félix-Martínez GJ, González-Vélez V, Godínez-Fernández JR, Gil A. Electrophysiological models of the human pancreatic δ-cell: From single channels to the firing of action potentials. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2020; 36:e3296. [PMID: 31833669 DOI: 10.1002/cnm.3296] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Revised: 12/05/2019] [Accepted: 12/05/2019] [Indexed: 06/10/2023]
Abstract
Minimal mathematical models were developed to describe the electrophysiological properties of human δ-cells. Markov models of single channels were first developed based on the analysis of electrophysiological data. Monte Carlo simulations of voltage-clamp experiments were performed in an iteratively optimization procedure to estimate the number of channels required to reproduce the main characteristics of the macroscopic currents recorded experimentally. A membrane model of the firing of action potentials was then developed based on the kinetic schemes of single channels and the number of channels estimated. We showed that macroscopic currents of human δ-cells can be reproduced by minimal models of single channels when the appropriate number of channels is considered. In addition, our simulations suggest that human δ-cells are capable of generating action potentials through the interaction of the ionic currents involved. Finally, we determined the relative contribution of the currents underlying the firing of action potentials in human pancreatic δ-cells, which allowed us to propose a qualitative model of an action potential in terms of the underlying ionic currents.
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Affiliation(s)
- Gerardo J Félix-Martínez
- Cátedras CONACYT, Consejo Nacional de Ciencia y Tecnología, Mexico City, Mexico
- Departamento de Ingeniería Eléctrica, Universidad Autónoma Metropolitana, Mexico City, Mexico
| | | | | | - Amparo Gil
- Departamento de Matemática Aplicada y Ciencias de la Computación, Universidad de Cantabria, Santander, Spain
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Selvaraj C, Selvaraj G, Kaliamurthi S, Cho WC, Wei DQ, Singh SK. Ion Channels as Therapeutic Targets for Type 1 Diabetes Mellitus. Curr Drug Targets 2020; 21:132-147. [PMID: 31538892 DOI: 10.2174/1389450119666190920152249] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Revised: 08/06/2019] [Accepted: 08/07/2019] [Indexed: 02/07/2023]
Abstract
Ion channels are integral proteins expressed in almost all living cells and are involved in muscle contraction and nutrient transport. They play a critical role in the normal functioning of the excitable tissues of the nervous system and regulate the action potential and contraction events. Dysfunction of genes encodes ion channel proteins, which disrupt the channel function and lead to a number of diseases, among which is type 1 diabetes mellitus (T1DM). Therefore, understanding the complex mechanism of ion channel receptors is necessary to facilitate the diagnosis and management of treatment. In this review, we summarize the mechanism of important ion channels and their potential role in the regulation of insulin secretion along with the limitations of ion channels as therapeutic targets. Furthermore, we discuss the recent investigations of the mechanism regulating the ion channels in pancreatic beta cells, which suggest that ion channels are active participants in the regulation of insulin secretion.
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Affiliation(s)
- Chandrabose Selvaraj
- Department of Bioinformatics, Computer-Aided Drug Design, and Molecular Modeling Lab, Science Block, Alagappa University, Karaikudi, Tamil Nadu, 630004, India
| | - Gurudeeban Selvaraj
- Center of Interdisciplinary Sciences-Computational Life Sciences, College of Food Science and Engineering, Henan University of Technology, Zhengzhou, 450001, China
- Peng Cheng Laboratory, Vanke Cloud City Phase I Building 8, Xili Street, Nanshan District, Shenzhen, Guangdong, 518055, China
| | - Satyavani Kaliamurthi
- Center of Interdisciplinary Sciences-Computational Life Sciences, College of Food Science and Engineering, Henan University of Technology, Zhengzhou, 450001, China
- Peng Cheng Laboratory, Vanke Cloud City Phase I Building 8, Xili Street, Nanshan District, Shenzhen, Guangdong, 518055, China
| | - William C Cho
- Department of Clinical Oncology, Queen Elizabeth Hospital, Kowloon, Hong Kong
| | - Dong-Qing Wei
- Center of Interdisciplinary Sciences-Computational Life Sciences, College of Food Science and Engineering, Henan University of Technology, Zhengzhou, 450001, China
- Peng Cheng Laboratory, Vanke Cloud City Phase I Building 8, Xili Street, Nanshan District, Shenzhen, Guangdong, 518055, China
- Department of Bioinformatics, The State Key Laboratory of Microbial Metabolism, College of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Sanjeev Kumar Singh
- Department of Bioinformatics, Computer-Aided Drug Design, and Molecular Modeling Lab, Science Block, Alagappa University, Karaikudi, Tamil Nadu, 630004, India
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12
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Noguchi GM, Huising MO. Integrating the inputs that shape pancreatic islet hormone release. Nat Metab 2019; 1:1189-1201. [PMID: 32694675 PMCID: PMC7378277 DOI: 10.1038/s42255-019-0148-2] [Citation(s) in RCA: 68] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Accepted: 11/07/2019] [Indexed: 02/06/2023]
Abstract
The pancreatic islet is a complex mini organ composed of a variety of endocrine cells and their support cells, which together tightly control blood glucose homeostasis. Changes in glucose concentration are commonly regarded as the chief signal controlling insulin-secreting beta cells, glucagon-secreting alpha cells and somatostatin-secreting delta cells. However, each of these cell types is highly responsive to a multitude of endocrine, paracrine, nutritional and neural inputs, which collectively shape the final endocrine output of the islet. Here, we review the principal inputs for each islet-cell type and the physiological circumstances in which these signals arise, through the prism of the insights generated by the transcriptomes of each of the major endocrine-cell types. A comprehensive integration of the factors that influence blood glucose homeostasis is essential to successfully improve therapeutic strategies for better diabetes management.
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Affiliation(s)
- Glyn M Noguchi
- Department of Neurobiology, Physiology & Behavior, College of Biological Sciences, University of California, Davis, Davis, CA, USA
| | - Mark O Huising
- Department of Neurobiology, Physiology & Behavior, College of Biological Sciences, University of California, Davis, Davis, CA, USA.
- Department of Physiology & Membrane Biology, School of Medicine, University of California, Davis, Davis, CA, USA.
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13
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Denwood G, Tarasov A, Salehi A, Vergari E, Ramracheya R, Takahashi H, Nikolaev VO, Seino S, Gribble F, Reimann F, Rorsman P, Zhang Q. Glucose stimulates somatostatin secretion in pancreatic δ-cells by cAMP-dependent intracellular Ca 2+ release. J Gen Physiol 2019; 151:1094-1115. [PMID: 31358556 PMCID: PMC6719402 DOI: 10.1085/jgp.201912351] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2019] [Revised: 05/11/2019] [Accepted: 07/09/2019] [Indexed: 12/12/2022] Open
Abstract
Somatostatin secretion from pancreatic islet δ-cells is stimulated by elevated glucose levels, but the underlying mechanisms have only partially been elucidated. Here we show that glucose-induced somatostatin secretion (GISS) involves both membrane potential-dependent and -independent pathways. Although glucose-induced electrical activity triggers somatostatin release, the sugar also stimulates GISS via a cAMP-dependent stimulation of CICR and exocytosis of somatostatin. The latter effect is more quantitatively important and in mouse islets depolarized by 70 mM extracellular K+ , increasing glucose from 1 mM to 20 mM produced an ∼3.5-fold stimulation of somatostatin secretion, an effect that was mimicked by the application of the adenylyl cyclase activator forskolin. Inhibiting cAMP-dependent pathways with PKI or ESI-05, which inhibit PKA and exchange protein directly activated by cAMP 2 (Epac2), respectively, reduced glucose/forskolin-induced somatostatin secretion. Ryanodine produced a similar effect that was not additive to that of the PKA or Epac2 inhibitors. Intracellular application of cAMP produced a concentration-dependent stimulation of somatostatin exocytosis and elevation of cytoplasmic Ca2+ ([Ca2+]i). Both effects were inhibited by ESI-05 and thapsigargin (an inhibitor of SERCA). By contrast, inhibition of PKA suppressed δ-cell exocytosis without affecting [Ca2+]i Simultaneous recordings of electrical activity and [Ca2+]i in δ-cells expressing the genetically encoded Ca2+ indicator GCaMP3 revealed that the majority of glucose-induced [Ca2+]i spikes did not correlate with δ-cell electrical activity but instead reflected Ca2+ release from the ER. These spontaneous [Ca2+]i spikes are resistant to PKI but sensitive to ESI-05 or thapsigargin. We propose that cAMP links an increase in plasma glucose to stimulation of somatostatin secretion by promoting CICR, thus evoking exocytosis of somatostatin-containing secretory vesicles in the δ-cell.
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Affiliation(s)
- Geoffrey Denwood
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, UK
| | - Andrei Tarasov
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, UK
- School of Life and Medical Sciences, University of Hertfordshire, Hatfield, UK
| | - Albert Salehi
- Institute of Neuroscience and Physiology, Department of Physiology, Metabolic Research Unit, University of Goteborg, Göteborg, Sweden
| | - Elisa Vergari
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, UK
| | - Reshma Ramracheya
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, UK
| | - Harumi Takahashi
- Division of Molecular and Metabolic Medicine, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Viacheslav O Nikolaev
- Institute of Experimental Cardiovascular Research, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Susumo Seino
- Division of Molecular and Metabolic Medicine, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Fiona Gribble
- Institute of Metabolic Science, University of Cambridge, Addenbrook's Hospital, Cambridge, UK
| | - Frank Reimann
- Institute of Metabolic Science, University of Cambridge, Addenbrook's Hospital, Cambridge, UK
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, UK
- Institute of Neuroscience and Physiology, Department of Physiology, Metabolic Research Unit, University of Goteborg, Göteborg, Sweden
| | - Quan Zhang
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, UK
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14
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Tengholm A. Cyclic AMP links glucose stimulation to somatostatin secretion in δ-cells. J Gen Physiol 2019; 151:1062-1065. [PMID: 31413066 PMCID: PMC6719405 DOI: 10.1085/jgp.201912417] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Tengholm reflects on new work providing insight into the mechanisms of glucose-stimulated somatostatin secretion from δ-cells.
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Affiliation(s)
- Anders Tengholm
- Department of Medical Cell Biology, Biomedical Centre, Uppsala University
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15
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Huising MO, van der Meulen T, Huang JL, Pourhosseinzadeh MS, Noguchi GM. The Difference δ-Cells Make in Glucose Control. Physiology (Bethesda) 2019; 33:403-411. [PMID: 30303773 DOI: 10.1152/physiol.00029.2018] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The role of beta and α-cells to glucose control are established, but the physiological role of δ-cells is poorly understood. Delta-cells are ideally positioned within pancreatic islets to modulate insulin and glucagon secretion at their source. We review the evidence for a negative feedback loop between delta and β-cells that determines the blood glucose set point and suggest that local δ-cell-mediated feedback stabilizes glycemic control.
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Affiliation(s)
- Mark O Huising
- Department of Neurobiology, Physiology & Behavior, College of Biological Sciences, University of California , Davis, California.,Department of Physiology and Membrane Biology, School of Medicine, University of California , Davis, California
| | - Talitha van der Meulen
- Department of Neurobiology, Physiology & Behavior, College of Biological Sciences, University of California , Davis, California
| | - Jessica L Huang
- Department of Neurobiology, Physiology & Behavior, College of Biological Sciences, University of California , Davis, California
| | - Mohammad S Pourhosseinzadeh
- Department of Neurobiology, Physiology & Behavior, College of Biological Sciences, University of California , Davis, California
| | - Glyn M Noguchi
- Department of Neurobiology, Physiology & Behavior, College of Biological Sciences, University of California , Davis, California
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16
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Vergari E, Knudsen JG, Ramracheya R, Salehi A, Zhang Q, Adam J, Asterholm IW, Benrick A, Briant LJB, Chibalina MV, Gribble FM, Hamilton A, Hastoy B, Reimann F, Rorsman NJG, Spiliotis II, Tarasov A, Wu Y, Ashcroft FM, Rorsman P. Insulin inhibits glucagon release by SGLT2-induced stimulation of somatostatin secretion. Nat Commun 2019; 10:139. [PMID: 30635569 PMCID: PMC6329806 DOI: 10.1038/s41467-018-08193-8] [Citation(s) in RCA: 115] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Accepted: 12/18/2018] [Indexed: 02/08/2023] Open
Abstract
Hypoglycaemia (low plasma glucose) is a serious and potentially fatal complication of insulin-treated diabetes. In healthy individuals, hypoglycaemia triggers glucagon secretion, which restores normal plasma glucose levels by stimulation of hepatic glucose production. This counterregulatory mechanism is impaired in diabetes. Here we show in mice that therapeutic concentrations of insulin inhibit glucagon secretion by an indirect (paracrine) mechanism mediated by stimulation of intra-islet somatostatin release. Insulin’s capacity to inhibit glucagon secretion is lost following genetic ablation of insulin receptors in the somatostatin-secreting δ-cells, when insulin-induced somatostatin secretion is suppressed by dapagliflozin (an inhibitor of sodium-glucose co-tranporter-2; SGLT2) or when the action of secreted somatostatin is prevented by somatostatin receptor (SSTR) antagonists. Administration of these compounds in vivo antagonises insulin’s hypoglycaemic effect. We extend these data to isolated human islets. We propose that SSTR or SGLT2 antagonists should be considered as adjuncts to insulin in diabetes therapy. Impaired glucagon secretion in patients with diabetes causes hypoglycemia. Here the authors show that therapeutic concentrations of insulin inhibit alpha-cell glucagon secretion by stimulating delta-cell insulin receptor and the release of somatostatin. Blocking somatostatin secretion or action ameliorates this effect.
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Affiliation(s)
- Elisa Vergari
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK
| | - Jakob G Knudsen
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK
| | - Reshma Ramracheya
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK
| | - Albert Salehi
- Department of Physiology, Institute of Neuroscience and Physiology, University of Göteborg, Box 430, Göteborg, SE40530, Sweden
| | - Quan Zhang
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK
| | - Julie Adam
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK
| | - Ingrid Wernstedt Asterholm
- Department of Physiology, Institute of Neuroscience and Physiology, University of Göteborg, Box 430, Göteborg, SE40530, Sweden
| | - Anna Benrick
- Department of Physiology, Institute of Neuroscience and Physiology, University of Göteborg, Box 430, Göteborg, SE40530, Sweden
| | - Linford J B Briant
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK
| | - Margarita V Chibalina
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK
| | - Fiona M Gribble
- Cambridge Institute of Metabolic Science and MRC Metabolic Diseases Unit, University of Cambridge School of Clinical Medicine, Cambridge Biomedical Campus, Hills Road, Cambridge, CB2 0QQ, UK
| | - Alexander Hamilton
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK
| | - Benoit Hastoy
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK
| | - Frank Reimann
- Cambridge Institute of Metabolic Science and MRC Metabolic Diseases Unit, University of Cambridge School of Clinical Medicine, Cambridge Biomedical Campus, Hills Road, Cambridge, CB2 0QQ, UK
| | - Nils J G Rorsman
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK
| | - Ioannis I Spiliotis
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK.,Oxford National Institute for Health Research, Biomedical Research Centre, Churchill Hospital, Oxford, OX3 7LE, UK
| | - Andrei Tarasov
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK.,Oxford National Institute for Health Research, Biomedical Research Centre, Churchill Hospital, Oxford, OX3 7LE, UK
| | - Yanling Wu
- Department of Physiology, Institute of Neuroscience and Physiology, University of Göteborg, Box 430, Göteborg, SE40530, Sweden
| | - Frances M Ashcroft
- Department of Physiology, Institute of Neuroscience and Physiology, University of Göteborg, Box 430, Göteborg, SE40530, Sweden.,Department of Physiology, Anatomy and Genetics, Henry Wellcome Centre for Gene Function, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Patrik Rorsman
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, Oxford, OX3 7LE, UK. .,Department of Physiology, Institute of Neuroscience and Physiology, University of Göteborg, Box 430, Göteborg, SE40530, Sweden. .,Oxford National Institute for Health Research, Biomedical Research Centre, Churchill Hospital, Oxford, OX3 7LE, UK.
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17
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Abstract
The somatostatin-secreting δ-cells comprise ~5% of the cells of the pancreatic islets. The δ-cells have complex morphology and might interact with many more islet cells than suggested by their low numbers. δ-Cells contain ATP-sensitive potassium channels, which open at low levels of glucose but close when glucose is elevated. This closure initiates membrane depolarization and electrical activity and increased somatostatin secretion. Factors released by neighbouring α-cells or β-cells amplify the glucose-induced effects on somatostatin secretion from δ-cells, which act locally within the islets as paracrine or autocrine inhibitors of insulin, glucagon and somatostatin secretion. The effects of somatostatin are mediated by activation of somatostatin receptors coupled to the inhibitory G protein, which culminates in suppression of the electrical activity and exocytosis in α-cells and β-cells. Somatostatin secretion is perturbed in animal models of diabetes mellitus, which might explain the loss of appropriate hypoglycaemia-induced glucagon secretion, a defect that could be mitigated by somatostatin receptor 2 antagonists. Somatostatin antagonists or agents that suppress somatostatin secretion have been proposed as an adjunct to insulin therapy. In this Review, we summarize the cell physiology of somatostatin secretion, what might go wrong in diabetes mellitus and the therapeutic potential of agents targeting somatostatin secretion or action.
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Affiliation(s)
- Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, Churchill Hospital, University of Oxford, Oxford, UK.
- Department of Neuroscience and Physiology, University of Gothenburg, Gothenburg, Sweden.
| | - Mark O Huising
- Department of Neurobiology, Physiology and Behavior, College of Biological Sciences, University of California, Davis, Davis, CA, USA
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, Davis, CA, USA
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18
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Proks P, Kramer H, Haythorne E, Ashcroft FM. Binding of sulphonylureas to plasma proteins - A KATP channel perspective. PLoS One 2018; 13:e0197634. [PMID: 29772022 PMCID: PMC5957440 DOI: 10.1371/journal.pone.0197634] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 05/04/2018] [Indexed: 12/25/2022] Open
Abstract
Sulphonylurea drugs stimulate insulin secretion from pancreatic β-cells primarily by inhibiting ATP sensitive potassium (KATP) channels in the β-cell membrane. The effective sulphonylurea concentration at its site of action is significantly attenuated by binding to serum albumin, which makes it difficult to compare in vitro and in vivo data. We therefore measured the ability of gliclazide and glibenclamide to inhibit KATP channels and stimulate insulin secretion in the presence of serum albumin. We used this data, together with estimates of free drug concentrations from binding studies, to predict the extent of sulphonylurea inhibition of KATP channels at therapeutic concentrations in vivo. KATP currents from mouse pancreatic β-cells and Xenopus oocytes were measured using the patch-clamp technique. Gliclazide and glibenclamide binding to human plasma were determined in spiked plasma samples using an ultrafiltration-mass spectrometry approach. Bovine serum albumin (60g/l) produced a mild, non-significant reduction of gliclazide block of KATP currents in pancreatic β-cells and Xenopus oocytes. In contrast, glibenclamide inhibition of recombinant KATP channels was dramatically suppressed by albumin (predicted free drug concentration <0.1%). Insulin secretion was also reduced. Free concentrations of gliclazide and glibenclamide in the presence of human plasma measured in binding experiments were 15% and 0.05%, respectively. Our data suggest the free concentration of glibenclamide in plasma is too low to account for the drug’s therapeutic effect. In contrast, the free gliclazide concentration in plasma is high enough to close KATP channels and stimulate insulin secretion.
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Affiliation(s)
- Peter Proks
- Oxford Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Holger Kramer
- Oxford Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Elizabeth Haythorne
- Oxford Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Frances M. Ashcroft
- Oxford Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
- * E-mail:
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19
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Rong X, Wei F, Luo RQ, Yuan X, Kuang QQ, Yin DP, Huang SS, Jiang YM, Liu H. Discrimination of Single Living Rat Pancreatic α, β, δ, and Pancreatic Polypeptide (PP) Cells Using Raman Spectroscopy. APPLIED SPECTROSCOPY 2018; 72:706-714. [PMID: 29350550 DOI: 10.1177/0003702818757993] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Primary pancreatic α, β, δ, and pancreatic polypeptide (PP) cells are reliable cell models for diabetes research. However, the separation and purification of these cells in living conditions remains an obstacle for researchers. The interaction of visible light with cellular molecules can produce Raman scattering, which can be analyzed to obtain cellular intrinsic molecular fingerprints. It has been speculated that primary pancreatic α, β, δ, and PP cells can be identified and separated from each other according to their spectral differences. To test this hypothesis, Raman spectra detection was performed on rat islet cells. Single islet cells identified by Raman scattering under living conditions were verified using immunohistochemistry. Thus, Raman data were acquired from a pure line of islet cells as a training sample and then used to establish the discriminant function. Then, using the principal component analysis-linear discriminate analysis (PCA-LDA) method, the four types of islet cells could be identified and discriminated by Raman spectroscopy. This study provides a label-free and noninvasive method for discriminating islet cell types in a randomly distributed mixed islet cell population via their physical properties rather than by using antibodies or fluorescence labeling.
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Affiliation(s)
- Xi Rong
- 1 The Department of Geriatric Endocrinology, the First Affiliated Hospital of 74626 Guangxi Medical University, Nanning, China
| | - Fang Wei
- 1 The Department of Geriatric Endocrinology, the First Affiliated Hospital of 74626 Guangxi Medical University, Nanning, China
| | - Rui-Qiong Luo
- 1 The Department of Geriatric Endocrinology, the First Affiliated Hospital of 74626 Guangxi Medical University, Nanning, China
| | - Xue Yuan
- 1 The Department of Geriatric Endocrinology, the First Affiliated Hospital of 74626 Guangxi Medical University, Nanning, China
| | - Qi-Qi Kuang
- 2 74626 Guangxi Medical University, Nanning, China
| | | | - Shu-Shi Huang
- 3 245477 The Laboratory of Biophysics, Guangxi Academy of Sciences, Nanning, China
| | - Yue-Ming Jiang
- 4 74626 Department of Health Toxicology, School of Public Health, Guangxi Medical University, Nanning, China
| | - Hong Liu
- 1 The Department of Geriatric Endocrinology, the First Affiliated Hospital of 74626 Guangxi Medical University, Nanning, China
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20
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Rorsman P, Ashcroft FM. Pancreatic β-Cell Electrical Activity and Insulin Secretion: Of Mice and Men. Physiol Rev 2018; 98:117-214. [PMID: 29212789 PMCID: PMC5866358 DOI: 10.1152/physrev.00008.2017] [Citation(s) in RCA: 456] [Impact Index Per Article: 76.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Revised: 05/30/2017] [Accepted: 06/18/2017] [Indexed: 12/14/2022] Open
Abstract
The pancreatic β-cell plays a key role in glucose homeostasis by secreting insulin, the only hormone capable of lowering the blood glucose concentration. Impaired insulin secretion results in the chronic hyperglycemia that characterizes type 2 diabetes (T2DM), which currently afflicts >450 million people worldwide. The healthy β-cell acts as a glucose sensor matching its output to the circulating glucose concentration. It does so via metabolically induced changes in electrical activity, which culminate in an increase in the cytoplasmic Ca2+ concentration and initiation of Ca2+-dependent exocytosis of insulin-containing secretory granules. Here, we review recent advances in our understanding of the β-cell transcriptome, electrical activity, and insulin exocytosis. We highlight salient differences between mouse and human β-cells, provide models of how the different ion channels contribute to their electrical activity and insulin secretion, and conclude by discussing how these processes become perturbed in T2DM.
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Affiliation(s)
- Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, United Kingdom; Department of Neuroscience and Physiology, Metabolic Research Unit, Göteborg, Sweden; and Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Frances M Ashcroft
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, United Kingdom; Department of Neuroscience and Physiology, Metabolic Research Unit, Göteborg, Sweden; and Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
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21
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Briant LJB, Reinbothe TM, Spiliotis I, Miranda C, Rodriguez B, Rorsman P. δ-cells and β-cells are electrically coupled and regulate α-cell activity via somatostatin. J Physiol 2017; 596:197-215. [PMID: 28975620 PMCID: PMC5767697 DOI: 10.1113/jp274581] [Citation(s) in RCA: 104] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Accepted: 09/25/2017] [Indexed: 12/28/2022] Open
Abstract
Key points We used a mouse expressing a light‐sensitive ion channel in β‐cells to understand how α‐cell activity is regulated by β‐cells. Light activation of β‐cells triggered a suppression of α‐cell activity via gap junction‐dependent activation of δ‐cells. Mathematical modelling of human islets suggests that 23% of the inhibitory effect of glucose on glucagon secretion is mediated by β‐cells via gap junction‐dependent activation of δ‐cells/somatostatin secretion.
Abstract Glucagon, the body's principal hyperglycaemic hormone, is released from α‐cells of the pancreatic islet. Secretion of this hormone is dysregulated in type 2 diabetes mellitus but the mechanisms controlling secretion are not well understood. Regulation of glucagon secretion by factors secreted by neighbouring β‐ and δ‐cells (paracrine regulation) have been proposed to be important. In this study, we explored the importance of paracrine regulation by using an optogenetic strategy. Specific light‐induced activation of β‐cells in mouse islets expressing the light‐gated channelrhodopsin‐2 resulted in stimulation of electrical activity in δ‐cells but suppression of α‐cell activity. Activation of the δ‐cells was rapid and sensitive to the gap junction inhibitor carbenoxolone, whereas the effect on electrical activity in α‐cells was blocked by CYN 154806, an antagonist of the somatostatin‐2 receptor. These observations indicate that optogenetic activation of the β‐cells propagates to the δ‐cells via gap junctions, and the consequential stimulation of somatostatin secretion inhibits α‐cell electrical activity by a paracrine mechanism. To explore whether this pathway is important for regulating α‐cell activity and glucagon secretion in human islets, we constructed computational models of human islets. These models had detailed architectures based on human islets and consisted of a collection of >500 α‐, β‐ and δ‐cells. Simulations of these models revealed that this gap junctional/paracrine mechanism accounts for up to 23% of the suppression of glucagon secretion by high glucose. We used a mouse expressing a light‐sensitive ion channel in β‐cells to understand how α‐cell activity is regulated by β‐cells. Light activation of β‐cells triggered a suppression of α‐cell activity via gap junction‐dependent activation of δ‐cells. Mathematical modelling of human islets suggests that 23% of the inhibitory effect of glucose on glucagon secretion is mediated by β‐cells via gap junction‐dependent activation of δ‐cells/somatostatin secretion.
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Affiliation(s)
- L J B Briant
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 7LE, UK.,Department of Computer Science, University of Oxford, Oxford, OX1 3QD, UK
| | - T M Reinbothe
- Metabolic Physiology, Department of Physiology, Institute of Neuroscience and Physiology, University of Gothenburg, SE-405 30, Gothenburg, Sweden
| | - I Spiliotis
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 7LE, UK
| | - C Miranda
- Metabolic Physiology, Department of Physiology, Institute of Neuroscience and Physiology, University of Gothenburg, SE-405 30, Gothenburg, Sweden
| | - B Rodriguez
- Department of Computer Science, University of Oxford, Oxford, OX1 3QD, UK
| | - P Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Radcliffe Department of Medicine, University of Oxford, Oxford, OX3 7LE, UK.,Metabolic Physiology, Department of Physiology, Institute of Neuroscience and Physiology, University of Gothenburg, SE-405 30, Gothenburg, Sweden
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22
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Kaczmarek LK, Zhang Y. Kv3 Channels: Enablers of Rapid Firing, Neurotransmitter Release, and Neuronal Endurance. Physiol Rev 2017; 97:1431-1468. [PMID: 28904001 PMCID: PMC6151494 DOI: 10.1152/physrev.00002.2017] [Citation(s) in RCA: 107] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 04/24/2017] [Accepted: 05/05/2017] [Indexed: 12/11/2022] Open
Abstract
The intrinsic electrical characteristics of different types of neurons are shaped by the K+ channels they express. From among the more than 70 different K+ channel genes expressed in neurons, Kv3 family voltage-dependent K+ channels are uniquely associated with the ability of certain neurons to fire action potentials and to release neurotransmitter at high rates of up to 1,000 Hz. In general, the four Kv3 channels Kv3.1-Kv3.4 share the property of activating and deactivating rapidly at potentials more positive than other channels. Each Kv3 channel gene can generate multiple protein isoforms, which contribute to the high-frequency firing of neurons such as auditory brain stem neurons, fast-spiking GABAergic interneurons, and Purkinje cells of the cerebellum, and to regulation of neurotransmitter release at the terminals of many neurons. The different Kv3 channels have unique expression patterns and biophysical properties and are regulated in different ways by protein kinases. In this review, we cover the function, localization, and modulation of Kv3 channels and describe how levels and properties of the channels are altered by changes in ongoing neuronal activity. We also cover how the protein-protein interaction of these channels with other proteins affects neuronal functions, and how mutations or abnormal regulation of Kv3 channels are associated with neurological disorders such as ataxias, epilepsies, schizophrenia, and Alzheimer's disease.
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Affiliation(s)
- Leonard K Kaczmarek
- Departments of Pharmacology and of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
| | - Yalan Zhang
- Departments of Pharmacology and of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
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23
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Li Y, Li F, Bai B, Wu Z, Hou X, Shen Y, Wang Y. Protein interacting with C‑kinase 1 modulates exocytosis and KATP conductance in pancreatic β cells. Mol Med Rep 2017; 16:4247-4252. [PMID: 28731156 DOI: 10.3892/mmr.2017.7056] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Accepted: 04/06/2017] [Indexed: 11/06/2022] Open
Abstract
It has been previously identified that α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptors (AMPARs) are expressed in pancreatic β cells and regulate exocytosis and insulin release. It is known that protein interacting with C‑kinase 1 (PICK1) regulates trafficking and synaptic targeting of AMPARs in the central nervous system. However, it is unknown whether PICK1 regulates glutamate‑induced insulin release in β cells. The present study demonstrated that glutamate‑induced exocytosis was increased in β cells derived from PICK1‑knockout mice. In agreement with this result, adding PICK1 in β cells reduced glutamate‑induced exocytosis, whereas adding EVKI, a peptide that interrupts the interaction between AMPARs and PICK1, increased the exocytosis of β cells with the application of glutamate. Furthermore, the conductance of ATP‑sensitive potassium (KATP) channels was reduced in PICK1‑knockout mice, which was reversed by the overexpression of PICK1. In addition, PICK1 application reduced voltage oscillation induced by the closure of KATP. Taken together, the results indicate that PICK1 regulates glutamate‑induced exocytosis in β cells.
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Affiliation(s)
- Yunhong Li
- Key Laboratory of Craniocerebral Diseases of Ningxia Hui Autonomous Region, Basic Medical College of Ningxia Medical University, Yinchuan, Ningxia 750004, P.R. China
| | - Fan Li
- Key Laboratory of Craniocerebral Diseases of Ningxia Hui Autonomous Region, Basic Medical College of Ningxia Medical University, Yinchuan, Ningxia 750004, P.R. China
| | - Bin Bai
- Department of Endocrinology, General Hospital of Ningxia Medical University, Yinchuan, Ningxia 750004, P.R. China
| | - Zhenyong Wu
- Department of Neurobiology, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, P.R. China
| | - Xiaolin Hou
- Department of Endocrinology, General Hospital of Ningxia Medical University, Yinchuan, Ningxia 750004, P.R. China
| | - Ying Shen
- Department of Neurobiology, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, P.R. China
| | - Yin Wang
- Key Laboratory of Craniocerebral Diseases of Ningxia Hui Autonomous Region, Basic Medical College of Ningxia Medical University, Yinchuan, Ningxia 750004, P.R. China
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24
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Müller TD, Finan B, Clemmensen C, DiMarchi RD, Tschöp MH. The New Biology and Pharmacology of Glucagon. Physiol Rev 2017; 97:721-766. [PMID: 28275047 DOI: 10.1152/physrev.00025.2016] [Citation(s) in RCA: 206] [Impact Index Per Article: 29.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
In the last two decades we have witnessed sizable progress in defining the role of gastrointestinal signals in the control of glucose and energy homeostasis. Specifically, the molecular basis of the huge metabolic benefits in bariatric surgery is emerging while novel incretin-based medicines based on endogenous hormones such as glucagon-like peptide 1 and pancreas-derived amylin are improving diabetes management. These and related developments have fostered the discovery of novel insights into endocrine control of systemic metabolism, and in particular a deeper understanding of the importance of communication across vital organs, and specifically the gut-brain-pancreas-liver network. Paradoxically, the pancreatic peptide glucagon has reemerged in this period among a plethora of newly identified metabolic macromolecules, and new data complement and challenge its historical position as a gut hormone involved in metabolic control. The synthesis of glucagon analogs that are biophysically stable and soluble in aqueous solutions has promoted biological study that has enriched our understanding of glucagon biology and ironically recruited glucagon agonism as a central element to lower body weight in the treatment of metabolic disease. This review summarizes the extensive historical record and the more recent provocative direction that integrates the prominent role of glucagon in glucose elevation with its under-acknowledged effects on lipids, body weight, and vascular health that have implications for the pathophysiology of metabolic diseases, and the emergence of precision medicines to treat metabolic diseases.
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Affiliation(s)
- T D Müller
- Institute for Diabetes and Obesity, Helmholtz Diabetes Center, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany; German Center for Diabetes Research, Neuherberg, Germany; Department of Chemistry, Indiana University, Bloomington, Indiana; Division of Metabolic Diseases, Technische Universität München, Munich, Germany
| | - B Finan
- Institute for Diabetes and Obesity, Helmholtz Diabetes Center, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany; German Center for Diabetes Research, Neuherberg, Germany; Department of Chemistry, Indiana University, Bloomington, Indiana; Division of Metabolic Diseases, Technische Universität München, Munich, Germany
| | - C Clemmensen
- Institute for Diabetes and Obesity, Helmholtz Diabetes Center, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany; German Center for Diabetes Research, Neuherberg, Germany; Department of Chemistry, Indiana University, Bloomington, Indiana; Division of Metabolic Diseases, Technische Universität München, Munich, Germany
| | - R D DiMarchi
- Institute for Diabetes and Obesity, Helmholtz Diabetes Center, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany; German Center for Diabetes Research, Neuherberg, Germany; Department of Chemistry, Indiana University, Bloomington, Indiana; Division of Metabolic Diseases, Technische Universität München, Munich, Germany
| | - M H Tschöp
- Institute for Diabetes and Obesity, Helmholtz Diabetes Center, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany; German Center for Diabetes Research, Neuherberg, Germany; Department of Chemistry, Indiana University, Bloomington, Indiana; Division of Metabolic Diseases, Technische Universität München, Munich, Germany
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25
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Briant LJB, Zhang Q, Vergari E, Kellard JA, Rodriguez B, Ashcroft FM, Rorsman P. Functional identification of islet cell types by electrophysiological fingerprinting. J R Soc Interface 2017; 14:20160999. [PMID: 28275121 PMCID: PMC5378133 DOI: 10.1098/rsif.2016.0999] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Accepted: 02/15/2017] [Indexed: 01/18/2023] Open
Abstract
The α-, β- and δ-cells of the pancreatic islet exhibit different electrophysiological features. We used a large dataset of whole-cell patch-clamp recordings from cells in intact mouse islets (N = 288 recordings) to investigate whether it is possible to reliably identify cell type (α, β or δ) based on their electrophysiological characteristics. We quantified 15 electrophysiological variables in each recorded cell. Individually, none of the variables could reliably distinguish the cell types. We therefore constructed a logistic regression model that included all quantified variables, to determine whether they could together identify cell type. The model identified cell type with 94% accuracy. This model was applied to a dataset of cells recorded from hyperglycaemic βV59M mice; it correctly identified cell type in all cells and was able to distinguish cells that co-expressed insulin and glucagon. Based on this revised functional identification, we were able to improve conductance-based models of the electrical activity in α-cells and generate a model of δ-cell electrical activity. These new models could faithfully emulate α- and δ-cell electrical activity recorded experimentally.
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Affiliation(s)
- Linford J B Briant
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, Radcliffe Department of Medicine, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK
- Department of Computer Science, University of Oxford, Oxford OX1 3QD, UK
| | - Quan Zhang
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, Radcliffe Department of Medicine, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK
| | - Elisa Vergari
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, Radcliffe Department of Medicine, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK
| | - Joely A Kellard
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, Radcliffe Department of Medicine, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK
| | - Blanca Rodriguez
- Department of Computer Science, University of Oxford, Oxford OX1 3QD, UK
| | - Frances M Ashcroft
- Department of Physiology, Anatomy, and Genetics, University of Oxford, South Parks Road, Oxford OX1 3PT, UK
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, Radcliffe Department of Medicine, University of Oxford, Churchill Hospital, Oxford OX3 7LE, UK
- Metabolic Research, Department of Physiology, Institute of Neuroscience and Physiology, University of Göteborg, SE-405 30 Göteborg, Sweden
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26
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Shuai H, Xu Y, Yu Q, Gylfe E, Tengholm A. Fluorescent protein vectors for pancreatic islet cell identification in live-cell imaging. Pflugers Arch 2016; 468:1765-77. [PMID: 27539300 PMCID: PMC5026721 DOI: 10.1007/s00424-016-1864-z] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2016] [Revised: 08/02/2016] [Accepted: 08/04/2016] [Indexed: 11/25/2022]
Abstract
The islets of Langerhans contain different types of endocrine cells, which are crucial for glucose homeostasis. β- and α-cells that release insulin and glucagon, respectively, are most abundant, whereas somatostatin-producing δ-cells and particularly pancreatic polypeptide-releasing PP-cells are more scarce. Studies of islet cell function are hampered by difficulties to identify the different cell types, especially in live-cell imaging experiments when immunostaining is unsuitable. The aim of the present study was to create a set of vectors for fluorescent protein expression with cell-type-specific promoters and evaluate their applicability in functional islet imaging. We constructed six adenoviral vectors for expression of red and green fluorescent proteins controlled by the insulin, preproglucagon, somatostatin, or pancreatic polypeptide promoters. After transduction of mouse and human islets or dispersed islet cells, a majority of the fluorescent cells also immunostained for the appropriate hormone. Recordings of the sub-plasma membrane Ca(2+) and cAMP concentrations with a fluorescent indicator and a protein biosensor, respectively, showed that labeled cells respond to glucose and other modulators of secretion and revealed a striking variability in Ca(2+) signaling among α-cells. The measurements allowed comparison of the phase relationship of Ca(2+) oscillations between different types of cells within intact islets. We conclude that the fluorescent protein vectors allow easy identification of specific islet cell types and can be used in live-cell imaging together with organic dyes and genetically encoded biosensors. This approach will facilitate studies of normal islet physiology and help to clarify molecular defects and disturbed cell interactions in diabetic islets.
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Affiliation(s)
- Hongyan Shuai
- Department of Medical Cell Biology, Uppsala University, Biomedical Centre, Box 571, SE-751 23, Uppsala, Sweden
| | - Yunjian Xu
- Department of Medical Cell Biology, Uppsala University, Biomedical Centre, Box 571, SE-751 23, Uppsala, Sweden
| | - Qian Yu
- Department of Medical Cell Biology, Uppsala University, Biomedical Centre, Box 571, SE-751 23, Uppsala, Sweden
| | - Erik Gylfe
- Department of Medical Cell Biology, Uppsala University, Biomedical Centre, Box 571, SE-751 23, Uppsala, Sweden
| | - Anders Tengholm
- Department of Medical Cell Biology, Uppsala University, Biomedical Centre, Box 571, SE-751 23, Uppsala, Sweden.
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27
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Watts M, Ha J, Kimchi O, Sherman A. Paracrine regulation of glucagon secretion: the β/α/δ model. Am J Physiol Endocrinol Metab 2016; 310:E597-E611. [PMID: 26837808 PMCID: PMC4835945 DOI: 10.1152/ajpendo.00415.2015] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 01/19/2016] [Indexed: 01/17/2023]
Abstract
The regulation of glucagon secretion in the pancreatic α-cell is not well understood. It has been proposed that glucose suppresses glucagon secretion either directly through an intrinsic mechanism within the α-cell or indirectly through an extrinsic mechanism. Previously, we described a mathematical model for isolated pancreatic α-cells and used it to investigate possible intrinsic mechanisms of regulating glucagon secretion. We demonstrated that glucose can suppress glucagon secretion through both ATP-dependent potassium channels (KATP) and a store-operated current (SOC). We have now developed an islet model that combines previously published mathematical models of α- and β-cells with a new model of δ-cells and use it to explore the effects of insulin and somatostatin on glucagon secretion. We show that the model can reproduce experimental observations that the inhibitory effect of glucose remains even when paracrine modulators are no longer acting on the α-cell. We demonstrate how paracrine interactions can either synchronize α- and δ-cells to produce pulsatile oscillations in glucagon and somatostatin secretion or fail to do so. The model can also account for the paradoxical observation that glucagon can be out of phase with insulin, whereas α-cell calcium is in phase with insulin. We conclude that both paracrine interactions and the α-cell's intrinsic mechanisms are needed to explain the response of glucagon secretion to glucose.
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Affiliation(s)
- Margaret Watts
- Laboratory of Biological Modeling, National Institutes of Health, Bethesda, Maryland; and
| | - Joon Ha
- Laboratory of Biological Modeling, National Institutes of Health, Bethesda, Maryland; and
| | - Ofer Kimchi
- Department of Physics, Princeton University, Princeton, New Jersey
| | - Arthur Sherman
- Laboratory of Biological Modeling, National Institutes of Health, Bethesda, Maryland; and
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28
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Inhibition of the malate-aspartate shuttle in mouse pancreatic islets abolishes glucagon secretion without affecting insulin secretion. Biochem J 2015; 468:49-63. [PMID: 25731850 DOI: 10.1042/bj20140697] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Altered secretion of insulin as well as glucagon has been implicated in the pathogenesis of Type 2 diabetes (T2D), but the mechanisms controlling glucagon secretion from α-cells largely remain unresolved. Therefore, we studied the regulation of glucagon secretion from αTC1-6 (αTC1 clone 6) cells and compared it with insulin release from INS-1 832/13 cells. We found that INS-1 832/13 and αTC1-6 cells respectively secreted insulin and glucagon concentration-dependently in response to glucose. In contrast, tight coupling of glycolytic and mitochondrial metabolism was observed only in INS-1 832/13 cells. Although glycolytic metabolism was similar in the two cell lines, TCA (tricarboxylic acid) cycle metabolism, respiration and ATP levels were less glucose-responsive in αTC1-6 cells. Inhibition of the malate-aspartate shuttle, using phenyl succinate (PhS), abolished glucose-provoked ATP production and hormone secretion from αTC1-6 but not INS-1 832/13 cells. Blocking the malate-aspartate shuttle increased levels of glycerol 3-phosphate only in INS-1 832/13 cells. Accordingly, relative expression of constituents in the glycerol phosphate shuttle compared with malate-aspartate shuttle was lower in αTC1-6 cells. Our data suggest that the glycerol phosphate shuttle augments the malate-aspartate shuttle in INS-1 832/13 but not αTC1-6 cells. These results were confirmed in mouse islets, where PhS abrogated secretion of glucagon but not insulin. Furthermore, expression of the rate-limiting enzyme of the glycerol phosphate shuttle was higher in sorted primary β- than in α-cells. Thus, suppressed glycerol phosphate shuttle activity in the α-cell may prevent a high rate of glycolysis and consequently glucagon secretion in response to glucose. Accordingly, pyruvate- and lactate-elicited glucagon secretion remains unaffected since their signalling is independent of mitochondrial shuttles.
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29
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Urocortin3 mediates somatostatin-dependent negative feedback control of insulin secretion. Nat Med 2015; 21:769-76. [PMID: 26076035 PMCID: PMC4496282 DOI: 10.1038/nm.3872] [Citation(s) in RCA: 180] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Accepted: 04/30/2015] [Indexed: 12/15/2022]
Abstract
The peptide hormone urocortin3 (Ucn3) is abundantly expressed by mature beta cells, yet its physiological role is unknown. Here we demonstrate that Ucn3 is stored and co-released with insulin and potentiates glucose-stimulated somatostatin secretion via cognate receptors on delta cells. Further, we found that islets lacking endogenous Ucn3 have fewer delta cells, reduced somatostatin content, impaired somatostatin secretion, and exaggerated insulin release, and that these defects are rectified by treatment with synthetic Ucn3 in vitro. Our observations indicate that the paracrine actions of Ucn3 activate a negative feedback loop that promotes somatostatin release to ensure the timely reduction of insulin secretion upon normalization of plasma glucose. Moreover, Ucn3 is markedly depleted from beta cells in mouse and macaque models of diabetes and in human diabetic islets. This suggests that Ucn3 is a key contributor to stable glycemic control, whose reduction during diabetes aggravates glycemic volatility and contributes to the pathophysiology of this disease.
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30
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Irles E, Ñeco P, Lluesma M, Villar-Pazos S, Santos-Silva JC, Vettorazzi JF, Alonso-Magdalena P, Carneiro EM, Boschero AC, Nadal Á, Quesada I. Enhanced glucose-induced intracellular signaling promotes insulin hypersecretion: pancreatic beta-cell functional adaptations in a model of genetic obesity and prediabetes. Mol Cell Endocrinol 2015; 404:46-55. [PMID: 25633666 DOI: 10.1016/j.mce.2015.01.033] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2014] [Revised: 01/20/2015] [Accepted: 01/21/2015] [Indexed: 12/13/2022]
Abstract
Obesity is associated with insulin resistance and is known to be a risk factor for type-2 diabetes. In obese individuals, pancreatic beta-cells try to compensate for the increased insulin demand in order to maintain euglycemia. Most studies have reported that this adaptation is due to morphological changes. However, the involvement of beta-cell functional adaptations in this process needs to be clarified. For this purpose, we evaluated different key steps in the glucose-stimulated insulin secretion (GSIS) in intact islets from female ob/ob obese mice and lean controls. Obese mice showed increased body weight, insulin resistance, hyperinsulinemia, glucose intolerance and fed hyperglycemia. Islets from ob/ob mice exhibited increased glucose-induced mitochondrial activity, reflected by enhanced NAD(P)H production and mitochondrial membrane potential hyperpolarization. Perforated patch-clamp examination of beta-cells within intact islets revealed several alterations in the electrical activity such as increased firing frequency and higher sensitivity to low glucose concentrations. A higher intracellular Ca(2+) mobilization in response to glucose was also found in ob/ob islets. Additionally, they displayed a change in the oscillatory pattern and Ca(2+) signals at low glucose levels. Capacitance experiments in intact islets revealed increased exocytosis in individual ob/ob beta-cells. All these up-regulated processes led to increased GSIS. In contrast, we found a lack of beta-cell Ca(2+) signal coupling, which could be a manifestation of early defects that lead to beta-cell malfunction in the progression to diabetes. These findings indicate that beta-cell functional adaptations are an important process in the compensatory response to obesity.
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Affiliation(s)
- Esperanza Irles
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Patricia Ñeco
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Mónica Lluesma
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Sabrina Villar-Pazos
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Junia Carolina Santos-Silva
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; Department of Structural and Functional Biology, Institute of Biology, State University of Campinas (UNICAMP), Campinas, Brazil
| | - Jean F Vettorazzi
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; Department of Structural and Functional Biology, Institute of Biology, State University of Campinas (UNICAMP), Campinas, Brazil
| | - Paloma Alonso-Magdalena
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Everardo M Carneiro
- Department of Structural and Functional Biology, Institute of Biology, State University of Campinas (UNICAMP), Campinas, Brazil
| | - Antonio C Boschero
- Department of Structural and Functional Biology, Institute of Biology, State University of Campinas (UNICAMP), Campinas, Brazil
| | - Ángel Nadal
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain
| | - Ivan Quesada
- Instituto de Bioingeniería, Universidad Miguel Hernández, Elche, Spain; CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Spain.
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31
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Rorsman P, Ramracheya R, Rorsman NJG, Zhang Q. ATP-regulated potassium channels and voltage-gated calcium channels in pancreatic alpha and beta cells: similar functions but reciprocal effects on secretion. Diabetologia 2014; 57:1749-61. [PMID: 24906950 DOI: 10.1007/s00125-014-3279-8] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/16/2014] [Accepted: 04/25/2014] [Indexed: 12/13/2022]
Abstract
Closure of ATP-regulated K(+) channels (K(ATP) channels) plays a central role in glucose-stimulated insulin secretion in beta cells. K(ATP) channels are also highly expressed in glucagon-producing alpha cells, where their function remains unresolved. Under hypoglycaemic conditions, K(ATP) channels are open in alpha cells but their activity is low and only ~1% of that in beta cells. Like beta cells, alpha cells respond to hyperglycaemia with K(ATP) channel closure, membrane depolarisation and stimulation of action potential firing. Yet, hyperglycaemia reciprocally regulates glucagon (inhibition) and insulin secretion (stimulation). Here we discuss how this conundrum can be resolved and how reduced K(ATP) channel activity, via membrane depolarisation, paradoxically reduces alpha cell Ca(2+) entry and glucagon exocytosis. Finally, we consider whether the glucagon secretory defects associated with diabetes can be attributed to impaired K(ATP) channel regulation and discuss the potential for remedial pharmacological intervention using sulfonylureas.
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Affiliation(s)
- Patrik Rorsman
- Radcliffe Department of Medicine, Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Oxford, OX3 7LJ, UK,
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32
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Zhang Q, Chibalina MV, Bengtsson M, Groschner LN, Ramracheya R, Rorsman NJG, Leiss V, Nassar MA, Welling A, Gribble FM, Reimann F, Hofmann F, Wood JN, Ashcroft FM, Rorsman P. Na+ current properties in islet α- and β-cells reflect cell-specific Scn3a and Scn9a expression. J Physiol 2014; 592:4677-96. [PMID: 25172946 PMCID: PMC4253470 DOI: 10.1113/jphysiol.2014.274209] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Mouse pancreatic β- and α-cells are equipped with voltage-gated Na+ currents that inactivate over widely different membrane potentials (half-maximal inactivation (V0.5) at −100 mV and −50 mV in β- and α-cells, respectively). Single-cell PCR analyses show that both α- and β-cells have Nav1.3 (Scn3) and Nav1.7 (Scn9a) α subunits, but their relative proportions differ: β-cells principally express Nav1.7 and α-cells Nav1.3. In α-cells, genetically ablating Scn3a reduces the Na+ current by 80%. In β-cells, knockout of Scn9a lowers the Na+ current by >85%, unveiling a small Scn3a-dependent component. Glucagon and insulin secretion are inhibited in Scn3a−/− islets but unaffected in Scn9a-deficient islets. Thus, Nav1.3 is the functionally important Na+ channel α subunit in both α- and β-cells because Nav1.7 is largely inactive at physiological membrane potentials due to its unusually negative voltage dependence of inactivation. Interestingly, the Nav1.7 sequence in brain and islets is identical and yet the V0.5 for inactivation is >30 mV more negative in β-cells. This may indicate the presence of an intracellular factor that modulates the voltage dependence of inactivation.
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Affiliation(s)
- Quan Zhang
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Margarita V Chibalina
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Martin Bengtsson
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Lukas N Groschner
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Reshma Ramracheya
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Nils J G Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK
| | - Veronika Leiss
- Institut für Pharmakologie und Toxikologie, TU München, Biedersteiner Str. 29, 80802, München, Germany Institut für Pharmakologie und Toxikologie, Eberhard-Karls Universität, Wilhelmstr. 56, 72074, Tübingen, Germany
| | - Mohammed A Nassar
- Molecular Nociception Group, University College London (UCL), Gower Street, London, WC1E 6BT, UK Biomedical Science, University of Sheffield, Sheffield, S10 2TN, UK
| | - Andrea Welling
- Institut für Pharmakologie und Toxikologie, TU München, Biedersteiner Str. 29, 80802, München, Germany
| | - Fiona M Gribble
- Cambridge Institute for Medical Research, University of Cambridge School of Clinical Medicine, Wellcome Trust/MRC Building, Cambridge Biomedical Campus, Hills Road, Cambridge, CB2 0XY, UK
| | - Frank Reimann
- Cambridge Institute for Medical Research, University of Cambridge School of Clinical Medicine, Wellcome Trust/MRC Building, Cambridge Biomedical Campus, Hills Road, Cambridge, CB2 0XY, UK
| | - Franz Hofmann
- Institut für Pharmakologie und Toxikologie, TU München, Biedersteiner Str. 29, 80802, München, Germany FOR 923, Institut für Pharmakologie und Toxikologie, TU München, Biedersteiner Str. 29, 80802, München, Germany
| | - John N Wood
- Molecular Nociception Group, University College London (UCL), Gower Street, London, WC1E 6BT, UK
| | - Frances M Ashcroft
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, OX3 7LJ, UK Department of Neuroscience and Physiology, Sahlgren's Academy, University of Göteborg, Box 430, SE40530, Göteborg, Sweden
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33
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Abstract
The peptide hormone somatostatin (SST) is produced in the brain, the gut, and in δ-cells in pancreatic islets of Langerhans. SST secretion from δ-cells is stimulated by glucose, amino acids, and glucagon-like peptide-1. Exogenous SST strongly inhibits the secretion of the blood glucose-regulating hormones insulin and glucagon from pancreatic β-cells and α-cells, respectively. Endogenous SST secreted from δ-cells is a paracrine regulator of insulin and glucagon secretion, although the exact physiological significance of this regulation is unclear. Secreted SST binds to specific receptors (SSTRs), which are coupled to Gi/o proteins. In both β- and α-cells, activation of SSTRs suppresses hormone secretion by reducing cAMP levels, inhibiting electrical activity, decreasing Ca²⁺ influx through voltage-gated Ca²⁺ channels and directly reducing exocytosis in a Ca²⁺ and cAMP-independent manner. In rodents, β-cells express predominantly SSTR5, whereas α-cells express SSTR2. In human islets, SSTR2 is the dominant receptor in both β- and α-cells, but other isoforms also contribute to the SST effects. Evidence from rodent models suggests that SST secretion from δ-cells is dysregulated in diabetes mellitus, which may contribute to the metabolic disturbances in this disease. SST analogues are currently used for the treatment of hyperinsulinism and other endocrine disorders, including acromegaly and Cushing's syndrome.
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Affiliation(s)
- Matthias Braun
- Alberta Diabetes Institute, Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada.
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34
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Zhang Q, Ramracheya R, Lahmann C, Tarasov A, Bengtsson M, Braha O, Braun M, Brereton M, Collins S, Galvanovskis J, Gonzalez A, Groschner LN, Rorsman NJG, Salehi A, Travers ME, Walker JN, Gloyn AL, Gribble F, Johnson PRV, Reimann F, Ashcroft FM, Rorsman P. Role of KATP channels in glucose-regulated glucagon secretion and impaired counterregulation in type 2 diabetes. Cell Metab 2013; 18:871-82. [PMID: 24315372 PMCID: PMC3851686 DOI: 10.1016/j.cmet.2013.10.014] [Citation(s) in RCA: 166] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Revised: 07/05/2013] [Accepted: 10/31/2013] [Indexed: 01/03/2023]
Abstract
Glucagon, secreted by pancreatic islet α cells, is the principal hyperglycemic hormone. In diabetes, glucagon secretion is not suppressed at high glucose, exacerbating the consequences of insufficient insulin secretion, and is inadequate at low glucose, potentially leading to fatal hypoglycemia. The causal mechanisms remain unknown. Here we show that α cell KATP-channel activity is very low under hypoglycemic conditions and that hyperglycemia, via elevated intracellular ATP/ADP, leads to complete inhibition. This produces membrane depolarization and voltage-dependent inactivation of the Na(+) channels involved in action potential firing that, via reduced action potential height and Ca(2+) entry, suppresses glucagon secretion. Maneuvers that increase KATP channel activity, such as metabolic inhibition, mimic the glucagon secretory defects associated with diabetes. Low concentrations of the KATP channel blocker tolbutamide partially restore glucose-regulated glucagon secretion in islets from type 2 diabetic organ donors. These data suggest that impaired metabolic control of the KATP channels underlies the defective glucose regulation of glucagon secretion in type 2 diabetes.
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Affiliation(s)
- Quan Zhang
- Oxford Centre for Diabetes, Endocrinology, and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, UK
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35
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Low JT, Mitchell JM, Do OH, Bax J, Rawlings A, Zavortink M, Morgan G, Parton RG, Gaisano HY, Thorn P. Glucose principally regulates insulin secretion in mouse islets by controlling the numbers of granule fusion events per cell. Diabetologia 2013; 56:2629-37. [PMID: 23995471 PMCID: PMC3825531 DOI: 10.1007/s00125-013-3019-5] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2013] [Accepted: 07/19/2013] [Indexed: 01/18/2023]
Abstract
AIMS/HYPOTHESIS In dispersed single beta cells the response of each cell to glucose is heterogeneous. In contrast, within an islet, cell-to-cell communication leads to glucose inducing a more homogeneous response. For example, increases in NAD(P)H and calcium are relatively uniform across the cells of the islet. These data suggest that secretion of insulin from single beta cells within an islet should also be relatively homogeneous. The aim of this study was to test this hypothesis by determining the glucose dependence of single-cell insulin responses within an islet. METHODS Two-photon microscopy was used to detect the glucose-induced fusion of single insulin granules within beta cells in intact mouse islets. RESULTS First, we validated our assay and showed that the measures of insulin secretion from whole islets could be explained by the time course and numbers of granule fusion events observed. Subsequent analysis of the patterns of granule fusion showed that cell recruitment is a significant factor, accounting for a fourfold increase from 3 to 20 mmol/l glucose. However, the major factor is the regulation of the numbers of granule fusion events within each cell, which increase ninefold over the range of 3 to 20 mmol/l glucose. Further analysis showed that two types of granule fusion event occur: 'full fusion' and 'kiss and run'. We show that the relative frequency of each type of fusion is independent of glucose concentration and is therefore not a factor in the control of insulin secretion. CONCLUSIONS/INTERPRETATION Within an islet, glucose exerts its main effect through increasing the numbers of insulin granule fusion events within a cell.
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Affiliation(s)
- Jiun T. Low
- School of Biomedical Sciences, University of Queensland, St Lucia, QLD 4072 Australia
| | - Justin M. Mitchell
- School of Biomedical Sciences, University of Queensland, St Lucia, QLD 4072 Australia
| | - Oanh H. Do
- School of Biomedical Sciences, University of Queensland, St Lucia, QLD 4072 Australia
| | - Jacinda Bax
- School of Biomedical Sciences, University of Queensland, St Lucia, QLD 4072 Australia
| | - Alicia Rawlings
- School of Biomedical Sciences, University of Queensland, St Lucia, QLD 4072 Australia
| | - Michael Zavortink
- School of Biomedical Sciences, University of Queensland, St Lucia, QLD 4072 Australia
| | - Garry Morgan
- Institute of Molecular Bioscience, University of Queensland, St Lucia, QLD Australia
| | - Robert G. Parton
- Institute of Molecular Bioscience, University of Queensland, St Lucia, QLD Australia
| | | | - Peter Thorn
- School of Biomedical Sciences, University of Queensland, St Lucia, QLD 4072 Australia
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Abstract
ATP-sensitive potassium channels (K(ATP) channels) link cell metabolism to electrical activity by controlling the cell membrane potential. They participate in many physiological processes but have a particularly important role in systemic glucose homeostasis by regulating hormone secretion from pancreatic islet cells. Glucose-induced closure of K(ATP) channels is crucial for insulin secretion. Emerging data suggest that K(ATP) channels also play a key part in glucagon secretion, although precisely how they do so remains controversial. This Review highlights the role of K(ATP) channels in insulin and glucagon secretion. We discuss how K(ATP) channels might contribute not only to the initiation of insulin release but also to the graded stimulation of insulin secretion that occurs with increasing glucose concentrations. The various hypotheses concerning the role of K(ATP) channels in glucagon release are also reviewed. Furthermore, we illustrate how mutations in K(ATP) channel genes can cause hyposecretion or hypersecretion of insulin, as in neonatal diabetes mellitus and congenital hyperinsulinism, and how defective metabolic regulation of the channel may underlie the hypoinsulinaemia and the hyperglucagonaemia that characterize type 2 diabetes mellitus. Finally, we outline how sulphonylureas, which inhibit K(ATP) channels, stimulate insulin secretion in patients with neonatal diabetes mellitus or type 2 diabetes mellitus, and suggest their potential use to target the glucagon secretory defects found in diabetes mellitus.
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Affiliation(s)
- Frances M Ashcroft
- Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Parks Road, Oxford OX1 3PT, UK
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Cheng-Xue R, Gómez-Ruiz A, Antoine N, Noël LA, Chae HY, Ravier MA, Chimienti F, Schuit FC, Gilon P. Tolbutamide controls glucagon release from mouse islets differently than glucose: involvement of K(ATP) channels from both α-cells and δ-cells. Diabetes 2013; 62:1612-22. [PMID: 23382449 PMCID: PMC3636641 DOI: 10.2337/db12-0347] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We evaluated the role of ATP-sensitive K⁺ (K(ATP)) channels, somatostatin, and Zn²⁺ in the control of glucagon secretion from mouse islets. Switching from 1 to 7 mmol/L glucose inhibited glucagon release. Diazoxide did not reverse the glucagonostatic effect of glucose. Tolbutamide decreased glucagon secretion at 1 mmol/L glucose (G1) but stimulated it at 7 mmol/L glucose (G7). The reduced glucagon secretion produced by high concentrations of tolbutamide or diazoxide, or disruption of K(ATP) channels (Sur1(-/-) mice) at G1 could be inhibited further by G7. Removal of the somatostatin paracrine influence (Sst(-/-) mice or pretreatement with pertussis toxin) strongly increased glucagon release, did not prevent the glucagonostatic effect of G7, and unmasked a marked glucagonotropic effect of tolbutamide. Glucose inhibited glucagon release in the absence of functional K(ATP) channels and somatostatin signaling. Knockout of the Zn²⁺ transporter ZnT8 (ZnT8(-/-) mice) did not prevent the glucagonostatic effect of glucose. In conclusion, glucose can inhibit glucagon release independently of Zn²⁺, K(ATP) channels, and somatostatin. Closure of K(ATP) channels controls glucagon secretion by two mechanisms, a direct stimulation of α-cells and an indirect inhibition via somatostatin released from δ-cells. The net effect on glucagon release results from a balance between both effects.
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Affiliation(s)
- Rui Cheng-Xue
- Pôle d’Endocrinologie, Diabète et Nutrition, Institut de Recherche Expérimentale et Clinique, Université Catholique de Louvain, Brussels, Belgium
| | - Ana Gómez-Ruiz
- Pôle d’Endocrinologie, Diabète et Nutrition, Institut de Recherche Expérimentale et Clinique, Université Catholique de Louvain, Brussels, Belgium
| | - Nancy Antoine
- Pôle d’Endocrinologie, Diabète et Nutrition, Institut de Recherche Expérimentale et Clinique, Université Catholique de Louvain, Brussels, Belgium
| | - Laura A. Noël
- Pôle d’Endocrinologie, Diabète et Nutrition, Institut de Recherche Expérimentale et Clinique, Université Catholique de Louvain, Brussels, Belgium
| | - Hee-Young Chae
- Pôle d’Endocrinologie, Diabète et Nutrition, Institut de Recherche Expérimentale et Clinique, Université Catholique de Louvain, Brussels, Belgium
| | - Magalie A. Ravier
- Institut de Génomique Fonctionnelle, CNRS UMR-5203, INSERM U661, Universités de Montpellier 1 et 2, Montpellier, France
| | | | - Frans C. Schuit
- Gene Expression Unit, Department of Molecular and Cellular Medicine, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Patrick Gilon
- Pôle d’Endocrinologie, Diabète et Nutrition, Institut de Recherche Expérimentale et Clinique, Université Catholique de Louvain, Brussels, Belgium
- Corresponding author: Patrick Gilon,
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Zhao YF, Wang L, Zha D, Qiao L, Lu L, Yu J, Qu P, Sun Q, Qiu J, Chen C. GW9508 inhibits insulin secretion by activating ATP-sensitive potassium channels in rat pancreatic β-cells. J Mol Endocrinol 2013; 51:69-77. [PMID: 23628491 DOI: 10.1530/jme-13-0019] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
GW9508 is an agonist of G protein-coupled receptor 40 (GPR40) that is expressed in pancreatic β-cells and is reported to regulate insulin secretion. However, the effects of GW9508 on pancreatic β-cells in primary culture have not been well investigated. This study measured the acute effects of GW9508 on insulin secretion from rat pancreatic islets in primary culture, and the insulin secretion-related events such as the changes in membrane potential, ATP-sensitive potassium currents (KATP currents), and intracellular Ca(2+) concentrations ([Ca(2+)]i) of rat islet β-cells were also recorded. GW9508 (10-40 μM) did not influence basal insulin levels at 2 mM glucose, but it (above 20 μM) significantly inhibited 5 and 15 mM glucose-stimulated insulin secretion (GSIS). GW9508 did not inhibit insulin secretion stimulated by tolbutamide, the closer of KATP channels. GW9508 activated KATP channels and blocked the membrane depolarization and the increase in [Ca(2+)]i that were stimulated by glucose. GW9508 itself stimulated a transient increase in [Ca(2+)]i, which was fully blocked by depletion of intracellular Ca(2+) stores with thapsigargin or by inhibition of phospholipase C (PLC) activity with U73122. GW9508-induced activation of KATP channels was only partly inhibited by U73122 treatment. In conclusion, although it stimulates a transient release of Ca(2+) from intracellular Ca(2+) stores via activation of PLC, GW9508 inhibits GSIS by activating KATP channels probably in a distal step to GPR40 activation in rat β-cells.
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Affiliation(s)
- Yu-Feng Zhao
- School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia
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39
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Li XN, Herrington J, Petrov A, Ge L, Eiermann G, Xiong Y, Jensen MV, Hohmeier HE, Newgard CB, Garcia ML, Wagner M, Zhang BB, Thornberry NA, Howard AD, Kaczorowski GJ, Zhou YP. The role of voltage-gated potassium channels Kv2.1 and Kv2.2 in the regulation of insulin and somatostatin release from pancreatic islets. J Pharmacol Exp Ther 2012; 344:407-16. [PMID: 23161216 DOI: 10.1124/jpet.112.199083] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The voltage-gated potassium channels Kv2.1 and Kv2.2 are highly expressed in pancreatic islets, yet their contribution to islet hormone secretion is not fully understood. Here we investigate the role of Kv2 channels in pancreatic islets using a combination of genetic and pharmacologic approaches. Pancreatic β-cells from Kv2.1(-/-) mice possess reduced Kv current and display greater glucose-stimulated insulin secretion (GSIS) relative to WT β-cells. Inhibition of Kv2.x channels with selective peptidyl [guangxitoxin-1E (GxTX-1E)] or small molecule (RY796) inhibitors enhances GSIS in isolated wild-type (WT) mouse and human islets, but not in islets from Kv2.1(-/-) mice. However, in WT mice neither inhibitor improved glucose tolerance in vivo. GxTX-1E and RY796 enhanced somatostatin release in isolated human and mouse islets and in situ perfused pancreata from WT and Kv2.1(-/-) mice. Kv2.2 silencing in mouse islets by adenovirus-small hairpin RNA (shRNA) specifically enhanced islet somatostatin, but not insulin, secretion. In mice lacking somatostatin receptor 5, GxTX-1E stimulated insulin secretion and improved glucose tolerance. Collectively, these data show that Kv2.1 regulates insulin secretion in β-cells and Kv2.2 modulates somatostatin release in δ-cells. Development of selective Kv2.1 inhibitors without cross inhibition of Kv2.2 may provide new avenues to promote GSIS for the treatment of type 2 diabetes.
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Affiliation(s)
- Xiaoyan Nina Li
- Department of Metabolic Disorders, Merck Research Laboratories, Rahway, New Jersey, USA
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40
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Hauge-Evans AC, Anderson RL, Persaud SJ, Jones PM. Delta cell secretory responses to insulin secretagogues are not mediated indirectly by insulin. Diabetologia 2012; 55:1995-2004. [PMID: 22526610 DOI: 10.1007/s00125-012-2546-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Accepted: 03/09/2012] [Indexed: 10/28/2022]
Abstract
AIMS/HYPOTHESIS Somatostatin from islet delta cells inhibits insulin and glucagon secretion, but knowledge of the regulation of pancreatic somatostatin release is limited. Some insulin secretagogues stimulate somatostatin secretion, and here we investigated whether delta cell secretory responses are indirectly regulated in a paracrine manner by insulin released from beta cells. METHODS Hormone release from static incubations of primary mouse islets or somatostatin-secreting TGP52 cells was measured by RIA. mRNA expression was assessed by RT-PCR. RESULTS Glucose and a range of other physiological and pharmacological agents stimulated insulin and somatostatin release, and insulin receptor mRNA was expressed in islets, MIN6 beta cells and TGP52 cells. However, exogenous insulin did not modulate basal or glucose-induced somatostatin secretion from islets, nor did pre-incubation with an antibody against the insulin receptor or with the insulin receptor tyrosine kinase inhibitor, HNMPA(AM)(3). Glucose and tolbutamide stimulated somatostatin release from TGP52 cells, whereas a range of receptor-operating agents had no effect, the latter being consistent with a lack of corresponding receptor mRNA expression in these cells. Parasympathetic activation stimulated insulin, but inhibited somatostatin release from mouse islets in accordance with differences in muscarinic receptor mRNA expression in islets, MIN6 and TGP52 cells. The inhibitory effect on somatostatin secretion was reversed by pertussis toxin or the muscarinic receptor 2 antagonist, methoctramine. CONCLUSIONS/INTERPRETATIONS A number of insulin secretagogues have analogous effects on insulin and somatostatin release, but this similarity of response is not mediated by an indirect, paracrine action of insulin on delta cells.
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Affiliation(s)
- A C Hauge-Evans
- Diabetes Research Group, Division of Diabetes and Nutritional Sciences, School of Medicine, King's College London, Guy's Campus, London Bridge, London SE1 1UL, UK.
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41
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Wu ZY, Zhu LJ, Zou N, Bombek LK, Shao CY, Wang N, Wang XX, Liang L, Xia J, Rupnik M, Shen Y. AMPA receptors regulate exocytosis and insulin release in pancreatic β cells. Traffic 2012; 13:1124-39. [PMID: 22540213 DOI: 10.1111/j.1600-0854.2012.01373.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2011] [Revised: 04/25/2012] [Accepted: 04/27/2012] [Indexed: 01/06/2023]
Abstract
Ionotropic glutamate receptors (iGluRs) are expressed in islets and insulinoma cells and involved in insulin secretion. However, the exact roles that iGluRs play in β cells remain unclear. Here, we demonstrated that GluR2-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) were expressed in mouse β cells. Glutamate application increased both cytosolic calcium and the number of docked insulin-containing granules, which resulted in augmentation of depolarization-induced exocytosis and high-glucose-stimulated insulin release. While glutamate application directly depolarized β cells, it also induced an enormous depolarization when K(ATP) channels were available. Glutamate application reduced the conductance of K(ATP) channels and increased voltage oscillations. Moreover, actions of AMPARs were absent in Kir6.2 knock-out mice. The effects of AMPARs on K(ATP) channels were mediated by cytosolic cGMP. Taken together, our experiments uncovered a novel mechanism by which AMPARs participate in insulin release.
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Affiliation(s)
- Zhen-Yong Wu
- Department of Neurobiology, Key Laboratory of Medical Neurobiology of Ministry of Health, Zhejiang Province Key Laboratory of Neurobiology, Zhejiang University School of Medicine, Hangzhou, Zhejiang, 310058, P. R. China
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42
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Koh DS, Cho JH, Chen L. Paracrine interactions within islets of Langerhans. J Mol Neurosci 2012; 48:429-40. [PMID: 22528452 DOI: 10.1007/s12031-012-9752-2] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2012] [Accepted: 03/12/2012] [Indexed: 01/05/2023]
Abstract
Glucose supply fluctuates between meal and fasting periods and its consumption by the body varies greatly depending on bodily metabolism. Pancreatic islets of Langerhans secrete various endocrine hormones including insulin and glucagon to keep blood glucose level relatively constant. Additionally, islet hormones regulate activity of neighboring cells as local autocrine or paracrine modulators. Moreover, islet cells release neurotransmitters such as glutamate and γ-aminobutyric acid (GABA) to gain more precise regulation of hormones release kinetics. Excitatory glutamate is co-released with glucagon from α-cells and activates glutamate receptors in the neighboring cells. GABA released from β-cells was shown to inhibit α-cells but to activate β-cells by acting GABA(A) receptors. This review summarizes the recent progress in understanding the paracrine/autocrine interactions in islets.
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Affiliation(s)
- Duk-Su Koh
- University of Washington, Seattle, WA, USA.
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43
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Regulation of calcium in pancreatic α- and β-cells in health and disease. Cell Calcium 2011; 51:300-8. [PMID: 22177710 PMCID: PMC3334273 DOI: 10.1016/j.ceca.2011.11.006] [Citation(s) in RCA: 169] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2011] [Revised: 11/10/2011] [Accepted: 11/17/2011] [Indexed: 12/15/2022]
Abstract
The glucoregulatory hormones insulin and glucagon are released from the β- and α-cells of the pancreatic islets. In both cell types, secretion is secondary to firing of action potentials, Ca2+-influx via voltage-gated Ca2+-channels, elevation of [Ca2+]i and initiation of Ca2+-dependent exocytosis. Here we discuss the mechanisms that underlie the reciprocal regulation of insulin and glucagon secretion by changes in plasma glucose, the roles played by different types of voltage-gated Ca2+-channel present in α- and β-cells and the modulation of hormone secretion by Ca2+-dependent and -independent processes. We also consider how subtle changes in Ca2+-signalling may have profound impact on β-cell performance and increase risk of developing type-2 diabetes.
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44
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Rorsman P, Eliasson L, Kanno T, Zhang Q, Gopel S. Electrophysiology of pancreatic β-cells in intact mouse islets of Langerhans. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2011; 107:224-35. [PMID: 21762719 DOI: 10.1016/j.pbiomolbio.2011.06.009] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2011] [Accepted: 06/21/2011] [Indexed: 10/18/2022]
Abstract
When exposed to intermediate glucose concentrations (6-16 mol/l), pancreatic β-cells in intact islets generate bursts of action potentials (superimposed on depolarised plateaux) separated by repolarised electrically silent intervals. First described more than 40 years ago, these oscillations have continued to intrigue β-cell electrophysiologists. To date, most studies of β-cell ion channels have been performed on isolated cells maintained in tissue culture (that do not burst). Here we will review the electrophysiological properties of β-cells in intact, freshly isolated, mouse pancreatic islets. We will consider the role of ATP-regulated K⁺-channels (K(ATP)-channels), small-conductance Ca²⁺-activated K⁺-channels and voltage-gated Ca²⁺-channels in the generation of the bursts. Our data indicate that K(ATP)-channels not only constitute the glucose-regulated resting conductance in the β-cell but also provide a variable K⁺-conductance that influence the duration of the bursts of action potentials and the silent intervals. We show that inactivation of the voltage-gated Ca²⁺-current is negligible at voltages corresponding to the plateau potential and consequently unlikely to play a major role in the termination of the burst. Finally, we propose a model for glucose-induced β-cell electrical activity based on observations made in intact pancreatic islets.
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Affiliation(s)
- Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Oxford OX37LJ, UK.
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Rapposelli S. Novel adenosine 5'-triphosphate-sensitive potassium channel ligands: a patent overview (2005-2010). Expert Opin Ther Pat 2011; 21:355-79. [PMID: 21269236 DOI: 10.1517/13543776.2011.553601] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
INTRODUCTION ATP-sensitive potassium channels are important metabolic regulators that link cellular metabolism to excitability. Their wide distribution in various tissues and organs makes them significant and topical targets in a large number of diseases. AREAS COVERED This review summarizes the current understanding of the molecular biology and pharmacology of K(ATP) channels, and the pathological states that result from aberrant expression or function of these proteins. In particular, relevant research, patents and patent applications of the past 5 years are discussed. EXPERT OPINION The tissue-specific K(ATP) channel modulation reflects an early discovery stage in drug design. The wide distribution of K(ATP) channels lets us consider them as valid targets for several pathologies, but on other hand the ubiquitous nature is a relevant drawback in developing an effective therapy because of the onset of side effects related to the lack of selectivity. On this basis, further investigations on both the structures and the localization of each receptor subtype should be carried out either exploring the structure-activity relationship of the already existing K(ATP) ligands or developing new selective fluorescent probes. To date, this research area still strives to design new tissue-targeted ligands that could pave the way to the development of innovative and effective drugs for clinical use.
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Affiliation(s)
- Simona Rapposelli
- Dipartimento di Scienze Farmaceutiche - Università di Pisa, Via Bonanno, 6, 56126 Pisa, Italy.
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46
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Farhy LS, McCall AL. Models of glucagon secretion, their application to the analysis of the defects in glucagon counterregulation and potential extension to approximate glucagon action. J Diabetes Sci Technol 2010; 4:1345-56. [PMID: 21129329 PMCID: PMC3005044 DOI: 10.1177/193229681000400608] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
This review analyzes an interdisciplinary approach to the pancreatic endocrine network-like relationships that control glucagon secretion and glucagon counterregulation (GCR). Using in silico studies, we show that a pancreatic feedback network that brings together several explicit interactions between islet peptides and blood glucose reproduces the normal GCR axis and explains its impairment in diabetes. An α-cell auto-feedback loop drives glucagon pulsatility and mediates triggering of GCR by hypoglycemia by a rapid switch-off of β-cell signals. The auto-feedback explains the enhancement of defective GCR in β-cell deficiency by a switch-off of signals in the pancreas that suppress α cells. Our models also predict that reduced β-cell activity decreases and delays the GCR. A key application of our models is the in silico simulation and testing of possible scenarios to repair defective GCR in β-cell deficiency. In particular, we predict that partial suppression of hyperglucagonemia may repair the impaired GCR. We also outline how the models can be extended and tested using human data to become a part of a larger construct including the regulation of the hepatic glucose output by the pancreas, circulating glucose, and incretins. In conclusion, a model of the normal GCR control mechanisms and their dysregulation in insulin-deficient diabetes is proposed and partially validated. The model components are clinically measurable, which permits its application to the study of the abnormalities of the human endocrine pancreas and their role in the progression of many diseases, including diabetes, metabolic syndrome, polycystic ovary syndrome, and others. It may also be used to examine therapeutic responses.
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Affiliation(s)
- Leon S Farhy
- Department of Medicine, Center for Biomathematical Technology, University of Virginia, Charlottesville, Virginia 22908, USA.
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47
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Spigelman AF, Dai X, MacDonald PE. Voltage-dependent K(+) channels are positive regulators of alpha cell action potential generation and glucagon secretion in mice and humans. Diabetologia 2010; 53:1917-26. [PMID: 20446079 DOI: 10.1007/s00125-010-1759-z] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Accepted: 03/23/2010] [Indexed: 01/22/2023]
Abstract
AIMS/HYPOTHESIS The regulation of glucagon secretion from alpha cells is poorly understood. Since action potential firing at low glucose is required for glucagon secretion, we hypothesised that voltage-dependent K(+) (Kv) currents limit glucagon secretion under these conditions, similarly to their role in insulin secretion. METHODS Kv currents and action potential firing of mouse and human alpha cells, identified by immunostaining, were examined by whole-cell patch-clamp. Glucagon secretion from mouse and human islets was measured by ELISA. RESULTS Kv current density was 35% larger in alpha than in beta cells. Alpha cell Kv channels were sensitive to block by tetraethylammonium (TEA) and 4-aminopyridine. Surprisingly, Kv channel inhibition reduced glucagon release to the same extent as glucose. Robust action potential firing was observed in beta cells when ATP-sensitive K(+) channels were closed, but in alpha cells a negative current (-8 pA) injection was required for action potential firing. TEA (0.5 mmol/l) impaired alpha cell action potential firing, which could be restored by further hyperpolarising current injection (-16 pA). Kv currents were more sensitive to the Kv2 inhibitor stromatoxin (100 nmol/l) in mouse (80%) than in human (45%) alpha cells. Finally, the maxi-K (BK) channel inhibitor iberiotoxin (100 nmol/l) blocked 55% of the current in human alpha cells and inhibited glucagon release from human islets. CONCLUSIONS/INTERPRETATION Kv currents in alpha cells are positive regulators of glucagon secretion. These currents, mediated by Kv2 and BK channels, limit membrane depolarisation, and prevent inactivation of alpha cell action potentials and suppression of glucagon release.
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Affiliation(s)
- A F Spigelman
- Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
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Li W, Shi YH, Yang RL, Cui J, Xiao Y, Le GW. Reactive oxygen species serve as signals mediating glucose-stimulated somatostatin secretion from cultured rat gastric primary D-cells. Free Radic Res 2010; 44:614-23. [PMID: 20370561 DOI: 10.3109/10715761003713549] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Somatostatin plays an important role in glucose homeostasis. It is normally secreted in response to glucose and ATP generation is believed to be the key transduction signal of glucose-stimulated somatostatin secretion (GSSS). However, in the present study, in cultured rat gastric primary D-cells, GSSS was accompanied by increases in cellular reactive oxygen species (ROS). GSSS is dependent on the cellular ROS and independently of the ATP production linked to glucose metabolism. The antioxidant, alpha-lipoic acid or catalase inhibitor, 3-aminotriazole can influence the intracellular calcium concentration and abolish or further elevate GSSS. It is suggested that ROS production may serve as a signal modulating the necessary Ca(2+) recruitment for GSSS. Since somatostatin is thought to exert broad regulatory functions on gastrointestinal physiology and nutrient intake, the interaction with ROS may lead to potential targets for mediating nutrition and energy homeostasis.
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Affiliation(s)
- Wu Li
- State Key Lab of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu Province, PR China
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49
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Jacobson DA, Mendez F, Thompson M, Torres J, Cochet O, Philipson LH. Calcium-activated and voltage-gated potassium channels of the pancreatic islet impart distinct and complementary roles during secretagogue induced electrical responses. J Physiol 2010; 588:3525-37. [PMID: 20643768 DOI: 10.1113/jphysiol.2010.190207] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Glucose-induced β-cell action potential (AP) repolarization is regulated by potassium efflux through voltage gated (Kv) and calcium activated (K(Ca)) potassium channels. Thus, ablation of the primary Kv channel of the β-cell, Kv2.1, causes increased AP duration. However, Kv2.1(-/-) islet electrical activity still remains sensitive to the potassium channel inhibitor tetraethylammonium. Therefore, we utilized Kv2.1(-/-) islets to characterize Kv and K(Ca) channels and their respective roles in modulating the β-cell AP. The remaining Kv current present in Kv2.1(-/-) β-cells is inhibited with 5 μM CP 339818. Inhibition of the remaining Kv current in Kv2.1(-/-) mouse β-cells increased AP firing frequency by 39.6% but did not significantly enhance glucose stimulated insulin secretion (GSIS). The modest regulation of islet AP frequency by CP 339818 implicates other K(+) channels, possibly K(Ca) channels, in regulating AP repolarization. Blockade of the K(Ca) channel BK with slotoxin increased β-cell AP amplitude by 28.2%, whereas activation of BK channels with isopimaric acid decreased β-cell AP amplitude by 30.6%. Interestingly, the K(Ca) channel SK significantly contributes to Kv2.1(-/-) mouse islet AP repolarization. Inhibition of SK channels decreased AP firing frequency by 66% and increased AP duration by 67% only when Kv2.1 is ablated or inhibited and enhanced GSIS by 2.7-fold. Human islets also express SK3 channels and their β-cell AP frequency is significantly accelerated by 4.8-fold with apamin. These results uncover important repolarizing roles for both Kv and K(Ca) channels and identify distinct roles for SK channel activity in regulating calcium- versus sodium-dependent AP firing.
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Affiliation(s)
- David A Jacobson
- Deparment of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232-0615, USA.
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Drews G, Krippeit-Drews P, Düfer M. Electrophysiology of islet cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 654:115-63. [PMID: 20217497 DOI: 10.1007/978-90-481-3271-3_7] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Stimulus-Secretion Coupling (SSC) of pancreatic islet cells comprises electrical activity. Changes of the membrane potential (V(m)) are regulated by metabolism-dependent alterations in ion channel activity. This coupling is best explored in beta-cells. The effect of glucose is directly linked to mitochondrial metabolism as the ATP/ADP ratio determines the open probability of ATP-sensitive K(+) channels (K(ATP) channels). Nucleotide sensitivity and concentration in the direct vicinity of the channels are controlled by several factors including phospholipids, fatty acids, and kinases, e.g., creatine and adenylate kinase. Closure of K(ATP) channels leads to depolarization of beta-cells via a yet unknown depolarizing current. Ca(2+) influx during action potentials (APs) results in an increase of the cytosolic Ca(2+) concentration ([Ca(2+)](c)) that triggers exocytosis. APs are elicited by the opening of voltage-dependent Na(+) and/or Ca(2+) channels and repolarized by voltage- and/or Ca(2+)-dependent K(+) channels. At a constant stimulatory glucose concentration APs are clustered in bursts that are interrupted by hyperpolarized interburst phases. Bursting electrical activity induces parallel fluctuations in [Ca(2+)](c) and insulin secretion. Bursts are terminated by I(Kslow) consisting of currents through Ca(2+)-dependent K(+) channels and K(ATP) channels. This review focuses on structure, characteristics, physiological function, and regulation of ion channels in beta-cells. Information about pharmacological drugs acting on K(ATP) channels, K(ATP) channelopathies, and influence of oxidative stress on K(ATP) channel function is provided. One focus is the outstanding significance of L-type Ca(2+) channels for insulin secretion. The role of less well characterized beta-cell channels including voltage-dependent Na(+) channels, volume sensitive anion channels (VSACs), transient receptor potential (TRP)-related channels, and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels is discussed. A model of beta-cell oscillations provides insight in the interplay of the different channels to induce and maintain electrical activity. Regulation of beta-cell electrical activity by hormones and the autonomous nervous system is discussed. alpha- and delta-cells are also equipped with K(ATP) channels, voltage-dependent Na(+), K(+), and Ca(2+) channels. Yet the SSC of these cells is less clear and is not necessarily dependent on K(ATP) channel closure. Different ion channels of alpha- and delta-cells are introduced and SSC in alpha-cells is described in special respect of paracrine effects of insulin and GABA secreted from beta-cells.
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Affiliation(s)
- Gisela Drews
- Institute of Pharmacy, Department of Pharmacology and Clinical Pharmacy, University of Tübingen, 72076 Tübingen, Germany.
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