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Piro A, Luo Y, Zhang Z, Ye W, Kang F, Li X, Wang Y, Dai FF, Gaisano HY, Rocheleau JV, Prentice KJ, Wheeler MB. Beta cell specific ZnT8 gene deficiency and resulting loss in zinc content significantly improve insulin secretion. Mol Cell Endocrinol 2024:112376. [PMID: 39321953 DOI: 10.1016/j.mce.2024.112376] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/21/2024] [Revised: 09/06/2024] [Accepted: 09/22/2024] [Indexed: 09/27/2024]
Abstract
Zinc transporter 8 (ZnT8) is highly expressed in pancreatic beta cells, localizes to insulin secretory granules (ISG), and regulates zinc content. ZnT8 gene polymorphisms have revealed a relationship between ZnT8 activity and type 2 diabetes (T2D) risk, however, the role of beta-cell ZnT8 is not well understood. A beta cell specific ZnT8 knockout (ZnT8 BKO) mouse model was investigated. ZnT8 BKO islets showed significantly reduced ZnT8 gene expression and reduced zinc content. In vivo, ZnT8 BKO mice compared to controls displayed significantly elevated plasma insulin levels and improved glucose tolerance following acute insulin resistance induced via S961. Glucose stimulated insulin secretion from isolated ZnT8 BKO pancreatic islets revealed enhanced insulin secretion capacity. The difference in insulin secretion between ZnT8 BKO and control islets was negated upon zinc supplementation, and the inhibitory effect was confirmed in human islets. These results indicate that the loss of ZnT8 activity, and accompanying reduced cellular zinc are associated with increased insulin secretion capacity. The reduction in secreted insulin content upon zinc supplementation in ZnT8 BKO islets suggests that ISG-released zinc normally tempers insulin secretion.
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Affiliation(s)
- Anthony Piro
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Yihan Luo
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Ziyi Zhang
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada; Department of Endocrinology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang, China
| | - Wenyue Ye
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Fei Kang
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Xie Li
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Yufeng Wang
- Advanced Diagnostics, Toronto General Hospital Research Institute, Toronto, ON M5G 1L7, Canada; Institute of Biomedical Engineering, University of Toronto, Toronto, ON M5S 3G9, Canada
| | - Feihan F Dai
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Herbert Y Gaisano
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Jonathan V Rocheleau
- Department of Endocrinology, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou, Zhejiang, China; Advanced Diagnostics, Toronto General Hospital Research Institute, Toronto, ON M5G 1L7, Canada
| | - Kacey J Prentice
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Michael B Wheeler
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
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2
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Fujii T, Shimizu T, Kaji Y, Katoh M, Sakai H. Activation of mouse Otop3 proton channels by Zn2+. Biochem Biophys Res Commun 2023; 658:55-61. [PMID: 37023615 DOI: 10.1016/j.bbrc.2023.03.066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Accepted: 03/28/2023] [Indexed: 03/31/2023]
Abstract
Otopetrins (Otop1-Otop3) belong to a newly identified family of proton (H+) channels activated by extracellular acidification. Here, we found that Zn2+ activates the mouse Otop3 (mOtop3) proton channels by using electrophysiological patch-clamp techniques. In mOtop3-expressing human embryonic kidney HEK293T cells, a biphasic inward mOtop3 H+ current comprising a fast transient current followed by a sustained current was observed upon extracellular acidification at pH 5.0. No significant activation of the mOtop3 channel was observed at pH 6.5 and 7.4, but interestingly, Zn2+ dose-dependently induced a sustained activation of mOtop3 under these pH conditions. Increasing the Zn2+ concentration had no effect on the reversal potential of the channel currents, suggesting that Zn2+ does not permeate through the mOtop3. The activation of the mOtop3 channel was specific to Zn2+ among divalent metal cations. Our findings reveal a novel modulatory mechanism of mOtop3 proton channels by Zn2+.
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3
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ZnT8 loss-of-function accelerates functional maturation of hESC-derived β cells and resists metabolic stress in diabetes. Nat Commun 2022; 13:4142. [PMID: 35842441 PMCID: PMC9288460 DOI: 10.1038/s41467-022-31829-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Accepted: 07/04/2022] [Indexed: 12/21/2022] Open
Abstract
Human embryonic stem cell-derived β cells (SC-β cells) hold great promise for treatment of diabetes, yet how to achieve functional maturation and protect them against metabolic stresses such as glucotoxicity and lipotoxicity remains elusive. Our single-cell RNA-seq analysis reveals that ZnT8 loss of function (LOF) accelerates the functional maturation of SC-β cells. As a result, ZnT8 LOF improves glucose-stimulated insulin secretion (GSIS) by releasing the negative feedback of zinc inhibition on insulin secretion. Furthermore, we demonstrate that ZnT8 LOF mutations endow SC-β cells with resistance to lipotoxicity/glucotoxicity-triggered cell death by alleviating endoplasmic reticulum (ER) stress through modulation of zinc levels. Importantly, transplantation of SC-β cells with ZnT8 LOF into mice with preexisting diabetes significantly improves glycemia restoration and glucose tolerance. These findings highlight the beneficial effect of ZnT8 LOF on the functional maturation and survival of SC-β cells that are useful as a potential source for cell replacement therapies. Immature function and fragility hinder application of hESC-derived β cells (SC-β cell) for diabetes cell therapy. Here, the authors identify ZnT8 as a gene editing target to enhance the insulin secretion and cell survival under metabolic stress by abolishing zinc transport in SC-β cells.
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4
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Ghazvini Zadeh EH, Huang Z, Xia J, Li D, Davidson HW, Li WH. ZIGIR, a Granule-Specific Zn 2+ Indicator, Reveals Human Islet α Cell Heterogeneity. Cell Rep 2021; 32:107904. [PMID: 32668245 DOI: 10.1016/j.celrep.2020.107904] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 05/04/2020] [Accepted: 06/23/2020] [Indexed: 02/07/2023] Open
Abstract
Numerous mammalian cells contain abundant Zn2+ in their secretory granules, yet available Zn2+ sensors lack the desired specificity and sensitivity for imaging granular Zn2+. We developed a fluorescent zinc granule indicator, ZIGIR, that possesses numerous desired properties for live cell imaging, including >100-fold fluorescence enhancement, membrane permeability, and selective enrichment to acidic granules. The combined advantages endow ZIGIR with superior sensitivity and specificity for imaging granular Zn2+. ZIGIR enables separation of heterogenous β cells based on their insulin content and sorting of mouse islets into pure α cells and β cells. In human islets, ZIGIR facilitates sorting of endocrine cells into highly enriched α cells and β cells, reveals unexpectedly high Zn2+ activity in the somatostatin granule of some δ cells, and uncovers variation in the glucagon content among human α cells. We expect broad applications of ZIGIR for studying Zn2+ biology and Zn2+-rich secretory granules and for engineering β cells with high insulin content for treating diabetes.
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Affiliation(s)
- Ebrahim H Ghazvini Zadeh
- Departments of Cell Biology and Biochemistry, University of Texas Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX 75390-9039, USA
| | - ZhiJiang Huang
- Departments of Cell Biology and Biochemistry, University of Texas Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX 75390-9039, USA
| | - Jing Xia
- Departments of Cell Biology and Biochemistry, University of Texas Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX 75390-9039, USA; Department of Biological Sciences, The University of Texas at Dallas, Richardson, TX, USA
| | - Daliang Li
- Departments of Cell Biology and Biochemistry, University of Texas Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX 75390-9039, USA
| | - Howard W Davidson
- Barbara Davis Center for Diabetes, University of Colorado Denver Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Wen-Hong Li
- Departments of Cell Biology and Biochemistry, University of Texas Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX 75390-9039, USA.
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5
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Barragán-Álvarez CP, Padilla-Camberos E, Díaz NF, Cota-Coronado A, Hernández-Jiménez C, Bravo-Reyna CC, Díaz-Martínez NE. Loss of Znt8 function in diabetes mellitus: risk or benefit? Mol Cell Biochem 2021; 476:2703-2718. [PMID: 33666829 DOI: 10.1007/s11010-021-04114-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Accepted: 02/18/2021] [Indexed: 12/13/2022]
Abstract
The zinc transporter 8 (ZnT8) plays an essential role in zinc homeostasis inside pancreatic β cells, its function is related to the stabilization of insulin hexameric form. Genome-wide association studies (GWAS) have established a positive and negative relationship of ZnT8 variants with type 2 diabetes mellitus (T2DM), exposing a dual and controversial role. The first hypotheses about its role in T2DM indicated a higher risk of developing T2DM for loss of function; nevertheless, recent GWAS of ZnT8 loss-of-function mutations in humans have shown protection against T2DM. With regard to the ZnT8 role in T2DM, most studies have focused on rodent models and common high-risk variants; however, considerable differences between human and rodent models have been found and the new approaches have included lower-frequency variants as a tool to clarify gene functions, allowing a better understanding of the disease and offering possible therapeutic targets. Therefore, this review will discuss the physiological effects of the ZnT8 variants associated with a major and lower risk of T2DM, emphasizing the low- and rare-frequency variants.
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Affiliation(s)
- Carla P Barragán-Álvarez
- Biotecnología Médica y Farmacéutica, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, Guadalajara, Mexico
| | - Eduardo Padilla-Camberos
- Biotecnología Médica y Farmacéutica, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, Guadalajara, Mexico
| | - Nestor F Díaz
- Departamento de Fisiología y Desarrollo Celular, Instituto Nacional de Perinatología, Mexico City, Mexico
| | - Agustín Cota-Coronado
- Biotecnología Médica y Farmacéutica, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, Guadalajara, Mexico
| | - Claudia Hernández-Jiménez
- Departamento de Cirugía Experimental, Instituto Nacional de Enfermedades Respiratorias Ismael Cosío Villegas, Mexico City, Mexico
| | - Carlos C Bravo-Reyna
- Departamento de Cirugía Experimental, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico City, Mexico
| | - Nestor E Díaz-Martínez
- Biotecnología Médica y Farmacéutica, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, Guadalajara, Mexico.
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6
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Shen Z, Haragopal H, Li YV. Zinc modulates synaptic transmission by differentially regulating synaptic glutamate homeostasis in hippocampus. Eur J Neurosci 2020; 52:3710-3722. [PMID: 32302450 DOI: 10.1111/ejn.14749] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Revised: 02/29/2020] [Accepted: 04/10/2020] [Indexed: 12/27/2022]
Abstract
A subset of presynaptic glutamatergic vesicles in the brain co-releases zinc (Zn2+ ) with glutamate into the synapse. However, the role of synaptically released Zn2+ is still under investigation. Here, we studied the effect of Zn2+ on glutamate homeostasis by measuring the evoked extracellular glutamate level (EGL) and the probability of evoked action potential (PEAP ) at the Zn2+ -containing or zincergic mossy fiber-CA3 synapses of the rat hippocampus. We found that the application of Zn2+ (ZnCl2 ) exerted bidirectional effects on both EGL and PEAP : facilitatory at low concentration (~1 µM) while repressive at high concentration (~50 µM). To determine the action of endogenous Zn2+ , we also used extracellular Zn2+ chelator to remove the synaptically released Zn2+ . Zn2+ chelation reduced both EGL and PEAP , suggesting that endogenous Zn2+ has mainly a facilitative role in glutamate secretion on physiological condition. We revealed that calcium/calmodulin-dependent protein kinase II was integral to the mechanism by which Zn2+ facilitated the release of glutamate. Moreover, a glutamate transporter was the molecular entity for the action of Zn2+ on glutamate uptake by which Zn2+ decreases glutamate availability. Taken together, we show a novel action of Zn2+ , which is to biphasically regulate glutamate homeostasis via Zn2+ concentration-dependent synaptic facilitation and depression. Thus, co-released Zn2+ is physiologically important for enhancing weak stimulation, but potentially mitigates excessive stimulation to keep synaptic transmission within optimal physiological range.
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Affiliation(s)
- Zhijun Shen
- Departments of Biological Sciences and Biomedical Sciences, Ohio University, Athens, OH, USA
| | - Hariprakash Haragopal
- Departments of Biological Sciences and Biomedical Sciences, Ohio University, Athens, OH, USA
| | - Yang V Li
- Departments of Biological Sciences and Biomedical Sciences, Ohio University, Athens, OH, USA
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7
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Hartig SM, Cox AR. Paracrine signaling in islet function and survival. J Mol Med (Berl) 2020; 98:451-467. [PMID: 32067063 DOI: 10.1007/s00109-020-01887-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Revised: 02/05/2020] [Accepted: 02/11/2020] [Indexed: 02/06/2023]
Abstract
The pancreatic islet is a dense cellular network comprised of several cell types with endocrine function vital in the control of glucose homeostasis, metabolism, and feeding behavior. Within the islet, endocrine hormones also form an intricate paracrine network with supportive cells (endothelial, neuronal, immune) and secondary signaling molecules regulating cellular function and survival. Modulation of these signals has potential consequences for diabetes development, progression, and therapeutic intervention. Beta cell loss, reduced endogenous insulin secretion, and dysregulated glucagon secretion are hallmark features of both type 1 and 2 diabetes that not only impact systemic regulation of glucose, but also contribute to the function and survival of cells within the islet. Advancing research and technology have revealed new islet biology (cellular identity and transcriptomes) and identified previously unrecognized paracrine signals and mechanisms (somatostatin and ghrelin paracrine actions), while shifting prior views of intraislet communication. This review will summarize the paracrine signals regulating islet endocrine function and survival, the disruption and dysfunction that occur in diabetes, and potential therapeutic targets to preserve beta cell mass and function.
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Affiliation(s)
- Sean M Hartig
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX, 77030, USA
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, 77030, USA
| | - Aaron R Cox
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX, 77030, USA.
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8
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Dwivedi OP, Lehtovirta M, Hastoy B, Chandra V, Krentz NAJ, Kleiner S, Jain D, Richard AM, Abaitua F, Beer NL, Grotz A, Prasad RB, Hansson O, Ahlqvist E, Krus U, Artner I, Suoranta A, Gomez D, Baras A, Champon B, Payne AJ, Moralli D, Thomsen SK, Kramer P, Spiliotis I, Ramracheya R, Chabosseau P, Theodoulou A, Cheung R, van de Bunt M, Flannick J, Trombetta M, Bonora E, Wolheim CB, Sarelin L, Bonadonna RC, Rorsman P, Davies B, Brosnan J, McCarthy MI, Otonkoski T, Lagerstedt JO, Rutter GA, Gromada J, Gloyn AL, Tuomi T, Groop L. Loss of ZnT8 function protects against diabetes by enhanced insulin secretion. Nat Genet 2019; 51:1596-1606. [PMID: 31676859 PMCID: PMC6858874 DOI: 10.1038/s41588-019-0513-9] [Citation(s) in RCA: 91] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2018] [Accepted: 09/13/2019] [Indexed: 12/30/2022]
Abstract
A rare loss-of-function allele p.Arg138* in SLC30A8 encoding the zinc transporter 8 (ZnT8), which is enriched in Western Finland, protects against type 2 diabetes (T2D). We recruited relatives of the identified carriers and showed that protection was associated with better insulin secretion due to enhanced glucose responsiveness and proinsulin conversion, particularly when compared with individuals matched for the genotype of a common T2D-risk allele in SLC30A8, p.Arg325. In genome-edited human induced pluripotent stem cell (iPSC)-derived β-like cells, we establish that the p.Arg138* allele results in reduced SLC30A8 expression due to haploinsufficiency. In human β cells, loss of SLC30A8 leads to increased glucose responsiveness and reduced KATP channel function similar to isolated islets from carriers of the T2D-protective allele p.Trp325. These data position ZnT8 as an appealing target for treatment aimed at maintaining insulin secretion capacity in T2D.
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Affiliation(s)
- Om Prakash Dwivedi
- Institute for Molecular Medicine Finland, Helsinki University, Helsinki, Finland
| | - Mikko Lehtovirta
- Institute for Molecular Medicine Finland, Helsinki University, Helsinki, Finland
| | - Benoit Hastoy
- Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford, UK
| | - Vikash Chandra
- Stem Cells and Metabolism Research Program and Biomedicum Stem Cell Centre, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Nicole A J Krentz
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | | | - Deepak Jain
- Department of Experimental Medical Science, Lund University, Lund, Sweden
| | | | - Fernando Abaitua
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Nicola L Beer
- Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford, UK
| | - Antje Grotz
- Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford, UK
| | - Rashmi B Prasad
- Lund University Diabetes Centre, Department of Clinical Sciences, Lund University, Skåne University Hospital, Malmö, Sweden
| | - Ola Hansson
- Institute for Molecular Medicine Finland, Helsinki University, Helsinki, Finland
- Lund University Diabetes Centre, Department of Clinical Sciences, Lund University, Skåne University Hospital, Malmö, Sweden
| | - Emma Ahlqvist
- Lund University Diabetes Centre, Department of Clinical Sciences, Lund University, Skåne University Hospital, Malmö, Sweden
| | - Ulrika Krus
- Lund University Diabetes Centre, Department of Clinical Sciences, Lund University, Skåne University Hospital, Malmö, Sweden
| | - Isabella Artner
- Lund University Diabetes Centre, Department of Clinical Sciences, Lund University, Skåne University Hospital, Malmö, Sweden
| | - Anu Suoranta
- Institute for Molecular Medicine Finland, Helsinki University, Helsinki, Finland
| | | | - Aris Baras
- Regeneron Pharmaceuticals, Tarrytown, NY, USA
| | - Benoite Champon
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Anthony J Payne
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Daniela Moralli
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Soren K Thomsen
- Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford, UK
| | - Philipp Kramer
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Ioannis Spiliotis
- Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford, UK
| | - Reshma Ramracheya
- Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford, UK
| | - Pauline Chabosseau
- Section of Cell Biology, Department of Medicine, Imperial College London, Imperial Centre for Translational and Experimental Medicine, Hammersmith, Hospital, London, UK
| | - Andria Theodoulou
- Section of Cell Biology, Department of Medicine, Imperial College London, Imperial Centre for Translational and Experimental Medicine, Hammersmith, Hospital, London, UK
| | - Rebecca Cheung
- Section of Cell Biology, Department of Medicine, Imperial College London, Imperial Centre for Translational and Experimental Medicine, Hammersmith, Hospital, London, UK
| | - Martijn van de Bunt
- Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford, UK
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Jason Flannick
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, USA
- Program in Medical and Population Genetics, Broad Institute, Cambridge, MA, USA
| | - Maddalena Trombetta
- Department of Medicine, University of Verona and Azienda Ospedaliera Universitaria Integrata of Verona, Verona, Italy
| | - Enzo Bonora
- Department of Medicine, University of Verona and Azienda Ospedaliera Universitaria Integrata of Verona, Verona, Italy
| | - Claes B Wolheim
- Lund University Diabetes Centre, Department of Clinical Sciences, Lund University, Skåne University Hospital, Malmö, Sweden
| | | | - Riccardo C Bonadonna
- Department of Medicine and Surgery, University of Parma School of Medicine and Azienda Ospedaliera Universitaria of Parma, Parma, Italy
| | - Patrik Rorsman
- Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford, UK
| | - Benjamin Davies
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | | | - Mark I McCarthy
- Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford, UK
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
- Oxford NIHR Biomedical Research Centre, Churchill Hospital, Oxford, UK
| | - Timo Otonkoski
- Stem Cells and Metabolism Research Program and Biomedicum Stem Cell Centre, Faculty of Medicine, University of Helsinki, Helsinki, Finland
| | - Jens O Lagerstedt
- Department of Experimental Medical Science, Lund University, Lund, Sweden
| | - Guy A Rutter
- Section of Cell Biology, Department of Medicine, Imperial College London, Imperial Centre for Translational and Experimental Medicine, Hammersmith, Hospital, London, UK
| | | | - Anna L Gloyn
- Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Oxford, UK
- Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
- Oxford NIHR Biomedical Research Centre, Churchill Hospital, Oxford, UK
| | - Tiinamaija Tuomi
- Institute for Molecular Medicine Finland, Helsinki University, Helsinki, Finland
- Folkhälsan Research Center, Helsinki, Finland
- Abdominal Center, Endocrinology, Helsinki University Central Hospital, Research Program for Clinical and Molecular Metabolism, University of Helsinki, Helsinki, Finland
| | - Leif Groop
- Institute for Molecular Medicine Finland, Helsinki University, Helsinki, Finland.
- Lund University Diabetes Centre, Department of Clinical Sciences, Lund University, Skåne University Hospital, Malmö, Sweden.
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Degirmenci S, Olgar Y, Durak A, Tuncay E, Turan B. Cytosolic increased labile Zn 2+ contributes to arrhythmogenic action potentials in left ventricular cardiomyocytes through protein thiol oxidation and cellular ATP depletion. J Trace Elem Med Biol 2018; 48:202-212. [PMID: 29773183 DOI: 10.1016/j.jtemb.2018.04.014] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Revised: 04/12/2018] [Accepted: 04/12/2018] [Indexed: 02/06/2023]
Abstract
Intracellular labile (free) Zn2+-level ([Zn2+]i) is low and increases markedly under pathophysiological conditions in cardiomyocytes. High [Zn2+]i is associated with alterations in excitability and ionic-conductances while exact mechanisms are not clarified yet. Therefore, we examined the elevated-[Zn2+]i on some sarcolemmal ionic-mechanisms, which can mediate cardiomyocyte dysfunction. High-[Zn2+]i induced significant changes in action potential (AP) parameters, including depolarization in resting membrane-potential and prolongations in AP-repolarizing phases. We detected also the time-dependent effects such as induction of spontaneous APs at the time of ≥ 3 min following [Zn2+]i increases, a manner of cellular ATP dependent and reversible with disulfide-reducing agent dithiothreitol, DTT. High-[Zn2+]i induced inhibitions in voltage-dependent K+-channel currents, such as transient outward K+-currents, Ito, steady-state currents, Iss and inward-rectifier K+-currents, IK1, reversible with DTT seemed to be responsible from the prolongations in APs. We, for the first time, demonstrated that lowering cellular ATP level induced significant decreaeses in both Iss and IK1, while no effect on Ito. However, the increased-[Zn2+]i could induce marked activation in ATP-sensitive K+-channel currents, IKATP, depending on low cellular ATP and thiol-oxidation levels of these channels. The mRNA levels of Kv4.3, Kv1.4 and Kv2.1 were depressed markedly with increased-[Zn2+]i with no change in mRNA level of Kv4.2, while the mRNA level of IKATP subunit, SUR2A was increased significantly with increased-[Zn2+]i, being reversible with DTT. Overall we demonstrated that high-[Zn2+]i, even if nanomolar levels, alters cardiac function via prolonged APs of cardiomyocytes, at most, due to inhibitions in voltage-dependent K+-currents, although activation of IKATP is playing cardioprotective role, through some biochemical changes in cellular ATP- and thiol-oxidation levels. It seems, a well-controlled [Zn2+]i can be novel therapeutic target for cardiac complications under pathological conditions including oxidative stress.
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Affiliation(s)
- Sinan Degirmenci
- Department of Biophysics, Faculty of Medicine, Ankara University, Ankara, Turkey
| | - Yusuf Olgar
- Department of Biophysics, Faculty of Medicine, Ankara University, Ankara, Turkey
| | - Aysegul Durak
- Department of Biophysics, Faculty of Medicine, Ankara University, Ankara, Turkey
| | - Erkan Tuncay
- Department of Biophysics, Faculty of Medicine, Ankara University, Ankara, Turkey
| | - Belma Turan
- Department of Biophysics, Faculty of Medicine, Ankara University, Ankara, Turkey.
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10
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Hershfinkel M. The Zinc Sensing Receptor, ZnR/GPR39, in Health and Disease. Int J Mol Sci 2018; 19:ijms19020439. [PMID: 29389900 PMCID: PMC5855661 DOI: 10.3390/ijms19020439] [Citation(s) in RCA: 73] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2018] [Revised: 01/24/2018] [Accepted: 01/29/2018] [Indexed: 02/07/2023] Open
Abstract
A distinct G-protein coupled receptor that senses changes in extracellular Zn2+, ZnR/GPR39, was found in cells from tissues in which Zn2+ plays a physiological role. Most prominently, ZnR/GPR39 activity was described in prostate cancer, skin keratinocytes, and colon epithelial cells, where zinc is essential for cell growth, wound closure, and barrier formation. ZnR/GPR39 activity was also described in neurons that are postsynaptic to vesicular Zn2+ release. Activation of ZnR/GPR39 triggers Gαq-dependent signaling and subsequent cellular pathways associated with cell growth and survival. Furthermore, ZnR/GPR39 was shown to regulate the activity of ion transport mechanisms that are essential for the physiological function of epithelial and neuronal cells. Thus, ZnR/GPR39 provides a unique target for therapeutically modifying the actions of zinc in a specific and selective manner.
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Affiliation(s)
- Michal Hershfinkel
- Department of Physiology and Cell Biology and The Zlotowski Center for Neuroscience, Faculty of Health Sciences, POB 653, Ben-Gurion Ave. Ben-Gurion University of the Negev, Beer Sheva 84105, Israel.
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11
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Bastos FC, Corceiro VN, Lopes SA, de Almeida JG, Matias CM, Dionisio JC, Mendes PJ, Sampaio Dos Aidos FDS, Quinta-Ferreira RM, Quinta-Ferreira ME. Effect of tolbutamide on tetraethylammonium-induced postsynaptic zinc signals at hippocampal mossy fiber-CA3 synapses. Can J Physiol Pharmacol 2017; 95:1058-1063. [PMID: 28654763 DOI: 10.1139/cjpp-2016-0379] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The application of tetraethylammonium (TEA), a blocker of voltage-dependent potassium channels, can induce long-term potentiation (LTP) in the synaptic systems CA3-CA1 and mossy fiber-CA3 pyramidal cells of the hippocampus. In the mossy fibers, the depolarization evoked by extracellular TEA induces a large amount of glutamate and also of zinc release. It is considered that zinc has a neuromodulatory role at the mossy fiber synapses, which can, at least in part, be due to the activation of presynaptic ATP-dependent potassium (KATP) channels. The aim of this work was to study properties of TEA-induced zinc signals, detected at the mossy fiber region, using the permeant form of the zinc indicator Newport Green. The application of TEA caused a depression of those signals that was partially blocked by the KATP channel inhibitor tolbutamide. After the removal of TEA, the signals usually increased to a level above baseline. These results are in agreement with the idea that intense zinc release during strong synaptic events triggers a negative feedback action. The zinc depression, caused by the LTP-evoking chemical stimulation, turns into potentiation after TEA washout, suggesting the existence of a correspondence between the observed zinc potentiation and TEA-evoked mossy fiber LTP.
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Affiliation(s)
- Fatima C Bastos
- a Department of Physics, University of Coimbra, P-3004-516 Coimbra, Portugal
| | - Vanessa N Corceiro
- a Department of Physics, University of Coimbra, P-3004-516 Coimbra, Portugal
| | - Sandra A Lopes
- a Department of Physics, University of Coimbra, P-3004-516 Coimbra, Portugal
| | - José G de Almeida
- b Department of Life Sciences, University of Coimbra, P-3000-456 Coimbra, Portugal
| | - Carlos M Matias
- c CNC - Center for Neurosciences and Cell Biology, University of Coimbra, P-3004-504 Coimbra, Portugal.,d UTAD - University of Trás-os-montes and Alto Douro, P-5000-801 Vila Real, Portugal
| | - Jose C Dionisio
- c CNC - Center for Neurosciences and Cell Biology, University of Coimbra, P-3004-504 Coimbra, Portugal.,e Departamento de Biologia Animal, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
| | - Paulo J Mendes
- a Department of Physics, University of Coimbra, P-3004-516 Coimbra, Portugal.,f LIP - Laboratory of Instrumentation and Experimental Particles Physics, P-3004-516 Coimbra, Portugal
| | | | - Rosa M Quinta-Ferreira
- h CIEPQPF - Research Centre of Chemical Process Engineering and Forest Products, Department of Chemical Engineering, University of Coimbra, P-3030-790 Coimbra, Portugal
| | - M Emilia Quinta-Ferreira
- a Department of Physics, University of Coimbra, P-3004-516 Coimbra, Portugal.,c CNC - Center for Neurosciences and Cell Biology, University of Coimbra, P-3004-504 Coimbra, Portugal
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12
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Yabuki Y, Jing X, Fukunaga K. The T-type calcium channel enhancer SAK3 inhibits neuronal death following transient brain ischemia via nicotinic acetylcholine receptor stimulation. Neurochem Int 2017; 108:272-281. [PMID: 28457878 DOI: 10.1016/j.neuint.2017.04.015] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2017] [Revised: 04/26/2017] [Accepted: 04/26/2017] [Indexed: 02/06/2023]
Abstract
The T-type calcium channel enhancer SAK3 (ethyl 8'-methyl-2',4-dioxo-2-(piperidin-1-yl)-2'H-spiro[cyclopentane-1,3'-imidazo[1,2-a]pyridin]-2-ene-3-carboxylate) promotes acetylcholine (ACh) release in mouse hippocampus, enhancing cognitive function. Here, we tested SAK3 neuroprotective activity in the context of transient brain ischemia using a 20-min bilateral common carotid arteries occlusion (BCCAO) mouse model. Mice were administered with SAK3 (0.1, 0.5 or 1.0 mg/kg, p.o.) 24 h after BCCAO ischemia. Oral SAK3 (0.5 or 1.0 mg/kg/day, p.o.) administration significantly blocked loss of hippocampal CA1 neurons and memory deficits seen in BCCAO mice. Treatment with α7 nicotinic ACh receptor (nAChR)-selective inhibitor methyllycaconitine (MLA: 6.0 mg/kg/day, i.p.) significantly antagonized both neuroprotection and improvement in memory promoted by SAK3 (0.5 mg/kg/day, p.o.). Acute SAK3 (0.5 mg/kg, p.o.) administration significantly enhanced protein kinase B (Akt) phosphorylation levels in CA1 of control and BCCAO mice. Importantly, treatment of control and BCCAO mice with the non-selective nAChR antagonist mecamylamine (MEC: 1.0 mg/kg, i.p.) or the α7-selective nAChR antagonist MLA (6.0 mg/kg, i.p.), but not the M1 muscarinic ACh receptor (mAChR) antagonist pirenzepine (PZ: 10 mg/kg, i.p.), blocked enhanced Akt activity elicited by SAK3 (0.5 mg/kg, p.o.). We also confirmed that decreased phosphorylated Akt immunoreactivities were rescued by SAK3 (0.5 mg/kg, p.o.) administration in NeuN-positive CA1 neurons of BCCAO mice, an effect blocked by MLA (6.0 mg/kg, i.p.). Finally, we observed α7 nAChR and phosphorylated Akt expression in CA1 pyramidal neurons. We conclude that the T-type calcium channel enhancer SAK3 is neuroprotective in the context of brain ischemia by stimulating nicotinic cholinergic neurotransmission.
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Affiliation(s)
- Yasushi Yabuki
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan
| | - Xu Jing
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan
| | - Kohji Fukunaga
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan.
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13
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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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14
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Chabosseau P, Rutter GA. Zinc and diabetes. Arch Biochem Biophys 2016; 611:79-85. [DOI: 10.1016/j.abb.2016.05.022] [Citation(s) in RCA: 105] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Revised: 05/09/2016] [Accepted: 05/31/2016] [Indexed: 01/09/2023]
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15
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Quinta-Ferreira ME, Sampaio Dos Aidos FDS, Matias CM, Mendes PJ, Dionísio JC, Santos RM, Rosário LM, Quinta-Ferreira RM. Modelling zinc changes at the hippocampal mossy fiber synaptic cleft. J Comput Neurosci 2016; 41:323-337. [PMID: 27696002 DOI: 10.1007/s10827-016-0620-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Revised: 08/11/2016] [Accepted: 08/15/2016] [Indexed: 01/18/2023]
Abstract
Zinc, a transition metal existing in very high concentrations in the hippocampal mossy fibers from CA3 area, is assumed to be co-released with glutamate and to have a neuromodulatory role at the corresponding synapses. The synaptic action of zinc is determined both by the spatiotemporal characteristics of the zinc release process and by the kinetics of zinc binding to sites located in the cleft area, as well as by their concentrations. This work addresses total, free and complexed zinc concentration changes, in an individual synaptic cleft, following single, short and long periods of evoked zinc release. The results estimate the magnitude and time course of the concentrations of zinc complexes, assuming that the dynamics of the release processes are similar to those of glutamate. It is also considered that, for the cleft zinc concentrations used in the model (≤ 1 μM), there is no postsynaptic zinc entry. For this reason, all released zinc ends up being reuptaken in a process that is several orders of magnitude slower than that of release and has thus a much smaller amplitude. The time derivative of the total zinc concentration in the cleft is represented by the difference between two alpha functions, corresponding to the released and uptaken components. These include specific parameters that were chosen assuming zinc and glutamate co-release, with similar time courses. The peak amplitudes of free zinc in the cleft were selected based on previously reported experimental cleft zinc concentration changes evoked by single and multiple stimulation protocols. The results suggest that following a low amount of zinc release, similar to that associated with one or a few stimuli, zinc clearance is mainly mediated by zinc binding to the high-affinity sites on the NMDA receptors and to the low-affinity sites on the highly abundant GLAST glutamate transporters. In the case of higher zinc release brought about by a larger group of stimuli, most zinc binding occurs essentially to the GLAST transporters, having the corresponding zinc complex a maximum concentration that is more than one order of magnitude larger than that for the high and low affinity NMDA sites. The other zinc complexes considered in the model, namely those formed with sites on the AMPA receptors, calcium and KATP channels and with ATP molecules, have much smaller contributions to the synaptic zinc clearance.
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Affiliation(s)
- M E Quinta-Ferreira
- CNC- Center for Neuroscience and Cell Biology, University of Coimbra, P-3004-504, Coimbra, Portugal.
- Department of Physics, University of Coimbra, P-3004-516, Coimbra, Portugal.
| | - F D S Sampaio Dos Aidos
- CNC- Center for Neuroscience and Cell Biology, University of Coimbra, P-3004-504, Coimbra, Portugal
- Department of Physics, University of Coimbra, P-3004-516, Coimbra, Portugal
- CFisUC, Department of Physics, University of Coimbra, P-3004-516, Coimbra, Portugal
| | - C M Matias
- CNC- Center for Neuroscience and Cell Biology, University of Coimbra, P-3004-504, Coimbra, Portugal
- UTAD- University of Trás-os-montes and Alto Douro, P-5000-801, Vila Real, Portugal
| | - P J Mendes
- Department of Physics, University of Coimbra, P-3004-516, Coimbra, Portugal
- LIP- Laboratory of Instrumentation and Experimental Particles Physics, P-3004-516, Coimbra, Portugal
| | - J C Dionísio
- CNC- Center for Neuroscience and Cell Biology, University of Coimbra, P-3004-504, Coimbra, Portugal
- Department of Animal Biology, University of Lisbon, P-1749-016, Lisbon, Portugal
| | - R M Santos
- CNC- Center for Neuroscience and Cell Biology, University of Coimbra, P-3004-504, Coimbra, Portugal
- Department of Life Sciences, University of Coimbra, P-3004-516, Coimbra, Portugal
| | - L M Rosário
- CNC- Center for Neuroscience and Cell Biology, University of Coimbra, P-3004-504, Coimbra, Portugal
- Department of Life Sciences, University of Coimbra, P-3004-516, Coimbra, Portugal
| | - R M Quinta-Ferreira
- CIEPQPF - Research Centre of Chemical Process Engineering and Forest Products, Department of Chemical Engineering, University of Coimbra, P-3030-790, Coimbra, Portugal
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16
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Peralta FA, Huidobro-Toro JP. Zinc as Allosteric Ion Channel Modulator: Ionotropic Receptors as Metalloproteins. Int J Mol Sci 2016; 17:E1059. [PMID: 27384555 PMCID: PMC4964435 DOI: 10.3390/ijms17071059] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Revised: 06/20/2016] [Accepted: 06/22/2016] [Indexed: 12/20/2022] Open
Abstract
Zinc is an essential metal to life. This transition metal is a structural component of many proteins and is actively involved in the catalytic activity of cell enzymes. In either case, these zinc-containing proteins are metalloproteins. However, the amino acid residues that serve as ligands for metal coordination are not necessarily the same in structural proteins compared to enzymes. While crystals of structural proteins that bind zinc reveal a higher preference for cysteine sulfhydryls rather than histidine imidazole rings, catalytic enzymes reveal the opposite, i.e., a greater preference for the histidines over cysteines for catalysis, plus the influence of carboxylic acids. Based on this paradigm, we reviewed the putative ligands of zinc in ionotropic receptors, where zinc has been described as an allosteric modulator of channel receptors. Although these receptors do not strictly qualify as metalloproteins since they do not normally bind zinc in structural domains, they do transitorily bind zinc at allosteric sites, modifying transiently the receptor channel's ion permeability. The present contribution summarizes current information showing that zinc allosteric modulation of receptor channels occurs by the preferential metal coordination to imidazole rings as well as to the sulfhydryl groups of cysteine in addition to the carboxyl group of acid residues, as with enzymes and catalysis. It is remarkable that most channels, either voltage-sensitive or transmitter-gated receptor channels, are susceptible to zinc modulation either as positive or negative regulators.
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Affiliation(s)
- Francisco Andrés Peralta
- Laboratorio de Farmacología de Nucleótidos, Laboratorio de Farmacología, Departamento de Biología, Facultad de Química y Biología, y Centro para el Desarrollo de Nanociencias y Nanotecnología (CEDENNA), Universidad de Santiago de Chile, Alameda Libertador B. O'Higgins, 3363 Santiago, Chile.
| | - Juan Pablo Huidobro-Toro
- Laboratorio de Farmacología de Nucleótidos, Laboratorio de Farmacología, Departamento de Biología, Facultad de Química y Biología, y Centro para el Desarrollo de Nanociencias y Nanotecnología (CEDENNA), Universidad de Santiago de Chile, Alameda Libertador B. O'Higgins, 3363 Santiago, Chile.
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17
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Moran BM, Abdel-Wahab YHA, Vasu S, Flatt PR, McKillop AM. GPR39 receptors and actions of trace metals on pancreatic beta cell function and glucose homoeostasis. Acta Diabetol 2016; 53:279-93. [PMID: 26112416 DOI: 10.1007/s00592-015-0781-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/21/2015] [Accepted: 05/29/2015] [Indexed: 10/23/2022]
Abstract
AIMS G-protein-coupled receptor 39 (GPR39) has been implicated in glucose homoeostasis, appetite control and gastrointestinal tract function. METHODS This study used clonal BRIN-BD11 cells and mouse pancreatic islets to assess the insulin-releasing actions of trace metals believed to act via GPR39, and the second messenger pathways involved in mediating their effects. Micromolar concentrations of Zn(2+), Cu(2+), Ni(2+) and Co(2+) were examined under normoglycaemic and hyperglycaemic conditions. Mechanistic studies investigated changes of intracellular Ca(2+), cAMP generation and assessment of cytotoxicity by LDH release. Cellular localisation of GPR39 was determined by double immunohistochemical staining. RESULTS All trace metals (7.8-500 µmol/l) stimulated insulin release with Cu(2+) being the most potent in isolated islets, with an EC50 value of 87 μmol/l. Zn(2+) was the most selective with an EC50 value of 125 μmol/l. Enhancement of insulin secretion was also observed with Ni(2+) (179 μmol/l) and Co(2+) (190 μmol/l). These insulin-releasing effects were confirmed using clonal BRIN-BD11 cells which exhibited enhanced intracellular Ca(2+) (p < 0.05-p < 0.001) and cAMP generation (p < 0.05-p < 0.001) in response to trace metals. Oral administration of Zn(2+), Ni(2+) and Cu(2+) (50 µmol/kg together with 18 mmol/kg glucose) decreased the glycaemic excursion (p < 0.05-p < 0.01) and augmented insulin secretion (p < 0.05-p < 0.01) in NIH Swiss mice. CONCLUSIONS This study has demonstrated the presence of GPR39 and the insulinotropic actions of trace metals on BRIN-BD11 cells and pancreatic beta cells, together with their antihyperglycaemic actions in vivo. These data suggest that development of agonists capable of specifically activating GPR39 may be a useful new therapeutic approach for diabetes management.
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Affiliation(s)
- Brian M Moran
- Biomedical Sciences Research Institute, SAAD Centre for Pharmacy and Diabetes, University of Ulster, Cromore Road, Coleraine, BT52 1SA, Northern Ireland, UK
| | - Yasser H A Abdel-Wahab
- Biomedical Sciences Research Institute, SAAD Centre for Pharmacy and Diabetes, University of Ulster, Cromore Road, Coleraine, BT52 1SA, Northern Ireland, UK
| | - Srividya Vasu
- Biomedical Sciences Research Institute, SAAD Centre for Pharmacy and Diabetes, University of Ulster, Cromore Road, Coleraine, BT52 1SA, Northern Ireland, UK
| | - Peter R Flatt
- Biomedical Sciences Research Institute, SAAD Centre for Pharmacy and Diabetes, University of Ulster, Cromore Road, Coleraine, BT52 1SA, Northern Ireland, UK
| | - Aine M McKillop
- Biomedical Sciences Research Institute, SAAD Centre for Pharmacy and Diabetes, University of Ulster, Cromore Road, Coleraine, BT52 1SA, Northern Ireland, UK.
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18
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Hutchens T, Piston DW. EphA4 Receptor Forward Signaling Inhibits Glucagon Secretion From α-Cells. Diabetes 2015; 64:3839-51. [PMID: 26251403 PMCID: PMC4613968 DOI: 10.2337/db15-0488] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Accepted: 07/29/2015] [Indexed: 12/18/2022]
Abstract
The loss of inhibition of glucagon secretion exacerbates hyperglycemia in type 1 and 2 diabetes. However, the molecular mechanisms that regulate glucagon secretion in unaffected and diabetic states remain relatively unexplained. We present evidence supporting a new model of juxtacrine-mediated regulation of glucagon secretion where neighboring islet cells negatively regulate glucagon secretion through tonic stimulation of α-cell EphA receptors. Primarily through EphA4 receptors, this stimulation correlates with maintenance of a dense F-actin network. In islets, additional stimulation and inhibition of endogenous EphA forward signaling result in inhibition and enhancement, respectively, of glucagon secretion, accompanied by an increase and decrease, respectively, in α-cell F-actin density. Sorted α-cells lack endogenous stimulation of EphA forward signaling from neighboring cells, resulting in enhanced basal glucagon secretion as compared with islets and the elimination of glucose inhibition of glucagon secretion. Restoration of EphA forward signaling in sorted α-cells recapitulates both normal basal glucagon secretion and glucose inhibition of glucagon secretion. Additionally, α-cell-specific EphA4(-/-) mice exhibit abnormal glucagon dynamics, and EphA4(-/-) α-cells contain less dense F-actin networks than EphA4(+/+) α-cells. This juxtacrine-mediated model provides insight into the functional and dysfunctional regulation of glucagon secretion and opens up new therapeutic strategies for the clinical management of diabetes.
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Affiliation(s)
- Troy Hutchens
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
| | - David W Piston
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO
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19
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Slepchenko KG, Daniels NA, Guo A, Li YV. Autocrine effect of Zn²⁺ on the glucose-stimulated insulin secretion. Endocrine 2015; 50:110-22. [PMID: 25771886 DOI: 10.1007/s12020-015-0568-z] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Accepted: 03/02/2015] [Indexed: 12/30/2022]
Abstract
It is well known that zinc (Zn(2+)) is required for the process of insulin biosynthesis and the maturation of insulin secretory granules in pancreatic beta (β)-cells, and that changes in Zn(2+) levels in the pancreas have been found to be associated with diabetes. Glucose-stimulation causes a rapid co-secretion of Zn(2+) and insulin with similar kinetics. However, we do not know whether Zn(2+) regulates insulin availability and secretion. Here we investigated the effect of Zn(2+) on glucose-stimulated insulin secretion (GSIS) in isolated mouse pancreatic islets. Whereas Zn(2+) alone (control) had no effect on the basal secretion of insulin, it significantly inhibited GSIS. The application of CaEDTA, by removing the secreted Zn(2+) from the extracellular milieu of the islets, resulted in significantly increased GSIS, suggesting an overall inhibitory role of secreted Zn(2+) on GSIS. The inhibitory action of Zn(2+) was mostly mediated through the activities of KATP/Ca(2+) channels. Furthermore, during brief paired-pulse glucose-stimulated Zn(2+) secretion (GSZS), Zn(2+) secretion following the second pulse was significantly attenuated, probably by the secreted endogenous Zn(2+) after the first pulse. Such an inhibition on Zn(2+) secretion following the second pulse was completely reversed by Zn(2+) chelation, suggesting a negative feedback mechanism, in which the initial glucose-stimulated Zn(2+) release inhibits subsequent Zn(2+) secretion, subsequently inhibiting insulin co-secretion as well. Taken together, these data suggest a negative feedback mechanism on GSZS and GSIS by Zn(2+) secreted from β-cells, and the co-secreted Zn(2+) may act as an autocrine inhibitory modulator.
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Affiliation(s)
- Kira G Slepchenko
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH, 45701, USA
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20
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Beltrán C, Rodríguez-Miranda E, Granados-González G, de De la Torre LG, Nishigaki T, Darszon A. Zn(2+) induces hyperpolarization by activation of a K(+) channel and increases intracellular Ca(2+) and pH in sea urchin spermatozoa. Dev Biol 2014; 394:15-23. [PMID: 25092071 PMCID: PMC4163537 DOI: 10.1016/j.ydbio.2014.07.017] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Revised: 07/01/2014] [Accepted: 07/24/2014] [Indexed: 11/24/2022]
Abstract
Zinc (Zn(2+)) has been recently recognized as a crucial element for male gamete function in many species although its detailed mechanism of action is poorly understood. In sea urchin spermatozoa, Zn(2+) was reported as an essential trace ion for efficient sperm motility initiation and the acrosome reaction by modulating intracellular pH (pHi). In this study we found that submicromolar concentrations of free Zn(2+) change membrane potential (Em) and increase the concentration of intracellular Ca(2+) ([Ca(2+)]i) and cAMP in Lytechinus pictus sperm. Our results indicate that the Zn(2+) response in sperm of this species mainly involves an Em hyperpolarization caused by K(+) channel activation. The pharmacological profile of the Zn(2+)-induced hyperpolarization indicates that the cGMP-gated K(+) selective channel (tetraKCNG/CNGK), which is crucial for speract signaling, is likely a main target for Zn(2+). Considering that Zn(2+) also induces [Ca(2+)]i fluctuations, our observations suggest that Zn(2+) activates the signaling cascade of speract, except for an increase in cGMP, and facilitates sperm motility initiation upon spawning. These findings provide new insights about the role of Zn(2+) in male gamete function.
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Affiliation(s)
- Carmen Beltrán
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos CP 62210, México
| | - Esmeralda Rodríguez-Miranda
- Departamento de Medicina y Nutrición, División de Ciencias de la Salud, Universidad de Guanajuato; Campus León. Guanajuato CP 37320, México
| | - Gisela Granados-González
- Facultad de Ciencias, Universidad Autónoma del Estado de México, Toluca, Estado de México CP 50000, México
| | | | - Takuya Nishigaki
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos CP 62210, México
| | - Alberto Darszon
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos CP 62210, México
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21
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Abstract
Zinc (Zn2+) is an essential element crucial for growth and development, and also plays a role in cell signaling for cellular processes like cell division and apoptosis. In the mammalian pancreas, Zn2+ is essential for the correct processing, storage, secretion, and action of insulin in beta (β)-cells. Insulin is stored inside secretory vesicles or granules, where two Zn2+ ions coordinate six insulin monomers to form the hexameric-structure on which maturated insulin crystals are based. The total Zn2+ content of the mammalian pancreas is among the highest in the body, and Zn2+ concentration reach millimolar levels in the interior of the dense-core granule. Changes in Zn2+ levels in the pancreas have been found to be associated with diabetes. Hence, the relationship between co-stored Zn2+ and insulin undoubtedly is critical to normal β-cell function. The advances in the field of Zn2+ biology over the last decade have facilitated our understanding of Zn2+ trafficking, its intracellular distribution and its storage. When exocytosis of insulin occurs, insulin granules fuse with the β-cell plasma membrane and release their contents, i.e., insulin as well as substantial amount of free Zn2+, into the extracellular space and the local circulation. Studies increasingly indicate that secreted Zn2+ has autocrine or paracrine signaling in β-cells or the neighboring cells. This review discusses the Zn2+ homeostasis in β-cells with emphasis on the potential signaling role of Zn2+ to islet biology.
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Affiliation(s)
- Yang V Li
- Department of Biomedical Sciences, Ohio University Heritage College of Osteopathic Medicine, 346 Irvine Hall, Athens, OH, 45701, USA,
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22
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Slepchenko KG, James CBL, Li YV. Inhibitory effect of zinc on glucose-stimulated zinc/insulin secretion in an insulin-secreting β-cell line. Exp Physiol 2013; 98:1301-11. [PMID: 23603373 DOI: 10.1113/expphysiol.2013.072348] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Diminished or inappropriate secretion of insulin is associated with type II diabetes. The cellular/molecular mechanism coupled with the regulation of insulin secretion is still under intense investigation. Divalent ion zinc (Zn(2+)) is co-packaged and co-secreted with insulin and is intimately involved in the process of insulin biosynthesis and the maturation of insulin secretory granules. The study reported here investigated glucose-stimulated zinc secretion (GSZS) and the effect of zinc on glucose-stimulated insulin secretion (GSIS) in the HIT-T15 pancreatic β-cell line. Zinc secretion was measured using a newly developed fluorescent zinc imaging approach, and the insulin secretion was measured using an enzyme-linked immunosorbent assay. There was apparent granular-like zinc staining in β-cells. The application of glucose induced detectable zinc secretion or GSZS. Like GSIS, GSZS was dependent on the glucose concentration (5-20 mm) and the presence of extracellular calcium. The application of a zinc chelator enhanced GSZS. When brief paired-pulse glucose stimulations, which involve the initial glucose stimulation followed by a second round of glucose stimulation, were applied, zinc secretion or GSZS that followed the first pulse was inhibited. This inhibition was reversed by zinc chelation, suggesting a feedback mechanism on GSZS by zinc secreted from β-cells. Finally, the application of zinc (50 μm) strongly inhibited GSIS as measured by enzyme-linked immunosorbent assay. The present study suggests that insulin secretion is regulated by co-secreted zinc that may act as an autocrine inhibitory modulator.
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Affiliation(s)
- Kira G Slepchenko
- Department of Biomedical Sciences, Ohio University Heritage College of Osteopathic Medicine, Athens, OH 45701, USA
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23
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Loder MK, Tsuboi T, Rutter GA. Live-cell imaging of vesicle trafficking and divalent metal ions by total internal reflection fluorescence (TIRF) microscopy. Methods Mol Biol 2013; 950:13-26. [PMID: 23086867 DOI: 10.1007/978-1-62703-137-0_2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Total internal reflection fluorescence (TIRF) microscopy is an especially powerful tool for visualizing live cellular events. Fluorescent molecules alone provide broad information about the expression and localization of proteins and other molecules; however, the temporal and spatial resolution is confounded by signal from outside the area of interest and the intensity of the illumination required. TIRF overcomes this limitation by using the reflective properties of a laser beam to illuminate a narrow (<100 nm) strip at the surface of a cell with a relatively low powered evanescent wave, thus making it possible to measure events occurring specifically at the plasma membrane such as exocytosis, single molecule interactions, and ionic changes during signal transduction. Here we describe some of the methods for using TIRF microscopy to study the processes involved in exocytosis from excitable cells (i.e., neurons, endocrine, neuroendocrine, and exocrine cells) and the release of physiologically active substances (i.e., neurotransmitters, hormones, and mucus).The failure of regulated exocytosis is associated with various diseases such as allergy, brain dysfunction, and endocrine illness. Diabetes mellitus, which is due to an absolute (type I) or relative (type II) deficiency of insulin secretion from pancreatic β-cells, is a major area of therapeutic interest. Insulin is stored in dense core vesicles with Zn(2+) ions in pancreatic β-cells. Insulin secretion is regulated by plasma glucose concentration which acts through intracellular metabolism to influence intracellular [Ca(2+)]. However, the precise molecular mechanisms controlling insulin granule movement towards, and fusion at, the plasma membrane remain only partially understood. To tackle this problem, we have used live cell imaging techniques to image regulated exocytosis in single living β-cells alongside intracellular Ca(2+) and Zn(2+) concentrations.
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Affiliation(s)
- Merewyn K Loder
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Faculty of Medicine, Imperial College London, London, UK
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Robertson RP, Zhou H, Slucca M. A role for zinc in pancreatic islet β-cell cross-talk with the α-cell during hypoglycaemia. Diabetes Obes Metab 2011; 13 Suppl 1:106-11. [PMID: 21824263 DOI: 10.1111/j.1463-1326.2011.01448.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Signalling by intraislet β-cells to neighbouring α-cells was recognized almost 40 years ago, leading to the hypothesis that this is an essential mechanism to regulate the glucagon counterregulatory response to hypoglycaemia. The thesis was that during normoglycaemia or hyperglycaemia insulin secretion from β-cells would enter the islet periportal circulation and travel downstream to α-cells to dampen glucagon secretion. As a corollary, during hypoglycaemia β-cells would stop secreting insulin, which would permit α-cells to release glucagon into the hepatic portal circulation so it could travel to the liver to increase glucose production and thereby correct hypoglycaemia. This mini-review briefly mentions the early work that established this hypothesis and more extensively examines more recent work that has provided direct evidence supporting the hypothesis. A new twist has been introduced based on the fact that zinc is bound to insulin within β-cells and co-secreted with insulin. Zinc is released from insulin when it reaches the higher pH of blood, and zinc has recently been shown to negatively regulate α-cell secretion. It is now suggested that a switch-off signal provided by a sudden cessation of zinc secretion from β-cells during hypoglycaemia may play a critical role in stimulating glucagon secretion that is independent of the effect of insulin.
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Affiliation(s)
- R P Robertson
- Pacific Northwest Diabetes Research Institute and Division of Endocrinology and Metabolism, Department of Medicine and Pharmacology, University of Washington, Seattle, WA 98122, USA.
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25
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Hardy AB, Serino AS, Wijesekara N, Chimienti F, Wheeler MB. Regulation of glucagon secretion by zinc: lessons from the β cell-specific Znt8 knockout mouse model. Diabetes Obes Metab 2011; 13 Suppl 1:112-7. [PMID: 21824264 DOI: 10.1111/j.1463-1326.2011.01451.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In type-2 diabetes, hyperglucagonaemia aggravates elevated blood glucose levels. Relative to our knowledge of the β-cell and insulin secretion, there remains a limited understanding of glucagon secretion in α-cells. Regulation of glucagon may be dependent on a combination of factors, which include direct glucose sensing by the α-cell, innervations from the autonomic nervous system and potential 'paracrine' actions by hormones and factors that are released by adjacent endocrine cells within the islets. The list of potential 'paracrine' regulators within the islet includes insulin, somatostatin, γ-aminobutyric acid, glutamate and zinc. Zinc crystallises with insulin in β-cells and is co-secreted with insulin. In the scientific literature, the effect of exogeneous zinc on glucagon secretion has been debated. Here, we confirm that an increase in exogeneous zinc does inhibit glucagon secretion. To determine if there are physiological effects of zinc on glucagon secretion we used a β-cell-specific ZnT8 knockout (Znt8BKO) mouse model. Znt8BKO mice, despite showing lower granular zinc content in β-cells, showed no changes in fasted plasma glucagon levels and glucose regulated glucagon secretion. These findings suggest that zinc secreted from β-cell does not regulate glucagon secretion.
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Affiliation(s)
- A B Hardy
- Department of Physiology, University of Toronto, 1 King's College Circle, Toronto, ON, Canada
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26
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Yang W, Manna PT, Zou J, Luo J, Beech DJ, Sivaprasadarao A, Jiang LH. Zinc inactivates melastatin transient receptor potential 2 channels via the outer pore. J Biol Chem 2011; 286:23789-98. [PMID: 21602277 PMCID: PMC3129160 DOI: 10.1074/jbc.m111.247478] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2011] [Revised: 05/19/2011] [Indexed: 10/18/2022] Open
Abstract
Zinc ion (Zn(2+)) is an endogenous allosteric modulator that regulates the activity of a wide variety of ion channels in a reversible and concentration-dependent fashion. Here we used patch clamp recording to study the effects of Zn(2+) on the melastatin transient receptor potential 2 (TRPM2) channel. Zn(2+) inhibited the human (h) TRPM2 channel currents, and the steady-state inhibition was largely not reversed upon washout and concentration-independent in the range of 30-1000 μM, suggesting that Zn(2+) induces channel inactivation. Zn(2+) inactivated the channels fully when they conducted inward currents, but only by half when they passed outward currents, indicating profound influence of the permeant ion on Zn(2+) inactivation. Alanine substitution scanning mutagenesis of 20 Zn(2+)-interacting candidate residues in the outer pore region of the hTRPM2 channel showed that mutation of Lys(952) in the extracellular end of the fifth transmembrane segment and Asp(1002) in the large turret strongly attenuated or abolished Zn(2+) inactivation, and mutation of several other residues dramatically changed the inactivation kinetics. The mouse (m) TRPM2 channels were also inactivated by Zn(2+), but the kinetics were remarkably slower. Reciprocal mutation of His(995) in the hTRPM2 channel and the equivalent Gln(992) in the mTRPM2 channel completely swapped the kinetics, but no such opposing effects resulted from exchanging another pair of species-specific residues, Arg(961)/Ser(958). We conclude from these results that Zn(2+) inactivates the TRPM2 channels and that residues in the outer pore are critical determinants of the inactivation.
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Affiliation(s)
- Wei Yang
- From the Institute of Membrane and Systems Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom and
- the Department of Neurobiology, Zhejiang University School of Medicine, Zhejiang 310058, China
| | - Paul T. Manna
- From the Institute of Membrane and Systems Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom and
| | - Jie Zou
- From the Institute of Membrane and Systems Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom and
| | - Jianhong Luo
- the Department of Neurobiology, Zhejiang University School of Medicine, Zhejiang 310058, China
| | - David J. Beech
- From the Institute of Membrane and Systems Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom and
| | - Asipu Sivaprasadarao
- From the Institute of Membrane and Systems Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom and
| | - Lin-Hua Jiang
- From the Institute of Membrane and Systems Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom and
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27
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Matias C, Saggau P, Quinta-Ferreira M. Blockade of presynaptic K ATP channels reduces the zinc-mediated posttetanic depression at hippocampal mossy fiber synapses. Brain Res 2010; 1320:22-7. [DOI: 10.1016/j.brainres.2010.01.021] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2009] [Revised: 01/07/2010] [Accepted: 01/10/2010] [Indexed: 10/19/2022]
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Slucca M, Harmon JS, Oseid EA, Bryan J, Robertson RP. ATP-sensitive K+ channel mediates the zinc switch-off signal for glucagon response during glucose deprivation. Diabetes 2010; 59:128-34. [PMID: 19808893 PMCID: PMC2797913 DOI: 10.2337/db09-1098] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE The intraislet insulin hypothesis proposes that glucagon secretion during hypoglycemia is triggered by a decrease in intraislet insulin secretion. A more recent hypothesis based on in vivo data from hypoglycemic rats is that it is the decrease in zinc cosecreted with insulin from beta-cells, rather than the decrease in insulin itself, that signals glucagon secretion from alpha-cells during hypoglycemia. These studies were designed to determine whether closure of the alpha-cell ATP-sensitive K(+) channel (K(ATP) channel) is the mechanism through which the zinc switch-off signal triggers glucagon secretion during glucose deprivation. RESEARCH DESIGN AND METHODS All studies were performed using perifused isolated islets. RESULTS In control experiments, the expected glucagon response to an endogenous insulin switch-off signal during glucose deprivation was observed in wild-type mouse islets. In experiments with streptozotocin-treated wild-type islets, a glucagon response to an exogenous zinc switch-off signal was observed during glucose deprivation. However, this glucagon response to the zinc switch-off signal during glucose deprivation was not seen in the presence of nifedipine, diazoxide, or tolbutamide or if K(ATP) channel knockout mouse islets were used. All islets had intact glucagon responses to epinephrine. CONCLUSIONS These data demonstrate that closure of K(ATP) channels and consequent opening of calcium channels is the mechanism through which the zinc switch-off signal triggers glucagon secretion during glucose deprivation.
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Affiliation(s)
- Michela Slucca
- From the Pacific Northwest Diabetes Research Institute and the Division of Metabolism, Endocrinology, and Nutrition, Department of Medicine and Department of Pharmacology, University of Washington, Seattle, Washington
| | - Jamie S. Harmon
- From the Pacific Northwest Diabetes Research Institute and the Division of Metabolism, Endocrinology, and Nutrition, Department of Medicine and Department of Pharmacology, University of Washington, Seattle, Washington
| | - Elizabeth A. Oseid
- From the Pacific Northwest Diabetes Research Institute and the Division of Metabolism, Endocrinology, and Nutrition, Department of Medicine and Department of Pharmacology, University of Washington, Seattle, Washington
| | - Joseph Bryan
- From the Pacific Northwest Diabetes Research Institute and the Division of Metabolism, Endocrinology, and Nutrition, Department of Medicine and Department of Pharmacology, University of Washington, Seattle, Washington
| | - R. Paul Robertson
- From the Pacific Northwest Diabetes Research Institute and the Division of Metabolism, Endocrinology, and Nutrition, Department of Medicine and Department of Pharmacology, University of Washington, Seattle, Washington
- Corresponding author: R. Paul Robertson,
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29
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Abstract
It is well known that zinc is required in pancreatic beta-cells in the process of insulin biosynthesis and the maturation of insulin secretory granules. In fact, the zinc level in pancreatic islets is amongst the highest in the body and reduction in its levels in the pancreas has been associated with diabetes. High concentrations of zinc can also be toxic because of enhanced oxidative damage. The link between zinc, diabetes and islet dysfunction has recently been reiterated by genomewide association studies that identified an islet cell membrane zinc transporter, SLC30A8 (ZnT8), as one of the risk loci for type 2 diabetes. Here we explore the importance of both zinc and ZnT8 to islet biology and whole body glucose homeostasis.
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Affiliation(s)
- N Wijesekara
- Department of Physiology, University of Toronto, Ontario, Canada
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30
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Matias CM, Sousa JM, Quinta-Ferreira ME, Arif M, Burrows HD. Validation of TPEN as a zinc chelator in fluorescence probing of calcium in cells with the indicator Fura-2. J Fluoresc 2009; 20:377-80. [PMID: 19821015 DOI: 10.1007/s10895-009-0539-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2009] [Accepted: 09/14/2009] [Indexed: 11/29/2022]
Abstract
Fura-2 is widely used as a fluorescent probe to monitor dynamic changes in cytosolic free calcium in cells, where Ca(2+) can enter through several types of voltage-operated or ligand-gated channels. However, Fura-2 is also sensitive to other metal ions, such as zinc, which may be involved in ionic channels and receptors. There is interest, in particular, in studying the synapses between mossy fibers and CA3 pyramidal cells which contain both calcium and high quantities of free or loosely bound zinc. We have found, through fluorescence probing, that endogenous zinc inhibits mossy fiber calcium transients. However, since these results might be explained by an effect of the zinc chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) on the spectral properties of Fura-2, we have carried out a validation of the method through fluorescence excitation spectra of the complex Fura-2/calcium, and show that TPEN does not affect these spectra. This supports the idea that the observed calcium enhancement is related to a zinc inhibition of presynaptic calcium mechanisms, and confirms the use of the chelator TPEN as a general procedure for the biophysical study of Ca(II) in the presence of Zn(II) using Fura-2.
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Affiliation(s)
- Carlos M Matias
- Department of Physics, University of Trás-os-Montes and Alto Douro (UTAD), 5000-911, Vila Real, Portugal.
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31
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Insulin crystallization depends on zinc transporter ZnT8 expression, but is not required for normal glucose homeostasis in mice. Proc Natl Acad Sci U S A 2009; 106:14872-7. [PMID: 19706465 DOI: 10.1073/pnas.0906587106] [Citation(s) in RCA: 241] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Zinc co-crystallizes with insulin in dense core secretory granules, but its role in insulin biosynthesis, storage and secretion is unknown. In this study we assessed the role of the zinc transporter ZnT8 using ZnT8-knockout (ZnT8(-/-)) mice. Absence of ZnT8 expression caused loss of zinc release upon stimulation of exocytosis, but normal rates of insulin biosynthesis, normal insulin content and preserved glucose-induced insulin release. Ultrastructurally, mature dense core insulin granules were rare in ZnT8(-/-) beta cells and were replaced by immature, pale insulin "progranules," which were larger than in ZnT8(+/+) islets. When mice were fed a control diet, glucose tolerance and insulin sensitivity were normal. However, after high-fat diet feeding, the ZnT8(-/-) mice became glucose intolerant or diabetic, and islets became less responsive to glucose. Our data show that the ZnT8 transporter is essential for the formation of insulin crystals in beta cells, contributing to the packaging efficiency of stored insulin. Interaction between the ZnT8(-/-) genotype and diet to induce diabetes is a model for further studies of the mechanism of disease of human ZNT8 gene mutations.
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32
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Abstract
Glucose homeostasis is regulated primarily by the opposing actions of insulin and glucagon, hormones that are secreted by pancreatic islets from beta-cells and alpha-cells, respectively. Insulin secretion is increased in response to elevated blood glucose to maintain normoglycemia by stimulating glucose transport in muscle and adipocytes and reducing glucose production by inhibiting gluconeogenesis in the liver. Whereas glucagon secretion is suppressed by hyperglycemia, it is stimulated during hypoglycemia, promoting hepatic glucose production and ultimately raising blood glucose levels. Diabetic hyperglycemia occurs as the result of insufficient insulin secretion from the beta-cells and/or lack of insulin action due to peripheral insulin resistance. Remarkably, excessive secretion of glucagon from the alpha-cells is also a major contributor to the development of diabetic hyperglycemia. Insulin is a physiological suppressor of glucagon secretion; however, at the cellular and molecular levels, how intraislet insulin exerts its suppressive effect on the alpha-cells is not very clear. Although the inhibitory effect of insulin on glucagon gene expression is an important means to regulate glucagon secretion, recent studies suggest that the underlying mechanisms of the intraislet insulin on suppression of glucagon secretion involve the modulation of K(ATP) channel activity and the activation of the GABA-GABA(A) receptor system. Nevertheless, regulation of glucagon secretion is multifactorial and yet to be fully understood.
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Affiliation(s)
- Pritpal Bansal
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
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33
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Zhao Y, Fang Q, Straub SG, Sharp GWG. Both G i and G o heterotrimeric G proteins are required to exert the full effect of norepinephrine on the beta-cell K ATP channel. J Biol Chem 2007; 283:5306-16. [PMID: 18162464 DOI: 10.1074/jbc.m707695200] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The effects of norepinephrine (NE), an inhibitor of insulin secretion, were examined on membrane potential and the ATP-sensitive K+ channel (K ATP) in INS 832/13 cells. Membrane potential was monitored under the whole cell current clamp mode. NE hyperpolarized the cell membrane, an effect that was abolished by tolbutamide. The effect of NE on K ATP channels was investigated in parallel using outside-out single channel recording. This revealed that NE enhanced the open activities of the K ATP channels approximately 2-fold without changing the single channel conductance, demonstrating that NE-induced hyperpolarization was mediated by activation of the K ATP channels. The NE effect was abolished in cells preincubated with pertussis toxin, indicating coupling to heterotrimeric G i/G o proteins. To identify the G proteins involved, antisera raised against alpha and beta subunits (anti-G alpha common, anti-G beta, anti-G alpha i1/2/3, and anti-G alpha o) were used. Anti-G alpha common totally blocked the effects of NE on membrane potential and K ATP channels. Individually, anti-G alpha i1/2/3 and anti-G alpha o only partially inhibited the action of NE on K ATP channels. However, the combination of both completely eliminated the action. Antibodies against G beta had no effects. To confirm these results and to further identify the G protein subunits involved, the blocking effects of peptides containing the sequence of 11 amino acids at the C termini of the alpha subunits were used. The data obtained were similar to those derived from the antibody work with the additional information that G alpha i3 and G alpha o1 were not involved. In conclusion, both G i and G o proteins are required for the full effect of norepinephrine to activate the K ATP channel.
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Affiliation(s)
- Ying Zhao
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853-6401, USA
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34
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Zhou H, Zhang T, Harmon JS, Bryan J, Robertson RP. Zinc, not insulin, regulates the rat alpha-cell response to hypoglycemia in vivo. Diabetes 2007; 56:1107-12. [PMID: 17317764 DOI: 10.2337/db06-1454] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The intra-islet insulin hypothesis proposes that the decrement in beta-cell insulin secretion during hypoglycemia provides an activation signal for alpha-cells to release glucagon. A more recent hypothesis proposes that zinc atoms suppress glucagon secretion via their ability to open alpha-cell ATP-sensitive K(+) channels. Since insulin binds zinc, and zinc is co-secreted with insulin, we tested whether decreased zinc delivery to the alpha-cell activates glucagon secretion. In streptozotocin-induced diabetic Wistar rats, we observed that switching off intrapancreatic artery insulin infusions in vivo during hypoglycemia greatly improved glucagon secretion (area under the curve [AUC]: control group 240 +/- 261 and experimental group 4,346 +/- 1,259 pg x ml(-1) x 90 min(-1); n = 5, P < 0.02). Switching off pancreatic artery infusions of zinc chloride during hypoglycemia also improved the glucagon response (AUC: control group 817 +/- 107 and experimental group 3,445 +/- 573 pg x ml(-1) x 90 min(-1); n = 6, P < 0.01). However, switching off zinc-free insulin infusions had no effect. Studies of glucose uptake in muscle and liver cell lines verified that the zinc-free insulin was biologically active. We conclude that zinc atoms, not the insulin molecule itself, provide the switch-off signal from the beta-cell to the alpha-cell to initiate glucagon secretion during hypoglycemia.
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Affiliation(s)
- Huarong Zhou
- Pacific Northwest Research Institute, 720 Broadway, Seattle, WA 98122, USA
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35
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Gromada J, Franklin I, Wollheim CB. Alpha-cells of the endocrine pancreas: 35 years of research but the enigma remains. Endocr Rev 2007; 28:84-116. [PMID: 17261637 DOI: 10.1210/er.2006-0007] [Citation(s) in RCA: 424] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Glucagon, a hormone secreted from the alpha-cells of the endocrine pancreas, is critical for blood glucose homeostasis. It is the major counterpart to insulin and is released during hypoglycemia to induce hepatic glucose output. The control of glucagon secretion is multifactorial and involves direct effects of nutrients on alpha-cell stimulus-secretion coupling as well as paracrine regulation by insulin and zinc and other factors secreted from neighboring beta- and delta-cells within the islet of Langerhans. Glucagon secretion is also regulated by circulating hormones and the autonomic nervous system. In this review, we describe the components of the alpha-cell stimulus secretion coupling and how nutrient metabolism in the alpha-cell leads to changes in glucagon secretion. The islet cell composition and organization are described in different species and serve as a basis for understanding how the numerous paracrine, hormonal, and nervous signals fine-tune glucagon secretion under different physiological conditions. We also highlight the pathophysiology of the alpha-cell and how hyperglucagonemia represents an important component of the metabolic abnormalities associated with diabetes mellitus. Therapeutic inhibition of glucagon action in patients with type 2 diabetes remains an exciting prospect.
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Affiliation(s)
- Jesper Gromada
- Novartis Institutes for BioMedical Research, 100 Technology Square, Cambridge, Massachusetts 02139, USA.
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36
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Manning Fox JE, Gyulkhandanyan AV, Satin LS, Wheeler MB. Oscillatory membrane potential response to glucose in islet beta-cells: a comparison of islet-cell electrical activity in mouse and rat. Endocrinology 2006; 147:4655-63. [PMID: 16857746 DOI: 10.1210/en.2006-0424] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In contrast to mouse, rat islet beta-cell membrane potential is reported not to oscillate in response to elevated glucose despite demonstrated oscillations in calcium and insulin secretion. We aim to clarify the electrical activity of rat islet beta-cells and characterize and compare the electrical activity of both alpha- and beta-cells in rat and mouse islets. We recorded electrical activity from alpha- and beta-cells within intact islets from both mouse and rat using the perforated whole-cell patch clamp technique. Fifty-six percent of both mouse and rat beta-cells exhibited an oscillatory response to 11.1 mm glucose. Responses to both 11.1 mm and 2.8 mm glucose were identical in the two species. Rat beta-cells exhibited incremental depolarization in a glucose concentration-dependent manner. We also demonstrated electrical activity in human islets recorded under the same conditions. In both mouse and rat alpha-cells 11 mm glucose caused hyperpolarization of the membrane potential, whereas 2.8 mm glucose produced action potential firing. No species differences were observed in the response of alpha-cells to glucose. This paper is the first to demonstrate and characterize oscillatory membrane potential fluctuations in the presence of elevated glucose in rat islet beta-cells in comparison with mouse. The findings promote the use of rat islets in future electrophysiological studies, enabling consistency between electrophysiological and insulin secretion studies. An inverse response of alpha-cell membrane potential to glucose furthers our understanding of the mechanisms underlying glucose sensitive glucagon secretion.
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37
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Chimienti F, Devergnas S, Pattou F, Schuit F, Garcia-Cuenca R, Vandewalle B, Kerr-Conte J, Van Lommel L, Grunwald D, Favier A, Seve M. In vivo expression and functional characterization of the zinc transporter ZnT8 in glucose-induced insulin secretion. J Cell Sci 2006; 119:4199-206. [PMID: 16984975 DOI: 10.1242/jcs.03164] [Citation(s) in RCA: 245] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Insulin-secreting pancreatic beta cells are exceptionally rich in zinc. In these cells, zinc is required for zinc-insulin crystallization within secretory vesicles. Secreted zinc has also been proposed to be a paracrine and autocrine modulator of glucagon and insulin secretion in pancreatic alpha and beta cells, respectively. However, little is known about the molecular mechanisms underlying zinc accumulation in insulin-containing vesicles. We previously identified a pancreas-specific zinc transporter, ZnT-8, which colocalized with insulin in cultured beta cells. In this paper we studied its localization in human pancreatic islet cells, and its effect on cellular zinc content and insulin secretion. In human pancreatic islet cells, ZnT-8 was exclusively expressed in insulin-producing beta cells, and colocalized with insulin in these cells. ZnT-8 overexpression stimulated zinc accumulation and increased total intracellular zinc in insulin-secreting INS-1E cells. Furthermore, ZnT-8-overexpressing cells display enhanced glucose-stimulated insulin secretion compared with control cells, only for a high glucose challenge, i.e. >10 mM glucose. Altogether, these data strongly suggest that the zinc transporter ZnT-8 is a key protein for both zinc accumulation and regulation of insulin secretion in pancreatic beta cells.
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Affiliation(s)
- Fabrice Chimienti
- DRFMC/SCIB/LAN, UMR-E3 CEA/UJF, CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble CEDEX 9, France.
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38
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Bryan J, Muñoz A, Zhang X, Düfer M, Drews G, Krippeit-Drews P, Aguilar-Bryan L. ABCC8 and ABCC9: ABC transporters that regulate K+ channels. Pflugers Arch 2006; 453:703-18. [PMID: 16897043 DOI: 10.1007/s00424-006-0116-z] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2006] [Accepted: 06/08/2006] [Indexed: 11/28/2022]
Abstract
The sulfonylurea receptors (SURs) ABCC8/SUR1 and ABCC9/SUR2 are members of the C-branch of the transport adenosine triphosphatase superfamily. Unlike their brethren, the SURs have no identified transport function; instead, evolution has matched these molecules with K(+) selective pores, either K(IR)6.1/KCNJ8 or K(IR)6.2/KCNJ11, to assemble adenosine triphosphate (ATP)-sensitive K(+) channels found in endocrine cells, neurons, and both smooth and striated muscle. Adenine nucleotides, the major regulators of ATP-sensitive K(+) (K(ATP)) channel activity, exert a dual action. Nucleotide binding to the pore reduces the activity or channel open probability, whereas Mg-nucleotide binding and/or hydrolysis in the nucleotide-binding domains of SUR antagonize this inhibitory action to stimulate channel openings. Mutations in either subunit can alter this balance and, in the case of the SUR1/KIR6.2 channels found in neurons and insulin-secreting pancreatic beta cells, are the cause of monogenic forms of hyperinsulinemic hypoglycemia and neonatal diabetes. Additionally, the subtle dysregulation of K(ATP) channel activity by a K(IR)6.2 polymorphism has been suggested as a predisposing factor in type 2 diabetes mellitus. Studies on K(ATP) channel null mice are clarifying the roles of these metabolically sensitive channels in a variety of tissues.
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Affiliation(s)
- Joseph Bryan
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
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Takahashi R, Ishihara H, Tamura A, Yamaguchi S, Yamada T, Takei D, Katagiri H, Endou H, Oka Y. Cell type-specific activation of metabolism reveals that beta-cell secretion suppresses glucagon release from alpha-cells in rat pancreatic islets. Am J Physiol Endocrinol Metab 2006; 290:E308-16. [PMID: 16188913 DOI: 10.1152/ajpendo.00131.2005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Abnormal glucagon secretion is often associated with diabetes mellitus. However, the mechanisms by which nutrients modulate glucagon secretion remain poorly understood. Paracrine modulation by beta- or delta-cells is among the postulated mechanisms. Herein we present further evidence of the paracrine mechanism. First, to activate cellular metabolism and thus hormone secretion in response to specific secretagogues, we engineered insulinoma INS-1E cells using an adenovirus-mediated expression system. Expression of the Na+-dependent dicarboxylate transporter (NaDC)-1 resulted in 2.5- to 4.6-fold (P < 0.01) increases in insulin secretion in response to various tricarboxylic acid cycle intermediates. Similarly, expression of glycerol kinase (GlyK) increased insulin secretion 3.8- or 4.2-fold (P < 0.01) in response to glycerol or dihydroxyacetone, respectively. This cell engineering method was then modified, using the Cre-loxP switching system, to activate beta-cells and non-beta-cells separately in rat islets. NaDC-1 expression only in non-beta-cells, among which alpha-cells are predominant, caused an increase (by 1.8-fold, P < 0.05) in glucagon secretion in response to malate or succinate. However, the increase in glucagon release was prevented when NaDC-1 was expressed in whole islets, i.e., both beta-cells and non-beta-cells. Similarly, an increase in glucagon release with glycerol was observed when GlyK was expressed only in non-beta-cells but not when it was expressed in whole islets. Furthermore, dicarboxylates suppressed basal glucagon secretion by 30% (P < 0.05) when NaDC-1 was expressed only in beta-cells. These data demonstrate that glucagon secretion from rat alpha-cells depends on beta-cell activation and provide insights into the coordinated mechanisms underlying hormone secretion from pancreatic islets.
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Affiliation(s)
- Rui Takahashi
- Div. of Molecular Metabolism and Diabetes, Tohoku Univ. Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575, Japan
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40
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Muñoz A, Hu M, Hussain K, Bryan J, Aguilar-Bryan L, Rajan AS. Regulation of glucagon secretion at low glucose concentrations: evidence for adenosine triphosphate-sensitive potassium channel involvement. Endocrinology 2005; 146:5514-21. [PMID: 16123162 DOI: 10.1210/en.2005-0637] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Glucagon is a potent counterregulatory hormone that opposes the action of insulin in controlling glycemia. The cellular mechanisms by which pancreatic alpha-cell glucagon secretion occurs in response to hypoglycemia are poorly known. SUR1/K(IR)6.2-type ATP-sensitive K(+) (K(ATP)) channels have been implicated in the glucagon counterregulatory response at central and peripheral levels, but their role is not well understood. In this study, we examined hypoglycemia-induced glucagon secretion in vitro in isolated islets and in vivo using Sur1KO mice lacking neuroendocrine-type K(ATP) channels and paired wild-type (WT) controls. Sur1KO mice fed ad libitum have normal glucagon levels and mobilize hepatic glycogen in response to exogenous glucagon but exhibit a blunted glucagon response to insulin-induced hypoglycemia. Glucagon release from Sur1KO and WT islets is increased at 2.8 mmol/liter glucose and suppressed by increasing glucose concentrations. WT islets increase glucagon secretion approximately 20-fold when challenged with 0.1 mmol/liter glucose vs. approximately 2.7-fold for Sur1KO islets. Glucagon release requires Ca(2+) and is inhibited by nifedipine. Consistent with a regulatory interaction between K(ATP) channels and intra-islet zinc-insulin, WT islets exhibit an inverse correlation between beta-cell secretion and glucagon release. Glibenclamide stimulated insulin secretion and reduced glucagon release in WT islets but was without effect on secretion from Sur1KO islets. The results indicate that loss of alpha-cell K(ATP) channels uncouples glucagon release from inhibition by beta-cells and reveals a role for K(ATP) channels in the regulation of glucagon release by low glucose.
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Affiliation(s)
- Alvaro Muñoz
- Departments of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA
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41
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Franklin I, Gromada J, Gjinovci A, Theander S, Wollheim CB. Beta-cell secretory products activate alpha-cell ATP-dependent potassium channels to inhibit glucagon release. Diabetes 2005; 54:1808-15. [PMID: 15919803 DOI: 10.2337/diabetes.54.6.1808] [Citation(s) in RCA: 226] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Glucagon, secreted from islet alpha-cells, mobilizes liver glucose. During hyperglycemia, glucagon secretion is inhibited by paracrine factors from other islet cells, but in type 1 and type 2 diabetic patients, this suppression is lost. We investigated the effects of beta-cell secretory products zinc and insulin on isolated rat alpha-cells, intact islets, and perfused pancreata. Islet glucagon secretion was markedly zinc sensitive (IC(50) = 2.7 micromol/l) more than insulin release (IC(50) = 10.7 micromol/l). Glucose, the mitochondrial substrate pyruvate, and the ATP-sensitive K(+) channel (K(ATP) channel) inhibitor tolbutamide stimulated isolated alpha-cell electrical activity and glucagon secretion. Zinc opened K(ATP) channels and inhibited both electrical activity and pyruvate (but not arginine)-stimulated glucagon secretion in alpha-cells. Insulin transiently increased K(ATP) channel activity, inhibited electrical activity and glucagon secretion in alpha-cells, and inhibited pancreatic glucagon output. Insulin receptor and K(ATP) channel subunit transcripts were more abundant in alpha- than beta-cells. Transcript for the glucagon-like peptide 1 (GLP-1) receptor was not detected in alpha-cells nor did GLP-1 stimulate alpha-cell glucagon release. beta-Cell secretory products zinc and insulin therefore inhibit glucagon secretion most probably by direct activation of K(ATP) channels, thereby masking an alpha-cell metabolism secretion coupling pathway similar to beta-cells.
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Affiliation(s)
- Isobel Franklin
- Department of Cell PhysiologyMetabolism, University Medical Centre, 1211 Geneva 4, Switzerland
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Nikonenko I, Bancila M, Bloc A, Muller D, Bijlenga P. Inhibition of T-Type Calcium Channels Protects Neurons from Delayed Ischemia-Induced Damage. Mol Pharmacol 2005; 68:84-9. [PMID: 15851654 DOI: 10.1124/mol.104.010066] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Intracellular calcium increase is an early key event triggering ischemic neuronal cell damage. The role of T-type voltage-gated calcium channels in the neuronal response to ischemia, however, has never been studied. Using an in vitro model of ischemia-induced delayed cell death in rat organotypic hippocampal slice cultures, we show that T-type calcium channels inhibitors drastically reduce ischemic cell damage. Immunostaining studies reveal the existence of Ca(V)3.1 and Ca(V)3.2 types of low-voltage-activated calcium channels in rat organotypic hippocampal cultures. Low extracellular calcium (100 nM) or increase of intracellular calcium buffering ability by BAPTA-acetoxymethyl ester significantly reduced ischemia-induced neuronal damage. Pharmacological inhibition of the T-type calcium current by mibefradil, kurtoxin, nickel, zinc, and pimozide during the oxygen-glucose deprivation episode provided a significant protection against delayed neuronal death. Mibefradil and nickel exerted neuroprotective effects, not only if administrated during the oxygen-glucose deprivation episode but also in conditions of postischemic treatment. These data point to a role of T-type calcium currents in ischemia-induced, calcium-mediated neuronal cell damage and suggest a possible new pharmacological approach to stroke treatment.
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Affiliation(s)
- I Nikonenko
- Département des Neurosciences Cliniques, Hôpital Universitaire de Genève CH 1211 Genève, Suisse
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43
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Bancila V, Cens T, Monnier D, Chanson F, Faure C, Dunant Y, Bloc A. Two SUR1-specific Histidine Residues Mandatory for Zinc-induced Activation of the Rat KATP Channel. J Biol Chem 2005; 280:8793-9. [PMID: 15613469 DOI: 10.1074/jbc.m413426200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Zinc at micromolar concentrations hyperpolarizes rat pancreatic beta-cells and brain nerve terminals by activating ATP-sensitive potassium channels (KATP). The molecular determinants of this effect were analyzed using insulinoma cell lines and cells transfected with either wild type or mutated KATP subunits. Zinc activated KATP in cells co-expressing rat Kir6.2 and SUR1 subunits, as in insulinoma cell lines. In contrast, zinc exerted an inhibitory action on SUR2A-containing cells. Therefore, SUR1 expression is required for the activating action of zinc, which also depended on extracellular pH and was blocked by diethyl pyrocarbonate, suggesting histidine involvement. The five SUR1-specific extracellular histidine residues were submitted to site-directed mutagenesis. Of them, two histidines (His-326 and His-332) were found to be critical for the activation of KATP by zinc, as confirmed by the double mutation H326A/H332A. In conclusion, zinc activates KATP by binding itself to extracellular His-326 and His-332 of the SUR1 subunit. Thereby zinc could exert a negative control on cell excitability and secretion process of pancreatic beta-and alpha-cells. In fact, we have recently shown that such a mechanism occurs in hippocampal mossy fibers, a brain region characterized, like the pancreas, by an important accumulation of zinc and a high density of SUR1-containing KATP.
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Affiliation(s)
- Victor Bancila
- Neurosciences Fondamentales, CMU, 1 rue Michel Servet, 1211 Genève 04, Switzerland
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Prost AL, Bloc A, Hussy N, Derand R, Vivaudou M. Zinc is both an intracellular and extracellular regulator of KATP channel function. J Physiol 2004; 559:157-67. [PMID: 15218066 PMCID: PMC1665068 DOI: 10.1113/jphysiol.2004.065094] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Extracellular Zn(2+) has been identified as an activator of pancreatic K(ATP) channels. We further examined the action of Zn(2+) on recombinant K(ATP) channels formed with the inward rectifier K(+) channel subunit Kir6.2 associated with either the pancreatic/neuronal sulphonylurea receptor 1 (SUR1) subunit or the cardiac SUR2A subunit. Zn(2+), applied at either the extracellular or intracellular side of the membrane appeared as a potent, reversible activator of K(ATP) channels. External Zn(2+), at micromolar concentrations, activated SUR1/Kir6.2 but induced a small inhibition of SUR2A/Kir6.2 channels. Cytosolic Zn(2+) dose-dependently stimulated both SUR1/Kir6.2 and SUR2A/Kir6.2 channels, with half-maximal effects at 1.8 and 60 microm, respectively, but it did not affect the Kir6.2 subunit expressed alone. These observations point to an action of both external and internal Zn(2+) on the SUR subunit. Effects of internal Zn(2+) were not due to Zn(2+) leaking out, since they were unaffected by the presence of a Zn(2+) chelator on the external side. Similarly, internal chelators did not affect activation by external Zn(2+). Therefore, Zn(2+) is an endogenous K(ATP) channel opener being active on both sides of the membrane, with potentially distinct sites of action located on the SUR subunit. These findings uncover a novel regulatory pathway targeting K(ATP) channels, and suggest a new role for Zn(2+) as an intracellular signalling molecule.
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Affiliation(s)
- Anne-Lise Prost
- Biophysique Moléculaire & Cellulaire, CNRS UMR5090, CEA/DRDC, 17 rue des Martyrs, 38054 Grenoble, France
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Qian WJ, Gee KR, Kennedy RT. Imaging of Zn2+ release from pancreatic beta-cells at the level of single exocytotic events. Anal Chem 2004; 75:3468-75. [PMID: 14570199 DOI: 10.1021/ac0341057] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Regulated secretion of Zn2+ from isolated pancreatic beta-cells was imaged using laser-scanning confocal microscopy. In the method, beta-cells were incubated in a solution containing the novel fluorescent Zn2+ indicator FluoZin-3. Zn2+ released from the cells reacted with the dye to form a fluorescent product, which was detected by the confocal microscope. The new dye is much brighter than Zinquin, previously used for this application, allowing detection limits of 10-40 nM and temporal resolution of 16 ms/image. The high temporal resolution allowed imaging of isolated fluorescent transients that occurred at the edge of the cells following stimulation with 20 mM glucose or 40 mM K+. Fluorescent transients took 16-50 ms to reach a peak from the initial rise and returned to baseline after 170 +/- 50 ms (n = 78 transients from 15 cells). It was concluded that the transients correspond to detection of exocytotic release of Zn2+. Analysis of the temporal and spatial dispersion of the transients indicates that the release of Zn2+ is not diffusion limited but is instead kinetically controlled in agreement with previous observations of insulin release detected by amperometry.
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Affiliation(s)
- Wei-Jun Qian
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA
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46
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Yokoi K, Egger NG, Ramanujam VMS, Alcock NW, Dayal HH, Penland JG, Sandstead HH. Association between plasma zinc concentration and zinc kinetic parameters in premenopausal women. Am J Physiol Endocrinol Metab 2003; 285:E1010-20. [PMID: 12865259 DOI: 10.1152/ajpendo.00533.2002] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The objective of this study was to measure relationships between plasma zinc (Zn) concentrations and Zn kinetic parameters and to measure relationships of Zn status with taste acuity, food frequency, and hair Zn in humans. The subjects were 33 premenopausal women not taking oral contraceptives and dietary supplements containing iron and Zn. Main outcomes were plasma Zn concentrations, Zn kinetic parameters based on the three-compartment mammillary model using 67Zn as a tracer, electrical taste detection thresholds, and food frequencies. Lower plasma Zn was significantly (P < 0.01) associated with smaller sizes of the central and the lesser peripheral Zn pools, faster disappearance of tracer from plasma, and higher transfer rate constants from the lesser peripheral pool to the central pool and from the central pool to the greater peripheral pool. The break points in the plasma Zn-Zn kinetics relationship were found between 9.94 and 11.5 micromol/l plasma Zn. Smaller size of the lesser peripheral pool was associated with lower frequency of beef consumption and higher frequency of bran breakfast cereal consumption. Hypozincemic women with plasma Zn <10.7 micromol/l or 700 ng/ml had decreased thresholds of electrical stimulation for gustatory nerves. Our results based on Zn kinetics support the conventional cutoff value of plasma Zn (10.7 micromol/l or 700 ng/ml) between normal and low Zn status.
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Affiliation(s)
- Katsuhiko Yokoi
- Deptartment of Human Nutrition, Seitoku University Graduate School, Matsudo, Chiba 271-8555, Japan.
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Jeong SW, Park BG, Park JY, Lee JW, Lee JH. Divalent metals differentially block cloned T-type calcium channels. Neuroreport 2003; 14:1537-40. [PMID: 12960781 DOI: 10.1097/00001756-200308060-00028] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
We tested divalent metals including Cu2+, Pb2+, and Zn2+ to determine their pharmacological profiles for blockade of cloned T-type Ca2+ channels (alpha1G, alpha1 H, and alpha1I). Effects of the metals were also evaluated for native low and high voltage-activated Ca2+ channels in rat sympathetic pelvic neurons. Cu2+ and Zn2+ blocked three T-type channel isoforms in a concentration-dependent manner with a higher affinity for alpha1H currents (IC50 = 0.9 microM and 2.3 microM). In pelvic neurons, only Zn2+ showed strong selectivity for T-type Ca2+ currents over high voltage-activated Ca2+ currents. Conversely, Pb2+ block on Ca2+ channels did not show distinctive selectivity. Taken together, these results suggest that besides Ni2+, Cu2+ and Zn2+ can be used as selective blockers of alpha1 H at low concentrations.
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Affiliation(s)
- Seong-Woo Jeong
- Department of Physiology, Yonsei University, Wonju College of Medicine, Ilsan-Dong 162, Wonju, Kangwon-Do, Seoul, Korea
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Gee KR, Zhou ZL, Qian WJ, Kennedy R. Detection and imaging of zinc secretion from pancreatic beta-cells using a new fluorescent zinc indicator. J Am Chem Soc 2002; 124:776-8. [PMID: 11817952 DOI: 10.1021/ja011774y] [Citation(s) in RCA: 313] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A novel Zn2+-selective visible wavelength fluoroionophore (FluoZin-3, 9) was synthesized. The chelating portion of the molecule resembles known EGTA-based Ca2+-selective fluoroionophores, except that one of the N-acetic acid moieties has been deleted in 9. FluoZin-3 is virtually non-fluorescent in the absence of Zn2+, and exhibits a several hundred-fold fluorescence increase upon saturation with Zn2+( approximately 100 nM), with a Kd = 15 +/- 2 nM. A 1:1 binding stoichiometry of 9:Zn2+ was determined, and the fluorescence of the complex is pH-independent at pH > 6. FluoZin-3 was used to monitor Zn2+ that was co-secreted with insulin from pancreatic beta-cells by exocytosis following stimulation with glucose. The total Zn2+ concentration near the cells reached 600 nM, and Zn2+ was detectable at least 15 mum away from secreting cells. Heterogeneity in secretion among cells was indicated in that some cells in a cluster did not release Zn2+. Also, within secreting cells some regions of the cell membrane gave rise to secretion while others did not, suggesting active zones of secretion on the cell surface.
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Affiliation(s)
- Kyle R Gee
- Molecular Probes, Inc., 4849 Pitchford Avenue, Eugene, Oregon 97402, USA
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