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Harvey KE, Tang S, LaVigne EK, Pratt EPS, Hockerman GH. RyR2 regulates store-operated Ca2+ entry, phospholipase C activity, and electrical excitability in the insulinoma cell line INS-1. PLoS One 2023; 18:e0285316. [PMID: 37141277 PMCID: PMC10159205 DOI: 10.1371/journal.pone.0285316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Accepted: 04/19/2023] [Indexed: 05/05/2023] Open
Abstract
The ER Ca2+ channel ryanodine receptor 2 (RyR2) is required for maintenance of insulin content and glucose-stimulated insulin secretion, in part, via regulation of the protein IRBIT in the insulinoma cell line INS-1. Here, we examined store-operated and depolarization-dependent Ca2+entry using INS-1 cells in which either RyR2 or IRBIT were deleted. Store-operated Ca2+ entry (SOCE) stimulated with thapsigargin was reduced in RyR2KO cells compared to controls, but was unchanged in IRBITKO cells. STIM1 protein levels were not different between the three cell lines. Basal and stimulated (500 μM carbachol) phospholipase C (PLC) activity was also reduced specifically in RyR2KO cells. Insulin secretion stimulated by tolbutamide was reduced in RyR2KO and IRBITKO cells compared to controls, but was potentiated by an EPAC-selective cAMP analog in all three cell lines. Cellular PIP2 levels were increased and cortical f-actin levels were reduced in RyR2KO cells compared to controls. Whole-cell Cav channel current density was increased in RyR2KO cells compared to controls, and barium current was reduced by acute activation of the lipid phosphatase pseudojanin preferentially in RyR2KO cells over control INS-1 cells. Action potentials stimulated by 18 mM glucose were more frequent in RyR2KO cells compared to controls, and insensitive to the SK channel inhibitor apamin. Taken together, these results suggest that RyR2 plays a critical role in regulating PLC activity and PIP2 levels via regulation of SOCE. RyR2 also regulates β-cell electrical activity by controlling Cav current density and SK channel activation.
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Affiliation(s)
- Kyle E Harvey
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana, United States of America
| | - Shiqi Tang
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana, United States of America
| | - Emily K LaVigne
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana, United States of America
- Purdue Interdisciplinary Life Sciences Program, Purdue University, West Lafayette, Indiana, United States of America
| | - Evan P S Pratt
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana, United States of America
- Purdue Interdisciplinary Life Sciences Program, Purdue University, West Lafayette, Indiana, United States of America
| | - Gregory H Hockerman
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana, United States of America
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Postić S, Sarikas S, Pfabe J, Pohorec V, Križančić Bombek L, Sluga N, Skelin Klemen M, Dolenšek J, Korošak D, Stožer A, Evans-Molina C, Johnson JD, Slak Rupnik M. High-resolution analysis of the cytosolic Ca 2+ events in β cell collectives in situ. Am J Physiol Endocrinol Metab 2023; 324:E42-E55. [PMID: 36449570 PMCID: PMC9829482 DOI: 10.1152/ajpendo.00165.2022] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Revised: 11/15/2022] [Accepted: 11/22/2022] [Indexed: 12/02/2022]
Abstract
The release of peptide hormones is predominantly regulated by a transient increase in cytosolic Ca2+ concentration ([Ca2+]c). To trigger exocytosis, Ca2+ ions enter the cytosol from intracellular Ca2+ stores or from the extracellular space. The molecular events of late stages of exocytosis, and their dependence on [Ca2+]c, were extensively described in isolated single cells from various endocrine glands. Notably, less work has been done on endocrine cells in situ to address the heterogeneity of [Ca2+]c events contributing to a collective functional response of a gland. For this, β cell collectives in a pancreatic islet are particularly well suited as they are the smallest, experimentally manageable functional unit, where [Ca2+]c dynamics can be simultaneously assessed on both cellular and collective level. Here, we measured [Ca2+]c transients across all relevant timescales, from a subsecond to a minute time range, using high-resolution imaging with a low-affinity Ca2+ sensor. We quantified the recordings with a novel computational framework for automatic image segmentation and [Ca2+]c event identification. Our results demonstrate that under physiological conditions the duration of [Ca2+]c events is variable, and segregated into three reproducible modes, subsecond, second, and tens of seconds time range, and are a result of a progressive temporal summation of the shortest events. Using pharmacological tools we show that activation of intracellular Ca2+ receptors is both sufficient and necessary for glucose-dependent [Ca2+]c oscillations in β cell collectives, and that a subset of [Ca2+]c events could be triggered even in the absence of Ca2+ influx across the plasma membrane. In aggregate, our experimental and analytical platform was able to readily address the involvement of intracellular Ca2+ receptors in shaping the heterogeneity of [Ca2+]c responses in collectives of endocrine cells in situ.NEW & NOTEWORTHY Physiological glucose or ryanodine stimulation of β cell collectives generates a large number of [Ca2+]c events, which can be rapidly assessed with our newly developed automatic image segmentation and [Ca2+]c event identification pipeline. The event durations segregate into three reproducible modes produced by a progressive temporal summation. Using pharmacological tools, we show that activation of ryanodine intracellular Ca2+ receptors is both sufficient and necessary for glucose-dependent [Ca2+]c oscillations in β cell collectives.
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Affiliation(s)
- Sandra Postić
- Center for physiology and pharmacology, Medical University of Vienna, Vienna, Austria
| | - Srdjan Sarikas
- Center for physiology and pharmacology, Medical University of Vienna, Vienna, Austria
| | - Johannes Pfabe
- Center for physiology and pharmacology, Medical University of Vienna, Vienna, Austria
| | - Viljem Pohorec
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
| | | | - Nastja Sluga
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
| | - Maša Skelin Klemen
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
| | - Jurij Dolenšek
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
| | - Dean Korošak
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
- Faculty of Civil Engineering, Transportation Engineering and Architecture, University of Maribor, Maribor, Slovenia
| | - Andraž Stožer
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
| | - Carmella Evans-Molina
- Center for Diabetes and Metabolic Diseases and the Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, Indiana
- Richard L. Roudebush VA Medical Center, Indianapolis, Indiana
| | - James D Johnson
- Diabetes Research Group, Life Sciences Institute, Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - Marjan Slak Rupnik
- Center for physiology and pharmacology, Medical University of Vienna, Vienna, Austria
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
- Alma Mater Europaea-European Center Maribor, Maribor, Slovenia
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3
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RyR2/IRBIT regulates insulin gene transcript, insulin content, and secretion in the insulinoma cell line INS-1. Sci Rep 2022; 12:7713. [PMID: 35562179 PMCID: PMC9095623 DOI: 10.1038/s41598-022-11276-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Accepted: 03/31/2022] [Indexed: 12/01/2022] Open
Abstract
The role of ER Ca2+ release via ryanodine receptors (RyR) in pancreatic β-cell function is not well defined. Deletion of RyR2 from the rat insulinoma INS-1 (RyR2KO) enhanced IP3 receptor activity stimulated by 7.5 mM glucose, coincident with reduced levels of the protein IP3Receptor Binding protein released with Inositol 1,4,5 Trisphosphate (IRBIT). Insulin content, basal (2.5 mM glucose) and 7.5 mM glucose-stimulated insulin secretion were reduced in RyR2KO and IRBITKO cells compared to controls. INS2 mRNA levels were reduced in both RyR2KO and IRBITKO cells, but INS1 mRNA levels were specifically decreased in RyR2KO cells. Nuclear localization of S-adenosylhomocysteinase (AHCY) was increased in RyR2KO and IRBITKO cells. DNA methylation of the INS1 and INS2 gene promotor regions was very low, and not different among RyR2KO, IRBITKO, and controls, but exon 2 of the INS1 and INS2 genes was more extensively methylated in RyR2KO and IRBITKO cells. Exploratory proteomic analysis revealed that deletion of RyR2 or IRBIT resulted in differential regulation of 314 and 137 proteins, respectively, with 41 in common. These results suggest that RyR2 regulates IRBIT levels and activity in INS-1 cells, and together maintain insulin content and secretion, and regulate the proteome, perhaps via DNA methylation.
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Mansour A, Mohajeri-Tehrani MR, Samadi M, Qorbani M, Merat S, Adibi H, Poustchi H, Hekmatdoost A. Effects of supplementation with main coffee components including caffeine and/or chlorogenic acid on hepatic, metabolic, and inflammatory indices in patients with non-alcoholic fatty liver disease and type 2 diabetes: a randomized, double-blind, placebo-controlled, clinical trial. Nutr J 2021; 20:35. [PMID: 33838673 PMCID: PMC8037901 DOI: 10.1186/s12937-021-00694-5] [Citation(s) in RCA: 36] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Accepted: 04/03/2021] [Indexed: 11/15/2022] Open
Abstract
Background Non-alcoholic fatty liver disease (NAFLD) is much more frequent and more severe, including cirrhosis, hepatocellular carcinoma in patients with type 2 diabetes. Coffee is a complex beverage with hundreds of compounds whereas caffeine and chlorogenic acid are the most abundant bioactive compounds. The published epidemiological data demonstrating beneficial associations between all categories of coffee exposure and ranges of liver outcomes are rapidly growing; however, the main contributors and cause-effect relationships have not yet been elucidated. To address existing knowledge gaps, we sought to determine the efficacy and safety of 6 months chlorogenic acid and/or caffeine supplementation in patients with type 2 diabetes affected by NAFLD. Methods This trial was carried out at two Diabetes Centers to assess the effects of supplementation with daily doses of 200 mg chlorogenic acid, 200 mg caffeine, 200 mg chlorogenic acid plus 200 mg caffeine or placebo (starch) in patients with type 2 diabetes and NAFLD. The primary endpoint was reduction of hepatic fat and stiffness measured by FibroScan, and changes in serum hepatic enzymes and cytokeratin − 18 (CK-18) levels. Secondary endpoints were improvements in metabolic (including fasting glucose, homeostasis model assessment-estimated insulin resistance (HOMA-IR), hemoglobin A1c (HBA1C), C-peptide, insulin and lipid profiles) and inflammatory (including nuclear factor k-B (NF-KB), tumor necrosis factor (TNF-α), high sensitive- C reactive protein(hs-CRP)) parameters from baseline to the end of treatment. Results Neither chlorogenic acid nor caffeine was superior to placebo in attenuation of the hepatic fat and stiffness and other hepatic outcomes in patients with diabetes and NAFLD. Except for the lower level of total cholesterol in caffeine group (p = 0.04), and higher level of insulin in chlorogenic acid plus caffeine group (p = 0.01) compared with placebo, there were no significant differences among the treatment groups. Conclusion These findings do not recommend caffeine and/or chlorogenic acid to treat NAFLD in type 2 diabetes patients. Trial registration IRCT201707024010N21. Registered 14 September 2017.
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Affiliation(s)
- Asieh Mansour
- Department of Clinical Nutrition & Dietetics, Faculty of Nutrition Sciences and Food Technology, National Nutrition and Food Technology Research Institute, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Mohammad Reza Mohajeri-Tehrani
- Endocrinology and Metabolism Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran
| | - Majid Samadi
- Radiology Department, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran
| | - Mostafa Qorbani
- Non-communicable Diseases Research Center, Alborz University of Medical Sciences, Karaj, Iran.,Chronic Diseases Research Center, Endocrinology and Metabolism Population Sciences Institute, Endocrinology and Metabolism Research Institute, Tehran University of Medical Sciences, Tehran, Iran
| | - Shahin Merat
- Liver and Pancreatobiliary Diseases Research Center, Digestive Diseases Research Institute, Tehran University of Medical Sciences, Tehran, Iran
| | - Hossein Adibi
- Diabetes Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran
| | - Hossein Poustchi
- Liver and Pancreatobiliary Diseases Research Center, Digestive Diseases Research Institute, Tehran University of Medical Sciences, Tehran, Iran
| | - Azita Hekmatdoost
- Department of Clinical Nutrition & Dietetics, Faculty of Nutrition Sciences and Food Technology, National Nutrition and Food Technology Research Institute, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
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Expression of the Inositol 1,4,5-Trisphosphate Receptor and the Ryanodine Receptor Ca 2+-Release Channels in the Beta-Cells and Alpha-Cells of the Human Islets of Langerhans. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1131:271-279. [PMID: 31646514 DOI: 10.1007/978-3-030-12457-1_11] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Calcium signaling regulates secretion of hormones and many other cellular processes in the islets of Langerhans. The three subtypes of the inositol 1,4,5-trisphosphate receptors (IP3Rs), inositol 1,4,5-trisphosphate receptor type 1 (IP3R1), 1,4,5-trisphosphate receptor type 2 (IP3R2), 1,4,5-trisphosphate receptor type 3 (IP3R3), and the three subtypes of the ryanodine receptors (RyRs), ryanodine receptor 1 (RyR1), ryanodine receptor 2 (RyR2) and ryanodine receptor 3 (RyR3) are the main intracellular Ca2+-release channels. The identity and the relative levels of expression of these channels in the alpha-cells, and the beta-cells of the human islets of Langerhans are unknown. We have analyzed the RNA sequencing data obtained from highly purified human alpha-cells and beta-cells for quantitatively identifying the mRNA of the intracellular Ca2+-release channels in these cells. We found that among the three IP3Rs the IP3R3 is the most abundantly expressed one in the beta-cells, whereas IP3R1 is the most abundantly expressed one in the alpha-cells. In addition to the IP3R3, beta-cells also expressed the IP3R2, at a lower level. Among the RyRs, the RyR2 was the most abundantly expressed one in the beta-cells, whereas the RyR1 was the most abundantly expressed one in the alpha-cells. Information on the relative abundance of the different intracellular Ca2+-release channels in the human alpha-cells and the beta-cells may help the understanding of their roles in the generation of Ca2+ signals and many other related cellular processes in these cells.
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Islam MS. Stimulus-Secretion Coupling in Beta-Cells: From Basic to Bedside. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1131:943-963. [PMID: 31646540 DOI: 10.1007/978-3-030-12457-1_37] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Insulin secretion in humans is usually induced by mixed meals, which upon ingestion, increase the plasma concentration of glucose, fatty acids, amino acids, and incretins like glucagon-like peptide 1. Beta-cells can stay in the off-mode, ready-mode or on-mode; the mode-switching being determined by the open state probability of the ATP-sensitive potassium channels, and the activity of enzymes like glucokinase, and glutamate dehydrogenase. Mitochondrial metabolism is critical for insulin secretion. A sound understanding of the intermediary metabolism, electrophysiology, and cell signaling is essential for comprehension of the entire spectrum of the stimulus-secretion coupling. Depolarization brought about by inhibition of the ATP sensitive potassium channel, together with the inward depolarizing currents through the transient receptor potential (TRP) channels, leads to electrical activities, opening of the voltage-gated calcium channels, and exocytosis of insulin. Calcium- and cAMP-signaling elicited by depolarization, and activation of G-protein-coupled receptors, including the free fatty acid receptors, are intricately connected in the form of networks at different levels. Activation of the glucagon-like peptide 1 receptor augments insulin secretion by amplifying calcium signals by calcium induced calcium release (CICR). In the treatment of type 2 diabetes, use of the sulfonylureas that act on the ATP sensitive potassium channel, damages the beta cells, which eventually fail; these drugs do not improve the cardiovascular outcomes. In contrast, drugs acting through the glucagon-like peptide-1 receptor protect the beta-cells, and improve cardiovascular outcomes. The use of the glucagon-like peptide 1 receptor agonists is increasing and that of sulfonylurea is decreasing. A better understanding of the stimulus-secretion coupling may lead to the discovery of other molecular targets for development of drugs for the prevention and treatment of type 2 diabetes.
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Affiliation(s)
- Md Shahidul Islam
- Department of Clinical Science and Education, Södersjukhuset, Research Center, Karolinska Institutet, Stockholm, Sweden. .,Department of Emergency Care and Internal Medicine, Uppsala University Hospital, Uppsala University, Uppsala, Sweden.
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7
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Bruton J, Cheng AJ, Westerblad H. Measuring Ca 2+ in Living Cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1131:7-26. [PMID: 31646505 DOI: 10.1007/978-3-030-12457-1_2] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Measuring free Ca2+ concentration ([Ca2+]) in the cytosol or organelles is routine in many fields of research. The availability of membrane permeant forms of indicators coupled with the relative ease of transfecting cell lines with biological Ca2+ sensors have led to the situation where cellular and subcellular [Ca2+] is examined by many non-specialists. In this chapter, we evaluate the most used Ca2+ indicators and highlight what their major advantages and disadvantages are. We stress the potential pitfalls of non-ratiometric techniques for measuring Ca2+ and the clear advantages of ratiometric methods. Likely improvements and new directions for Ca2+ measurement are discussed.
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Affiliation(s)
- Joseph Bruton
- Department of Physiology & Pharmacology, Karolinska Institutet, Stockholm, Sweden.
| | - Arthur J Cheng
- Department of Physiology & Pharmacology, Karolinska Institutet, Stockholm, Sweden
| | - Håkan Westerblad
- Department of Physiology & Pharmacology, Karolinska Institutet, Stockholm, Sweden
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9
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Molecular regulation of insulin granule biogenesis and exocytosis. Biochem J 2017; 473:2737-56. [PMID: 27621482 DOI: 10.1042/bcj20160291] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Accepted: 04/19/2016] [Indexed: 12/15/2022]
Abstract
Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by hyperglycemia, insulin resistance and hyperinsulinemia in early disease stages but a relative insulin insufficiency in later stages. Insulin, a peptide hormone, is produced in and secreted from pancreatic β-cells following elevated blood glucose levels. Upon its release, insulin induces the removal of excessive exogenous glucose from the bloodstream primarily by stimulating glucose uptake into insulin-dependent tissues as well as promoting hepatic glycogenesis. Given the increasing prevalence of T2DM worldwide, elucidating the underlying mechanisms and identifying the various players involved in the synthesis and exocytosis of insulin from β-cells is of utmost importance. This review summarizes our current understanding of the route insulin takes through the cell after its synthesis in the endoplasmic reticulum as well as our knowledge of the highly elaborate network that controls insulin release from the β-cell. This network harbors potential targets for anti-diabetic drugs and is regulated by signaling cascades from several endocrine systems.
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Llanos P, Contreras-Ferrat A, Barrientos G, Valencia M, Mears D, Hidalgo C. Glucose-Dependent Insulin Secretion in Pancreatic β-Cell Islets from Male Rats Requires Ca2+ Release via ROS-Stimulated Ryanodine Receptors. PLoS One 2015; 10:e0129238. [PMID: 26046640 PMCID: PMC4457734 DOI: 10.1371/journal.pone.0129238] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Accepted: 05/06/2015] [Indexed: 12/03/2022] Open
Abstract
Glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells requires an increase in intracellular free Ca2+ concentration ([Ca2+]). Glucose uptake into β-cells promotes Ca2+ influx and reactive oxygen species (ROS) generation. In other cell types, Ca2+ and ROS jointly induce Ca2+ release mediated by ryanodine receptor (RyR) channels. Therefore, we explored here if RyR-mediated Ca2+ release contributes to GSIS in β-cell islets isolated from male rats. Stimulatory glucose increased islet insulin secretion, and promoted ROS generation in islets and dissociated β-cells. Conventional PCR assays and immunostaining confirmed that β-cells express RyR2, the cardiac RyR isoform. Extended incubation of β-cell islets with inhibitory ryanodine suppressed GSIS; so did the antioxidant N-acetyl cysteine (NAC), which also decreased insulin secretion induced by glucose plus caffeine. Inhibitory ryanodine or NAC did not affect insulin secretion induced by glucose plus carbachol, which engages inositol 1,4,5-trisphosphate receptors. Incubation of islets with H2O2 in basal glucose increased insulin secretion 2-fold. Inhibitory ryanodine significantly decreased H2O2-stimulated insulin secretion and prevented the 4.5-fold increase of cytoplasmic [Ca2+] produced by incubation of dissociated β-cells with H2O2. Addition of stimulatory glucose or H2O2 (in basal glucose) to β-cells disaggregated from islets increased RyR2 S-glutathionylation to similar levels, measured by a proximity ligation assay; in contrast, NAC significantly reduced the RyR2 S-glutathionylation increase produced by stimulatory glucose. We propose that RyR2-mediated Ca2+ release, induced by the concomitant increases in [Ca2+] and ROS produced by stimulatory glucose, is an essential step in GSIS.
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Affiliation(s)
- Paola Llanos
- Institute for Research in Dental Sciences, Facultad de Odontología, Universidad de Chile, Santiago, Chile
- Center of Molecular Studies of the Cell, Facultad de Medicina, Universidad de Chile, Santiago, Chile
- * E-mail: (PL); (CH)
| | - Ariel Contreras-Ferrat
- Institute for Research in Dental Sciences, Facultad de Odontología, Universidad de Chile, Santiago, Chile
- Center of Molecular Studies of the Cell, Facultad de Medicina, Universidad de Chile, Santiago, Chile
| | - Genaro Barrientos
- Physiology and Biophysics Program, Facultad de Medicina, Universidad de Chile, Santiago, Chile
| | - Marco Valencia
- Center of Molecular Studies of the Cell, Facultad de Medicina, Universidad de Chile, Santiago, Chile
| | - David Mears
- Center of Molecular Studies of the Cell, Facultad de Medicina, Universidad de Chile, Santiago, Chile
- Human Genetics Program, Institute of Biomedical Sciences, Facultad de Medicina, Universidad de Chile, Santiago, Chile
| | - Cecilia Hidalgo
- Center of Molecular Studies of the Cell, Facultad de Medicina, Universidad de Chile, Santiago, Chile
- Physiology and Biophysics Program, Facultad de Medicina, Universidad de Chile, Santiago, Chile
- Biomedical Neuroscience Institute, Facultad de Medicina, Universidad de Chile, Santiago, Chile
- * E-mail: (PL); (CH)
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Santulli G, Pagano G, Sardu C, Xie W, Reiken S, D'Ascia SL, Cannone M, Marziliano N, Trimarco B, Guise TA, Lacampagne A, Marks AR. Calcium release channel RyR2 regulates insulin release and glucose homeostasis. J Clin Invest 2015; 125:1968-78. [PMID: 25844899 DOI: 10.1172/jci79273] [Citation(s) in RCA: 146] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2014] [Accepted: 02/27/2015] [Indexed: 12/21/2022] Open
Abstract
The type 2 ryanodine receptor (RyR2) is a Ca2+ release channel on the endoplasmic reticulum (ER) of several types of cells, including cardiomyocytes and pancreatic β cells. In cardiomyocytes, RyR2-dependent Ca2+ release is critical for excitation-contraction coupling; however, a functional role for RyR2 in β cell insulin secretion and diabetes mellitus remains controversial. Here, we took advantage of rare RyR2 mutations that were identified in patients with a genetic form of exercise-induced sudden death (catecholaminergic polymorphic ventricular tachycardia [CPVT]). As these mutations result in a "leaky" RyR2 channel, we exploited them to assess RyR2 channel function in β cell dynamics. We discovered that CPVT patients with mutant leaky RyR2 present with glucose intolerance, which was heretofore unappreciated. In mice, transgenic expression of CPVT-associated RyR2 resulted in impaired glucose homeostasis, and an in-depth evaluation of pancreatic islets and β cells from these animals revealed intracellular Ca2+ leak via oxidized and nitrosylated RyR2 channels, activated ER stress response, mitochondrial dysfunction, and decreased fuel-stimulated insulin release. Additionally, we verified the effects of the pharmacological inhibition of intracellular Ca2+ leak in CPVT-associated RyR2-expressing mice, in human islets from diabetic patients, and in an established murine model of type 2 diabetes mellitus. Taken together, our data indicate that RyR2 channels play a crucial role in the regulation of insulin secretion and glucose homeostasis.
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Gilon P, Chae HY, Rutter GA, Ravier MA. Calcium signaling in pancreatic β-cells in health and in Type 2 diabetes. Cell Calcium 2014; 56:340-61. [DOI: 10.1016/j.ceca.2014.09.001] [Citation(s) in RCA: 116] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Revised: 08/26/2014] [Accepted: 09/01/2014] [Indexed: 12/24/2022]
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Lewarchik CM, Orabi AI, Jin S, Wang D, Muili KA, Shah AU, Eisses JF, Malik A, Bottino R, Jayaraman T, Husain SZ. The ryanodine receptor is expressed in human pancreatic acinar cells and contributes to acinar cell injury. Am J Physiol Gastrointest Liver Physiol 2014; 307:G574-81. [PMID: 25012845 PMCID: PMC4154117 DOI: 10.1152/ajpgi.00143.2014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Physiological calcium (Ca(2+)) signals within the pancreatic acinar cell regulate enzyme secretion, whereas aberrant Ca(2+) signals are associated with acinar cell injury. We have previously identified the ryanodine receptor (RyR), a Ca(2+) release channel on the endoplasmic reticulum, as a modulator of these pathological signals. In the present study, we establish that the RyR is expressed in human acinar cells and mediates acinar cell injury. We obtained pancreatic tissue from cadaveric donors and identified isoforms of RyR1 and RyR2 by qPCR. Immunofluorescence staining of the pancreas showed that the RyR is localized to the basal region of the acinar cell. Furthermore, the presence of RyR was confirmed from isolated human acinar cells by tritiated ryanodine binding. To determine whether the RyR is functionally active, mouse or human acinar cells were loaded with the high-affinity Ca(2+) dye (Fluo-4 AM) and stimulated with taurolithocholic acid 3-sulfate (TLCS) (500 μM) or carbachol (1 mM). Ryanodine (100 μM) pretreatment reduced the magnitude of the Ca(2+) signal and the area under the curve. To determine the effect of RyR blockade on injury, human acinar cells were stimulated with pathological stimuli, the bile acid TLCS (500 μM) or the muscarinic agonist carbachol (1 mM) in the presence or absence of the RyR inhibitor ryanodine. Ryanodine (100 μM) caused an 81% and 47% reduction in acinar cell injury, respectively, as measured by lactate dehydrogenase leakage (P < 0.05). Taken together, these data establish that the RyR is expressed in human acinar cells and that it modulates acinar Ca(2+) signals and cell injury.
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Affiliation(s)
| | | | | | | | - Kamaldeen A. Muili
- 3Department of Neurological Surgery, Comprehensive Cancer Center, Wexner Medical Center, Ohio State University, Columbus, Ohio;
| | | | | | | | - Rita Bottino
- 4Institute of Cellular Therapeutics, Allegheny General Hospital, Pittsburgh, Pennsylvania
| | - Thottala Jayaraman
- 2Dental Medicine, Children's Hospital of Pittsburgh of UPMC and the University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania;
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14
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Akash MSH, Rehman K, Chen S. Effects of coffee on type 2 diabetes mellitus. Nutrition 2014; 30:755-63. [DOI: 10.1016/j.nut.2013.11.020] [Citation(s) in RCA: 95] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2013] [Revised: 11/05/2013] [Accepted: 11/08/2013] [Indexed: 12/13/2022]
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Diaz-Sylvester PL, Porta M, Juettner VV, Lv Y, Fleischer S, Copello JA. Eudistomin D and penaresin derivatives as modulators of ryanodine receptor channels and sarcoplasmic reticulum Ca2+ ATPase in striated muscle. Mol Pharmacol 2014; 85:564-75. [PMID: 24423447 PMCID: PMC3965891 DOI: 10.1124/mol.113.089342] [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] [Received: 08/28/2013] [Accepted: 01/14/2014] [Indexed: 02/06/2023] Open
Abstract
Eudistomin D (EuD) and penaresin (Pen) derivatives are bioactive alkaloids from marine sponges found to induce Ca(2+) release from striated muscle sarcoplasmic reticulum (SR). Although these alkaloids are believed to affect ryanodine receptor (RyR) gating in a "caffeine-like" manner, no single-channel study confirmed this assumption. Here, EuD and MBED (9-methyl-7-bromoeudistomin D) were contrasted against caffeine on their ability to modulate the SR Ca(2+) loading/leak from cardiac and skeletal muscle SR microsomes as well as the function of RyRs in planar bilayers. The effects of these alkaloids on [(3)H]ryanodine binding and SR Ca(2+) ATPase (SERCA) activity were also tested. MBED (1-5 μM) fully mimicked maximal activating effects of caffeine (20 mM) on SR Ca(2+) leak. At the single-channel level, MBED mimicked the agonistic action of caffeine on cardiac RyR gating (i.e., stabilized long openings characteristic of "high-open-probability" mode). EuD was a partial agonist at the maximal doses tested. The tested Pen derivatives displayed mild to no agonism on RyRs, SR Ca(2+) leak, or [(3)H]ryanodine binding studies. Unlike caffeine, EuD and some Pen derivatives significantly inhibited SERCA at concentrations required to modulate RyRs. Instead, MBED's affinity for RyRs (EC50 ∼ 0.5 μM) was much larger than for SERCA (IC50 > 285 μM). In conclusion, MBED is a potent RyR agonist and, potentially, a better choice than caffeine for microsomal and cell studies due to its reported lack of effects on adenosine receptors and phosphodiesterases. As a high-affinity caffeine-like probe, MBED could also help identify the caffeine-binding site in RyRs.
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Affiliation(s)
- Paula L Diaz-Sylvester
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois (P.L.D.-S., V.V.J., Y.L., J.A.C.); Department of Physiology, Midwestern University, Chicago School of Osteopathic Medicine, Downers Grove, Illinois (M.P.); and Departments of Biological Sciences and Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee (S.F.)
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Induction and inhibition of an apparent neuronal phenotype in Spodoptera frugiperda insect cells (Sf21) by chemical agents. INVERTEBRATE NEUROSCIENCE 2012; 12:119-27. [PMID: 22797937 DOI: 10.1007/s10158-012-0138-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Accepted: 07/03/2012] [Indexed: 10/28/2022]
Abstract
The goal of this research was to induce neuron-like properties in Sf21 cells, an insect ovarian cell line, which could lead to a new high-throughput insecticide screening method and a way to mass produce insect neuronal material for basic research. This study applied differentiation agents to produce viable neuron-like cells. In the presence of the molting hormone 20-hydroxyecdysone (20-HE), or insulin, in the growth medium, a maximum of ca. 30 % of Sf21 cells expressed an apparent neuronal morphology of unipolar, bipolar, or multipolar axon-like processes within 2-3 days. Maximal differentiation occurred after 2 days in the presence of 50 μM 20-HE or 3 days in 10 μM insulin. Both 20-HE and insulin displayed time- and concentration-dependent differentiation with biphasic curves, suggesting that two binding sites or processes were contributing to the observed effects. In addition, combinations of 20-HE and insulin produced apparent synergistic effects on differentiation. Caffeine, a central nervous system stimulant, inhibited induction of elongated processes by 20-HE and/or insulin, with an IC(50) of 9 nM for 20-HE, and the inhibition was incomplete, resulting in about one-quarter of the differentiated cells remaining, even at high concentrations (up to 1 mM). The ability to induce a neural phenotype simplifies the studies of insect cells, compared to either the use of primary nervous tissue or genetic engineering techniques. The presence of ion channels or receptors in the differentiated cells remains to be determined.
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Abstract
Outside pregnancy, acute caffeine consumption is associated with insulin resistance. We investigated if during pregnancy plasma concentrations of caffeine and its metabolite, paraxanthine, were associated with insulin resistance. Caffeine, paraxanthine, glucose, and insulin were measured and insulin resistance estimated by homeostasis model assessment (HOMA) in banked samples from 251 fasting subjects at mean gestational age of 20.3 ± 2.0 weeks. Analysis of covariance and adjusted logistic regression were performed. Most (96.4%) women had caffeine and/or paraxanthine present. Caffeine concentrations in the upper two quartiles (>266 ng/mL) were associated with threefold higher odds of having higher insulin resistance estimated by log HOMA ≥75th percentile (third quartile odds ratio [OR], 3.02; 95% confidence interval [CI]: 1.21 to 7.54 and fourth quartile OR, 2.95; 95% CI: 1.19 to 7.31). Paraxanthine concentrations in the upper quartile (>392 ng/mL) were also associated with threefold higher odds of having higher insulin resistance (OR, 3.04; 95% CI: 1.28 to 7.25). Adjusted mean HOMA in the first caffeine-to-paraxanthine ratio quartile was 1.5 ± 2.2 versus 1.3 ± 2.3 in the fourth quartile ( P < 0.01). Both high caffeine and paraxanthine concentrations were associated with insulin resistance, but slow versus fast metabolism did not make an important difference.
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Affiliation(s)
- S. Katherine Laughon
- University of Pittsburgh Department of Obstetrics, Gynecology and Reproductive Services, University of Pittsburgh, Pittsburgh, PA
| | - Robert W. Powers
- University of Pittsburgh Department of Obstetrics, Gynecology and Reproductive Services, University of Pittsburgh, Pittsburgh, PA, Magee-Womens Research Institute, University of Pittsburgh, Pittsburgh, PA
| | - James M. Roberts
- University of Pittsburgh Department of Obstetrics, Gynecology and Reproductive Services, University of Pittsburgh, Pittsburgh, PA, Magee-Womens Research Institute, University of Pittsburgh, Pittsburgh, PA, Department of Epidemiology, University of Pittsburgh, Pittsburgh, PA, Clinical and Translational Research Institute, University of Pittsburgh, Pittsburgh, PA
| | - Sarah Parana
- Magee-Womens Research Institute, University of Pittsburgh, Pittsburgh, PA
| | - Janet Catov
- University of Pittsburgh Department of Obstetrics, Gynecology and Reproductive Services, University of Pittsburgh, Pittsburgh, PA, Magee-Womens Research Institute, University of Pittsburgh, Pittsburgh, PA, Department of Epidemiology, University of Pittsburgh, Pittsburgh, PA
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18
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Choi KJ, Cho DS, Kim JY, Kim BJ, Lee KM, Kim SH, Kim DK, Kim SH, Park HS. Ca-induced Ca Release from Internal Stores in INS-1 Rat Insulinoma Cells. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2011; 15:53-9. [PMID: 21461241 DOI: 10.4196/kjpp.2011.15.1.53] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Revised: 02/14/2011] [Accepted: 02/16/2011] [Indexed: 12/23/2022]
Abstract
The secretion of insulin from pancreatic β-cells is triggered by the influx of Ca(2+) through voltage-dependent Ca(2+) channels. The resulting elevation of intracellular calcium ([Ca(2+)](i)) triggers additional Ca(2+) release from internal stores. Less well understood are the mechanisms involved in Ca(2+) mobilization from internal stores after activation of Ca(2+) influx. The mobilization process is known as calcium-induced calcium release (CICR). In this study, our goal was to investigate the existence of and the role of caffeine-sensitive ryanodine receptors (RyRs) in a rat pancreatic β-cell line, INS-1 cells. To measure cytosolic and stored Ca(2+), respectively, cultured INS-1 cells were loaded with fura-2/AM or furaptra/AM. [Ca(2+)](i) was repetitively increased by caffeine stimulation in normal Ca(2+) buffer. However, peak [Ca(2+)](i) was only observed after the first caffeine stimulation in Ca(2+) free buffer and this increase was markedly blocked by ruthenium red, a RyR blocker. KCl-induced elevations in [Ca(2+)](i) were reduced by pretreatment with ruthenium red, as well as by depletion of internal Ca(2+) stores using cyclopiazonic acid (CPA) or caffeine. Caffeine-induced Ca(2+) mobilization ceased after the internal stores were depleted by carbamylcholine (CCh) or CPA. In permeabilized INS-1 cells, Ca(2+) release from internal stores was activated by caffeine, Ca(2+), or ryanodine. Furthermore, ruthenium red completely blocked the CICR response in permeabilized cells. RyRs were widely distributed throughout the intracellular compartment of INS-1 cells. These results suggest that caffeine-sensitive RyRs exist and modulate the CICR response from internal stores in INS-1 pancreatic β-cells.
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Affiliation(s)
- Kyung Jin Choi
- Department of Physiology, College of Medicine, Konyang University, Daejeon 302-718, Korea
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19
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Abstract
Methylxanthines of either natural or synthetic origin have a number of interesting pharmacological features. Proposed mechanisms of methylxanthine-induced pharmacological effects include competitive antagonism of G-coupled adenosine A(1) and A(2A) receptors and inhibition of phosphodiesterases. A number of studies have indicated that methylxanthines also exert effects through alternative mechanisms, in particular via activation of sarcoplasmic reticulum or endoplasmic reticulum ryanodine receptor (RyR) channels. More specifically, RyR channel activation by methylxanthines was reported (1) to stimulate the process of excitation coupling in muscle cells, (2) to augment the excitability of neurons and thus their capacity to release neurotransmitters, and also (3) to improve their survival. Here, we address the mechanisms by which methylxanthines control RyR activation and we consider the pharmacological consequences of this activation, in muscle and neuronal cells.
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Affiliation(s)
- Serge Guerreiro
- Centre de Recherche de l'Institut du Cerveau et de la Moelle Epinière, Université Pierre et Marie Curie-Paris 6, Paris, France
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20
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Islam MS. Calcium signaling in the islets. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 654:235-59. [PMID: 20217501 DOI: 10.1007/978-90-481-3271-3_11] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Easy access to rodent islets and insulinoma cells and the ease of measuring Ca(2+) by fluorescent indicators have resulted in an overflow of data that have clarified minute details of Ca(2+) signaling in the rodent islets. Our understanding of the mechanisms and the roles of Ca(2+) signaling in the human islets, under physiological conditions, has been hugely influenced by uncritical extrapolation of the rodent data obtained under suboptimal experimental conditions. More recently, electrophysiological and Ca(2+) studies have elucidated the ion channel repertoire relevant for Ca(2+) signaling in the human islets and have examined their relative importance. Many new channels belonging to the transient receptor potential (TRP) family are present in the beta-cells. Ryanodine receptors, nicotinic acid adenine dinucleotide phosphate channel, and Ca(2+)-induced Ca(2+) release add new dimension to the complexity of Ca(2+) signaling in the human beta-cells. A lot more needs to be learnt about the roles of these new channels and CICR, not because that will be easy but because that will be difficult. Much de-learning will also be needed. Human beta-cells do not have a resting state in the normal human body even under physiological fasting conditions. Their membrane potential under physiologically relevant resting conditions is approximately -50 mV. Biphasic insulin secretion is an experimental epiphenomenon unrelated to the physiological pulsatile insulin secretion into the portal vein in the human body. Human islets show a wide variety of electrical activities and patterns of [Ca(2+)](i) changes, whose roles in mediating pulsatile secretion of insulin into the portal vein remain questionable. Future studies will hopefully be directed toward a better understanding of Ca(2+) signaling in the human islets in the context of the pathogenesis and treatment of human diabetes.
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Affiliation(s)
- M Shahidul Islam
- Department of Clinical Sciences and Education, Södersjukhuset, Karolinska Institutet, Research Center, 118 83 Stockholm, Sweden.
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21
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beta-cell function in obese-hyperglycemic mice [ob/ob Mice]. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 654:463-77. [PMID: 20217510 DOI: 10.1007/978-90-481-3271-3_20] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
This review summarizes key aspects of what has been learned about the physiology of pancreatic islets and leptin deficiency from studies in obese ob/ob mice. ob/ob Mice lack functional leptin. They are grossly overweight and hyperphagic particularly at young ages and develop severe insulin resistance with hyperglycemia and hyperinsulinemia. ob/ob Mice have large pancreatic islets. The beta-cells respond adequately to most stimuli, and ob/ob mice have been used as a rich source of pancreatic islets with high insulin release capacity. ob/ob Mice can perhaps be described as a model for the prediabetic state. The large capacity for islet growth and insulin release makes ob/ob mice a good model for studies on how beta-cells can cope with prolonged functional stress.
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Abstract
The versatility of Ca(2+) as an intracellular messenger derives largely from the spatial organization of cytosolic Ca(2+) signals, most of which are generated by regulated openings of Ca(2+)-permeable channels. Most Ca(2+) channels are expressed in the plasma membrane (PM). Others, including the almost ubiquitous inositol 1,4,5-trisphosphate receptors (IP(3)R) and their relatives, the ryanodine receptors (RyR), are predominantly expressed in membranes of the sarcoplasmic or endoplasmic reticulum (ER). Targeting of these channels to appropriate destinations underpins their ability to generate spatially organized Ca(2+) signals. All Ca(2+) channels begin life in the cytosol, and the vast majority are then functionally assembled in the ER, where they may either remain or be dispatched to other membranes. Here, by means of selective examples, we review two issues related to this trafficking of Ca(2+) channels via the ER. How do cells avoid wayward activity of Ca(2+) channels in transit as they pass from the ER via other membranes to their final destination? How and why do some cells express small numbers of the archetypal intracellular Ca(2+) channels, IP(3)R and RyR, in the PM?
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Affiliation(s)
- Colin W Taylor
- Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, UK.
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Chen Z, Li Z, Wei B, Yin W, Xu T, Kotlikoff MI, Ji G. FKBP12.6-knockout mice display hyperinsulinemia and resistance to high-fat diet-induced hyperglycemia. FASEB J 2009; 24:357-63. [PMID: 19805579 DOI: 10.1096/fj.09-138446] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
FK506 binding protein 12.6 kDa (FKBP12.6), a protein that regulates ryanodine Ca(2+) release channels, may act as an important regulator of insulin secretion. In this study, the role of FKBP12.6 in the control of insulin secretion and blood glucose is clarified using FKBP12.6(-/-) mice. FKBP12.6(-/-) mice showed significant fed hyperinsulinemia but exhibited normoglycemia, fasting normoinsulinemia, and normal body weight compared with wild-type (WT) littermate control mice. Deletion of FKBP12.6 resulted in enhanced glucose-stimulated insulin secretion (GSIS) both in vivo and in vitro, a result that is due to enhanced glucose-induced islet Ca(2+) elevation. After a high-fat dietary challenge (HF diet) for 3 mo, FKBP12.6(-/-) mice displayed higher body weight, hyperinsulinemia, and lower fed blood glucose concentrations compared with WT mice. FKBP12.6(-/-) mice displayed hyperinsulinemia, and resistance to HF diet-induced hyperglycemia, suggesting that FKBP12.6 plays an important role in insulin secretion and blood glucose control, and raising the possibility that it may be a potential therapeutic target for the treatment of type 2 diabetes.
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Affiliation(s)
- Zheng Chen
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
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24
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Li F, Zhang ZM. Comparative identification of Ca2+ channel expression in INS-1 and rat pancreatic beta cells. World J Gastroenterol 2009; 15:3046-50. [PMID: 19554659 PMCID: PMC2702114 DOI: 10.3748/wjg.15.3046] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
AIM To identify and compare the profile of Ca(2+) channel subunit expression in INS-1 and rat pancreatic beta cells. METHODS The rat insulin-secreting INS-1 cell line was cultured in RPMI-1640 with Wistar rats employed as islet donors. Ca(2+) channel subunit expression in INS-1 and isolated rat beta cells were examined by reverse transcription polymerase chain reaction (RT-PCR). Absolute real-time quantitative PCR was performed in a Bio-Rad iQ5 Gradient Real Time PCR system and the data analyzed using an iQ5 system to identify the expression level of the Ca(2+) channel subunits. RESULTS In INS-1 cells, the L-type Ca(2+) channel 1C subunit had the highest expression level and the TPRM2 subunit had the second highest expression. In rat beta cells, the TPRC4beta subunit expression was dominant and the expression of the L-type 1C subunit exceeded the 1D subunit expression about two-fold. This result agreed with other studies, confirming the important role of the L-type 1C subunit in insulin-secreting cells, and suggested that non-voltage-operated Ca(2+) channels may have an important role in biphasic insulin secretion. CONCLUSION Twelve major Ca(2+) channel subunit types were identified in INS-1 and rat beta cells and significant differences were observed in the expression of certain subunits between these cells.
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Affiliation(s)
- Fei Li
- Department of General Surgery, Digestive Medical Center, The First Affiliated Hospital, Medical School, Tsinghua University, Beijing, China
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25
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Bari MR, Akbar S, Eweida M, Kühn FJP, Gustafsson AJ, Lückhoff A, Islam MS. H2O2-induced Ca2+ influx and its inhibition by N-(p-amylcinnamoyl) anthranilic acid in the beta-cells: involvement of TRPM2 channels. J Cell Mol Med 2009. [PMID: 19382906 DOI: 10.1111/j.1582‐4934.2009.00737.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Type 2 melastatin-related transient receptor potential channel (TRPM2), a member of the melastatin-related TRP (transient receptor potential) subfamily is a Ca(2+)-permeable channel activated by hydrogen peroxide (H(2)O(2)). We have investigated the role of TRPM2 channels in mediating the H(2)O(2)-induced increase in the cytoplasmic free Ca(2+) concentration ([Ca(2+)](i)) in insulin-secreting cells. In fura-2 loaded INS-1E cells, a widely used model of beta-cells, and in human beta-cells, H(2)O(2) increased [Ca(2+)](i), in the presence of 3 mM glucose, by inducing Ca(2+) influx across the plasma membrane. H(2)O(2)-induced Ca(2+) influx was not blocked by nimodipine, a blocker of the L-type voltage-gated Ca(2+) channels nor by 2-aminoethoxydiphenyl borate, a blocker of several TRP channels and store-operated channels, but it was completely blocked by N-(p-amylcinnamoyl)anthranilic acid (ACA), a potent inhibitor of TRPM2. Adenosine diphosphate phosphate ribose, a specific activator of TRPM2 channel and H(2)O(2), induced inward cation currents that were blocked by ACA. Western blot using antibodies directed to the epitopes on the N-terminal and on the C-terminal parts of TRPM2 identified the full length TRPM2 (TRPM2-L), and the C-terminally truncated TRPM2 (TRPM2-S) in human islets. We conclude that functional TRPM2 channels mediate H(2)O(2)-induced Ca(2+) entry in beta-cells, a process potently inhibited by ACA.
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Affiliation(s)
- Muhammad R Bari
- Department of Clinical Sciences and Education, Karolinska Institutet, Research Centre, Stockholm South Hospital, Stockholm, Sweden
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26
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Bari MR, Akbar S, Eweida M, Kühn FJP, Gustafsson AJ, Lückhoff A, Islam MS. H2O2-induced Ca2+ influx and its inhibition by N-(p-amylcinnamoyl) anthranilic acid in the beta-cells: involvement of TRPM2 channels. J Cell Mol Med 2009; 13:3260-7. [PMID: 19382906 PMCID: PMC4516483 DOI: 10.1111/j.1582-4934.2009.00737.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Type 2 melastatin-related transient receptor potential channel (TRPM2), a member of the melastatin-related TRP (transient receptor potential) subfamily is a Ca(2+)-permeable channel activated by hydrogen peroxide (H(2)O(2)). We have investigated the role of TRPM2 channels in mediating the H(2)O(2)-induced increase in the cytoplasmic free Ca(2+) concentration ([Ca(2+)](i)) in insulin-secreting cells. In fura-2 loaded INS-1E cells, a widely used model of beta-cells, and in human beta-cells, H(2)O(2) increased [Ca(2+)](i), in the presence of 3 mM glucose, by inducing Ca(2+) influx across the plasma membrane. H(2)O(2)-induced Ca(2+) influx was not blocked by nimodipine, a blocker of the L-type voltage-gated Ca(2+) channels nor by 2-aminoethoxydiphenyl borate, a blocker of several TRP channels and store-operated channels, but it was completely blocked by N-(p-amylcinnamoyl)anthranilic acid (ACA), a potent inhibitor of TRPM2. Adenosine diphosphate phosphate ribose, a specific activator of TRPM2 channel and H(2)O(2), induced inward cation currents that were blocked by ACA. Western blot using antibodies directed to the epitopes on the N-terminal and on the C-terminal parts of TRPM2 identified the full length TRPM2 (TRPM2-L), and the C-terminally truncated TRPM2 (TRPM2-S) in human islets. We conclude that functional TRPM2 channels mediate H(2)O(2)-induced Ca(2+) entry in beta-cells, a process potently inhibited by ACA.
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Affiliation(s)
- Muhammad R Bari
- Department of Clinical Sciences and Education, Karolinska Institutet, Research Centre, Stockholm South Hospital, Stockholm, Sweden
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27
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Ferraz GC, Teixeira-Neto AR, Lacerda-Neto JC, Pereira GT, Queiroz-Neto A. Aminophylline Affects Glycemia Control and Increases Anaerobic Glycolysis in Horses during Incremental Exercise. J Equine Vet Sci 2008. [DOI: 10.1016/j.jevs.2008.05.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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28
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Noguchi N, Yoshikawa T, Ikeda T, Takahashi I, Shervani NJ, Uruno A, Yamauchi A, Nata K, Takasawa S, Okamoto H, Sugawara A. FKBP12.6 disruption impairs glucose-induced insulin secretion. Biochem Biophys Res Commun 2008; 371:735-40. [PMID: 18466757 DOI: 10.1016/j.bbrc.2008.04.142] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2008] [Accepted: 04/25/2008] [Indexed: 11/25/2022]
Abstract
Cyclic ADP-ribose (cADPR), accumulated in pancreatic beta-cells in response to elevated ATP levels after glucose stimulation, mobilizes Ca(2+) from the endoplasmic reticulum through the ryanodine receptor (RyR) and thereby induces insulin secretion. We have recently demonstrated in an in vitro study that cADPR activates RyR through binding to FK506-binding protein 12.6 (FKBP12.6), an accessory protein of RyR. Here we generated FKBP12.6-deficient (FKBP12.6(-/-)) mice by homologous recombination. FKBP12.6(-/-) mice showed glucose intolerance coupled to insufficient insulin secretion upon a glucose challenge. Insulin secretion in response to glucose was markedly impaired in FKBP12.6(-/-) islets, while sulfonylurea- or KCl-induced insulin secretion was unaffected. No difference was found in the glucose oxidation rate between FKBP12.6(-/-) and wild-type islets. These results indicate that FKBP12.6 plays a role in glucose-induced insulin secretion downstream of ATP production, independently of ATP-sensitive K(+) channels, in pancreatic beta-cells.
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Affiliation(s)
- Naoya Noguchi
- Department of Advanced Biological Sciences for Regeneration (Kotobiken Medical Laboratories), Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Sendai 980-8575, Japan
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Doyle ME, Egan JM. Mechanisms of action of glucagon-like peptide 1 in the pancreas. Pharmacol Ther 2007; 113:546-93. [PMID: 17306374 PMCID: PMC1934514 DOI: 10.1016/j.pharmthera.2006.11.007] [Citation(s) in RCA: 474] [Impact Index Per Article: 27.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2006] [Accepted: 11/27/2006] [Indexed: 12/13/2022]
Abstract
Glucagon-like peptide 1 (GLP-1) is a hormone that is encoded in the proglucagon gene. It is mainly produced in enteroendocrine L cells of the gut and is secreted into the blood stream when food containing fat, protein hydrolysate, and/or glucose enters the duodenum. Its particular effects on insulin and glucagon secretion have generated a flurry of research activity over the past 20 years culminating in a naturally occurring GLP-1 receptor (GLP-1R) agonist, exendin 4 (Ex-4), now being used to treat type 2 diabetes mellitus (T2DM). GLP-1 engages a specific guanine nucleotide-binding protein (G-protein) coupled receptor (GPCR) that is present in tissues other than the pancreas (brain, kidney, lung, heart, and major blood vessels). The most widely studied cell activated by GLP-1 is the insulin-secreting beta cell where its defining action is augmentation of glucose-induced insulin secretion. Upon GLP-1R activation, adenylyl cyclase (AC) is activated and cAMP is generated, leading, in turn, to cAMP-dependent activation of second messenger pathways, such as the protein kinase A (PKA) and Epac pathways. As well as short-term effects of enhancing glucose-induced insulin secretion, continuous GLP-1R activation also increases insulin synthesis, beta cell proliferation, and neogenesis. Although these latter effects cannot be currently monitored in humans, there are substantial improvements in glucose tolerance and increases in both first phase and plateau phase insulin secretory responses in T2DM patients treated with Ex-4. This review will focus on the effects resulting from GLP-1R activation in the pancreas.
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Affiliation(s)
- Máire E Doyle
- Department of Pathology, Immunology & Laboratory Medicine, College of Medicine, University of Florida, Gainesville, FL, USA
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Zhang F, Zhang Q, Tengholm A, Sjöholm A. Involvement of JAK2 and Src kinase tyrosine phosphorylation in human growth hormone-stimulated increases in cytosolic free Ca2+and insulin secretion. Am J Physiol Cell Physiol 2006; 291:C466-75. [PMID: 16597920 DOI: 10.1152/ajpcell.00418.2005] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
We previously reported that human growth hormone (hGH) increases cytoplasmic Ca2+concentration ([Ca2+]i) and proliferation in pancreatic β-cells (Sjöholm Å, Zhang Q, Welsh N, Hansson A, Larsson O, Tally M, and Berggren PO. J Biol Chem 275: 21033–21040, 2000) and that the hGH-induced rise in [Ca2+]iinvolves Ca2+-induced Ca2+release facilitated by tyrosine phosphorylation of ryanodine receptors (Zhang Q, Kohler M, Yang SN, Zhang F, Larsson O, and Berggren PO. Mol Endocrinol 18: 1658–1669, 2004). Here we investigated the tyrosine kinases that convey the hGH-induced rise in [Ca2+]iand insulin release in BRIN-BD11 β-cells. hGH caused tyrosine phosphorylation of Janus kinase (JAK)2 and c-Src, events inhibited by the JAK2 inhibitor AG490 or the Src kinase inhibitor PP2. Although hGH-stimulated rises in [Ca2+]iand insulin secretion were completely abolished by AG490 and JAK2 inhibitor II, the inhibitors had no effect on insulin secretion stimulated by a high K+concentration. Similarly, Src kinase inhibitor-1 and PP2, but not its inactive analog PP3, suppressed [Ca2+]ielevation and completely abolished insulin secretion stimulated by hGH but did not affect responses to K+. Ovine prolactin increased [Ca2+]iand insulin secretion to a similar extent as hGH, effects prevented by the JAK2 and Src kinase inhibitors. In contrast, bovine GH evoked a rise in [Ca2+]ibut did not stimulate insulin secretion. Neither JAK2 nor Src kinase inhibitors influenced the effect of bovine GH on [Ca2+]i. Our study indicates that hGH stimulates rise in [Ca2+]iand insulin secretion mainly through activation of the prolactin receptor and JAK2 and Src kinases in rat insulin-secreting cells.
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Affiliation(s)
- Fan Zhang
- Research Center, Karolinska Institute, Stockholm South Hospital, SE-11883 Stockholm, Sweden
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Shigeto M, Katsura M, Matsuda M, Ohkuma S, Kaku K. First phase of glucose-stimulated insulin secretion from MIN 6 cells does not always require extracellular calcium influx. J Pharmacol Sci 2006; 101:293-302. [PMID: 16891769 DOI: 10.1254/jphs.fp0060057] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
To demonstrate an involvement of ATP-sensitive potassium (K(ATP)) channel-independent pathways in the first phase of glucose-stimulated insulin secretion (GSIS) from pancreatic beta cells, the time course of GSIS from MIN6 cells was analyzed at 30-s sample intervals. GSIS was biphasic with the first phase being observed 120 to 390 s after glucose addition, peaking at 180 s, and with a shoulder at 240 to 330 s. Both 10 microM diazoxide and 3 microM verapamil completely inhibited tolbutamide- or glibenclamide-induced insulin secretion and suppressed the peak of the first phase of GSIS, but did not result in complete suppression. The shoulder following the peak was suppressed by 1 muM dantrolene. The peak, but not shoulder, disappeared under the extracellular Ca2+-free condition. A significant amount of insulin secretion remained even in the combined presence of verapamil and dantrolene. The Na+ channel blocker tetrodotoxin (30 nM) nearly completely inhibited the first phase release. These results suggest that the first phase of GSIS from MIN6 cells depends on both Ca2+-dependent and -independent mechanisms. The former mechanism includes the extracellular Ca2+ influx via L-type voltage-dependent calcium channel and intracellular Ca2+ release from endoplasmic reticulum via ryanodine receptors, and the latter mechanism involves the pathways associated with Na+ channels.
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Affiliation(s)
- Makoto Shigeto
- Division of Diabetes and Endocrinology, Department of Medicine, Kawasaki Medical School, Kurashiki, Okayama, Japan
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Liu G, Jacobo SMP, Hilliard N, Hockerman GH. Differential modulation of Cav1.2 and Cav1.3-mediated glucose-stimulated insulin secretion by cAMP in INS-1 cells: distinct roles for exchange protein directly activated by cAMP 2 (Epac2) and protein kinase A. J Pharmacol Exp Ther 2006; 318:152-60. [PMID: 16565168 DOI: 10.1124/jpet.105.097477] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Using insulin-secreting cell line (INS)-1 cells stably expressing dihydropyridine-insensitive mutants of either Cav1.2 or Cav1.3, we previously demonstrated that Cav1.3 is preferentially coupled to insulin secretion and [Ca2+]i oscillations stimulated by 11.2 mM glucose. Using the same system, we found that insulin secretion in 7.5 mM glucose plus 1 mM 8-bromo-cAMP (8-Br-cAMP) is mediated by both Cav1.2 and Cav1.3. Treatment of INS-1 cells or INS-1 cells stably expressing Cav1.2/dihydropyridine-insensitive (DHPi) channels in the presence of 10 microM nifedipine, with effector-specific cAMP analogs 8-(4-chlorophenylthio)-2'-O-methyladenosine-cAMP [8-pCPT-2'-O-Me-cAMP; 100 microM; Exchange Protein directly Activated by cAMP 2 (Epac2)-selective] or N6-benzoyl-cAMP [50 microM; Protein Kinase A (PKA)-selective] partially increased insulin secretion. Secretion stimulated by a combination of the two cAMP analogs was additive and comparable with that stimulated by 1 mM 8-Br-cAMP. In INS-1 cells stably expressing Cav1.3/DHPi in the presence of 10 microM nifedipine, N6-benzoyl-cAMP, but not 8-pCPT-2'-O-Me-cAMP, significantly increased glucose-stimulated insulin secretion. However, the combination of N6-benzoyl-cAMP and 8-pCPT-2'-O-Me-cAMP significantly increased glucose-stimulated secretion compared with N6-benzoyl-cAMP alone. In INS-1 cells, 8-Br-cAMP potentiation of insulin secretion in 7.5 mM glucose is blocked by thapsigargin (1 microM) and ryanodine (0.5 microM). In contrast, ryanodine has no effect on insulin secretion or [Ca2+]i oscillations stimulated by 11.2 mM glucose in INS-1 cells. Our data suggest that both Cav1.2 and Cav1.3 mediate insulin secretion stimulated by 7.5 mM glucose and cAMP via a mechanism that requires internal stores of Ca2+. Furthermore, cAMP modulation of secretion mediated by Cav1.2 seems to involve both Epac2 and PKA independently. In contrast, cAMP modulation of Cav1.3-mediated secretion depends upon PKA activation, whereas the contribution of Epac2 is dependent upon PKA activation.
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Affiliation(s)
- Guohong Liu
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, 575 Stadium Mall Drive, West Lafayette, IN 47907-2091, USA
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Kang G, Chepurny OG, Rindler MJ, Collis L, Chepurny Z, Li WH, Harbeck M, Roe MW, Holz GG. A cAMP and Ca2+ coincidence detector in support of Ca2+-induced Ca2+ release in mouse pancreatic beta cells. J Physiol 2005; 566:173-88. [PMID: 15860526 PMCID: PMC3583090 DOI: 10.1113/jphysiol.2005.087510] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/26/2005] [Indexed: 11/08/2022] Open
Abstract
The blood glucose-lowering hormone glucagon-like peptide-1 (GLP-1) stimulates cAMP production, promotes Ca2+ influx, and mobilizes an intracellular source of Ca2+ in pancreatic beta cells. Here we provide evidence that these actions of GLP-1 are functionally related: they reflect a process of Ca2+-induced Ca2+ release (CICR) that requires activation of protein kinase A (PKA) and the Epac family of cAMP-regulated guanine nucleotide exchange factors (cAMPGEFs). In rat insulin-secreting INS-1 cells or mouse beta cells loaded with caged Ca2+ (NP-EGTA), a GLP-1 receptor agonist (exendin-4) is demonstrated to sensitize intracellular Ca2+ release channels to stimulatory effects of cytosolic Ca2+, thereby allowing CICR to be generated by the uncaging of Ca2+ (UV flash photolysis). This sensitizing action of exendin-4 is diminished by an inhibitor of PKA (H-89) or by overexpression of dominant negative Epac. It is reproduced by cell-permeant cAMP analogues that activate PKA (6-Bnz-cAMP) or Epac (8-pCPT-2'-O-Me-cAMP) selectively. Depletion of Ca2+ stores with thapsigargin abolishes CICR, while inhibitors of Ca2+ release channels (ryanodine and heparin) attenuate CICR in an additive manner. Because the uncaging of Ca2+ fails to stimulate CICR in the absence of cAMP-elevating agents, it is concluded that there exists in beta cells a process of second messenger coincidence detection, whereby intracellular Ca2+ release channels (ryanodine receptors, inositol 1,4,5-trisphosphate (IP3) receptors) monitor a simultaneous increase of cAMP and Ca2+ concentrations. We propose that second messenger coincidence detection of this type may explain how GLP-1 interacts with beta cell glucose metabolism to stimulate insulin secretion.
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Affiliation(s)
- Guoxin Kang
- Department of Physiology and Neuroscience, New York University School of MedicineNew York, NY 10016, USA
| | - Oleg G Chepurny
- Department of Physiology and Neuroscience, New York University School of MedicineNew York, NY 10016, USA
| | - Michael J Rindler
- Department of Cell Biology, New York University School of MedicineNew York, NY 10016, USA
| | - Leon Collis
- Department of Cardiology, New York University School of MedicineNew York, NY 10016, USA
| | - Zina Chepurny
- Department of Physiology and Neuroscience, New York University School of MedicineNew York, NY 10016, USA
| | - Wen-hong Li
- Departments of Cell Biology and of Biochemistry, University of Texas Southwestern Medical Center5323 Harry Hines Blvd, Dallas, TX 75390-9039, USA
| | - Mark Harbeck
- Department of Medicine, Mc1027, amb m172, University of Chicago5841 South Maryland Avenue, Chicago, IL 60637
| | - Michael W Roe
- Department of Medicine, Mc1027, amb m172, University of Chicago5841 South Maryland Avenue, Chicago, IL 60637
| | - George G Holz
- Department of Physiology and Neuroscience, New York University School of MedicineNew York, NY 10016, USA
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Affiliation(s)
- Kevin J. Acheson
- Nutrition and Health Department, Nestlé Research Center, Lausanne, Switzerland
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Dyachok O, Tufveson G, Gylfe E. Ca2+-induced Ca2+ release by activation of inositol 1,4,5-trisphosphate receptors in primary pancreatic beta-cells. Cell Calcium 2004; 36:1-9. [PMID: 15126051 DOI: 10.1016/j.ceca.2003.11.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2003] [Revised: 10/15/2003] [Accepted: 11/01/2003] [Indexed: 10/26/2022]
Abstract
The effect of sarcoendoplasmic reticulum Ca(2+)-ATPase (SERCA) inhibition on the cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) was studied in primary insulin-releasing pancreatic beta-cells isolated from mice, rats and human subjects as well as in clonal rat insulinoma INS-1 cells. In Ca(2+)-deficient medium the individual primary beta-cells reacted to the SERCA inhibitor cyclopiazonic acid (CPA) with a slow rise of [Ca(2+)](i) followed by an explosive transient elevation. The [Ca(2+)](i) transients were preferentially observed at low intracellular concentrations of the Ca(2+) indicator fura-2 and were unaffected by pre-treatment with 100 microM ryanodine. Whereas 20mM caffeine had no effect on basal [Ca(2+)](i) or the slow rise in response to CPA, it completely prevented the CPA-induced [Ca(2+)](i) transients as well as inositol 1,4,5-trisphosphate-mediated [Ca(2+)](i) transients in response to carbachol. In striking contrast to the primary beta-cells, caffeine readily mobilized intracellular Ca(2+) in INS-1 cells under identical conditions, and such mobilization was prevented by ryanodine pre-treatment. The results indicate that leakage of Ca(2+) from the endoplasmic reticulum after SERCA inhibition is feedback-accelerated by Ca(2+)-induced Ca(2+) release (CICR). In primary pancreatic beta-cells this CICR is due to activation of inositol 1,4,5-trisphosphate receptors. CICR by ryanodine receptor activation may be restricted to clonal beta-cells.
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Affiliation(s)
- Oleg Dyachok
- Department of Surgical Sciences, Division of Transplantation Surgery, University Hospital, Uppsala, Sweden
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van Dam RM, Dekker JM, Nijpels G, Stehouwer CDA, Bouter LM, Heine RJ. Coffee consumption and incidence of impaired fasting glucose, impaired glucose tolerance, and type 2 diabetes: the Hoorn Study. Diabetologia 2004; 47:2152-9. [PMID: 15662556 DOI: 10.1007/s00125-004-1573-6] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/13/2004] [Accepted: 08/05/2004] [Indexed: 10/26/2022]
Abstract
AIMS/HYPOTHESIS Coffee contains several substances that may affect glucose metabolism. The aim of this study was to evaluate the relationship between habitual coffee consumption and the incidence of IFG, IGT and type 2 diabetes. METHODS We used cross-sectional and prospective data from the population-based Hoorn Study, which included Dutch men and women aged 50-74 years. An OGTT was performed at baseline and after a mean follow-up period of 6.4 years. Associations were adjusted for potential confounders including BMI, cigarette smoking, physical activity, alcohol consumption and dietary factors. RESULTS At baseline, a 5 cup per day higher coffee consumption was significantly associated with lower fasting insulin concentrations (-5.6%, 95% CI -9.3 to -1.6%) and 2-h glucose concentrations (-8.8%, 95% CI -11.8 to -5.6%), but was not associated with lower fasting glucose concentrations (-0.8%, 95% CI -2.1 to 0.6%). In the prospective analyses, the odds ratio (OR) for IGT was 0.59 (95% CI 0.36-0.97) for 3-4 cups per day, 0.46 (95% CI 0.26-0.81) for 5-6 cups per day, and 0.37 (95% CI 0.16-0.84) for 7 or more cups per day, as compared with the corresponding values for the consumption of 2 or fewer cups of coffee per day (p=0.001 for trend). Higher coffee consumption also tended to be associated with a lower incidence of type 2 diabetes (OR 0.69, CI 0.31-1.51 for >/=7 vs </=2 cups per day, p=0.09 for trend), but was not associated with the incidence of IFG (OR 1.35, CI 0.80-2.27 for >/=7 vs </=2 cups per day, p=0.49 for trend). CONCLUSIONS/INTERPRETATION Our findings indicate that habitual coffee consumption can reduce the risk of IGT, and affects post-load rather than fasting glucose metabolism.
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Affiliation(s)
- R M van Dam
- Department of Nutrition and Health, Faculty of Earth and Life Sciences, Vrije University Amsterdam, de Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands.
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van Dam RM, Pasman WJ, Verhoef P. Effects of coffee consumption on fasting blood glucose and insulin concentrations: randomized controlled trials in healthy volunteers. Diabetes Care 2004; 27:2990-2. [PMID: 15562223 DOI: 10.2337/diacare.27.12.2990] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- Rob M van Dam
- Department of Nutrition and Health, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, de Boelelaan 1085, 1081 HV Amsterdam, Netherlands.
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Gustafsson AJ, Ingelman-Sundberg H, Dzabic M, Awasum J, Nguyen KH, Ostenson CG, Pierro C, Tedeschi P, Woolcott O, Chiounan S, Lund PE, Larsson O, Islam MS. Ryanodine receptor‐operated activation of TRP‐like channels can trigger critical Ca2+signaling events in pancreatic β‐cells. FASEB J 2004; 19:301-3. [PMID: 15572434 DOI: 10.1096/fj.04-2621fje] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
There is little information available concerning the link between the ryanodine (RY) receptors and the downstream Ca(2+) signaling events in beta-cells. In fura-2 loaded INS-1E cells, activation of RY receptors by 9-methyl 5,7-dibromoeudistomin D (MBED) caused a rapid rise of [Ca(2+)]i followed by a plateau and repetitive [Ca(2+)]i spikes on the plateau. The [Ca(2+)]i plateau was abolished by omission of extracellular Ca(2+) and by SKF 96365. In the presence of SKF 96365, MBED produced a transient increase of [Ca(2+)]i, which was abolished by thapsigargin. Activation of RY receptors caused Ca(2+) entry even when the ER Ca(2+) pool was depleted by thapsigargin. The [Ca(2+)]i plateau was not inhibited by nimodipine or ruthenium red, but was inhibited by membrane depolarization, La(3+), Gd(3+), niflumic acid, and 2-aminoethoxydiphenyl borate, agents that inhibit the transient receptor potential channels. The [Ca(2+)]i spikes were inhibited by nimodipine and ryanodine, indicating that they were due to Ca(2+) influx through the voltage-gated Ca(2+) channels and Ca(2+)-induced Ca(2+) release (CICR). Activation of RY receptors depolarized membrane potential as measured by patch clamp. Thus, activation of RY receptors leads to coherent changes in Ca(2+) signaling, which includes activation of TRP-like channels, membrane depolarization, activation of the voltage-gated Ca(2+) channels and CICR.
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Affiliation(s)
- Amanda Jabin Gustafsson
- Department of Medicine, Karolinska Inst., Stockholm Söder Hospital, Stockholm 118 83, Sweden.
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Squires PE, Hills CE, Rogers GJ, Garland P, Farley SR, Morgan NG. The putative imidazoline receptor agonist, harmane, promotes intracellular calcium mobilisation in pancreatic β-cells. Eur J Pharmacol 2004; 501:31-9. [PMID: 15464060 DOI: 10.1016/j.ejphar.2004.08.018] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2004] [Revised: 08/04/2004] [Accepted: 08/09/2004] [Indexed: 10/26/2022]
Abstract
beta-Carbolines (including harmane and pinoline) stimulate insulin secretion by a mechanism that may involve interaction with imidazoline I(3)-receptors but which also appears to be mediated by actions that are additional to imidazoline receptor agonism. Using the MIN6 beta-cell line, we now show that both the imidazoline I(3)-receptor agonist, efaroxan, and the beta-carboline, harmane, directly elevate cytosolic Ca(2+) and increase insulin secretion but that these responses display different characteristics. In the case of efaroxan, the increase in cytosolic Ca(2+) was readily reversible, whereas, with harmane, the effect persisted beyond removal of the agonist and resulted in the development of a repetitive train of Ca(2+)-oscillations whose frequency, but not amplitude, was concentration-dependent. Initiation of the Ca(2+)-oscillations by harmane was independent of extracellular calcium but was sensitive to both dantrolene and high levels (20 mM) of caffeine, suggesting the involvement of ryanodine receptor-gated Ca(2+)-release. The expression of ryanodine receptor-1 and ryanodine receptor-2 mRNA in MIN6 cells was confirmed using reverse transcription-polymerase chain reaction (RT-PCR) and, since low concentrations of caffeine (1 mM) or thimerosal (10 microM) stimulated increases in [Ca(2+)](i), we conclude that ryanodine receptors are functional in these cells. Furthermore, the increase in insulin secretion induced by harmane was attenuated by dantrolene, consistent with the involvement of ryanodine receptors in mediating this response. By contrast, the smaller insulin secretory response to efaroxan was unaffected by dantrolene. Harmane-evoked changes in cytosolic Ca(2+) were maintained by nifedipine-sensitive Ca(2+)-influx, suggesting the involvement of L-type voltage-gated Ca(2+)-channels. Taken together, these data imply that harmane may interact with ryanodine receptors to generate sustained Ca(2+)-oscillations in pancreatic beta-cells and that this effect contributes to the insulin secretory response.
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Affiliation(s)
- Paul E Squires
- Molecular Physiology, Biomedical Research Institute, Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK
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Robinson LE, Savani S, Battram DS, McLaren DH, Sathasivam P, Graham TE. Caffeine ingestion before an oral glucose tolerance test impairs blood glucose management in men with type 2 diabetes. J Nutr 2004; 134:2528-33. [PMID: 15465742 DOI: 10.1093/jn/134.10.2528] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Caffeine ingestion negatively affects insulin sensitivity during an oral glucose tolerance test (OGTT) in lean and obese men, but this has not been studied in individuals with type 2 diabetes. We examined the effects of caffeine ingestion on insulin and glucose homeostasis in obese men with type 2 diabetes. Men (n = 12) with type 2 diabetes (age = 49 +/- 2 y, BMI = 32 +/- 1 kg/m(2)) underwent 2 trials, 1 wk apart, in a randomized, double-blind design. Each trial was conducted after withdrawal from caffeine, alcohol, exercise, and oral hypoglycemic agents for 48 h and an overnight fast. Subjects randomly ingested caffeine (5 mg/kg body weight) or placebo capsules and 1 h later began a 3 h 75 g OGTT. Caffeine increased (P < 0.05) serum insulin, proinsulin, and C-peptide concentrations during the OGTT relative to placebo. Insulin area under the curve was 25% greater (P < 0.05) after caffeine than after placebo ingestion. Despite this, blood glucose concentration was also increased (P < 0.01) in the caffeine trial. After caffeine ingestion, blood glucose remained elevated (P < 0.01) at 3 h postglucose load (8.9 +/- 0.7 mmol/L) compared with baseline (6.7 +/- 0.4 mmol/L). The insulin sensitivity index was lower (14%, P = 0.02) after caffeine than after placebo ingestion. Overall, despite elevated and prolonged proinsulin, C-peptide, and insulin responses after caffeine ingestion, blood glucose was also increased, suggesting an acute caffeine-induced impairment in blood glucose management in men with type 2 diabetes.
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Affiliation(s)
- Lindsay E Robinson
- Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, ON, Canada.
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Rudolf R, Mongillo M, Magalhães PJ, Pozzan T. In vivo monitoring of Ca(2+) uptake into mitochondria of mouse skeletal muscle during contraction. J Cell Biol 2004; 166:527-36. [PMID: 15314066 PMCID: PMC2172216 DOI: 10.1083/jcb.200403102] [Citation(s) in RCA: 168] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2004] [Accepted: 07/01/2004] [Indexed: 12/04/2022] Open
Abstract
Although the importance of mitochondria in patho-physiology has become increasingly evident, it remains unclear whether these organelles play a role in Ca(2+) handling by skeletal muscle. This undefined situation is mainly due to technical limitations in measuring Ca(2+) transients reliably during the contraction-relaxation cycle. Using two-photon microscopy and genetically expressed "cameleon" Ca(2+) sensors, we developed a robust system that enables the measurement of both cytoplasmic and mitochondrial Ca(2+) transients in vivo. We show here for the first time that, in vivo and under highly physiological conditions, mitochondria in mammalian skeletal muscle take up Ca(2+) during contraction induced by motor nerve stimulation and rapidly release it during relaxation. The mitochondrial Ca(2+) increase is delayed by a few milliseconds compared with the cytosolic Ca(2+) rise and occurs both during a single twitch and upon tetanic contraction.
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Affiliation(s)
- Rüdiger Rudolf
- Department of Biomedical Sciences, Institute of Neurosciences, University of Padua, Viale G. Colombo 3, I-35121 Padua, Italy
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Dyachok O, Gylfe E. Ca(2+)-induced Ca(2+) release via inositol 1,4,5-trisphosphate receptors is amplified by protein kinase A and triggers exocytosis in pancreatic beta-cells. J Biol Chem 2004; 279:45455-61. [PMID: 15316011 DOI: 10.1074/jbc.m407673200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hormones, such as glucagon and glucagon-like peptide-1, potently amplify nutrient stimulated insulin secretion by raising cAMP. We have studied how cAMP affects Ca(2+)-induced Ca(2+) release (CICR) in pancreatic beta-cells from mice and rats and the role of CICR in secretion. CICR was observed as pronounced Ca(2+) spikes on top of glucose- or depolarization-dependent rise of the cytoplasmic Ca(2+) concentration ([Ca(2+)](i)). cAMP-elevating agents strongly promoted CICR. This effect involved sensitization of the receptors underlying CICR, because many cells exhibited the characteristic Ca(2+) spiking at low or even in the absence of depolarization-dependent elevation of [Ca(2+)](i). The cAMP effect was mimicked by a specific activator of protein kinase A in cells unresponsive to activators of cAMP-regulated guanine nucleotide exchange factor. Ryanodine pretreatment, which abolishes CICR mediated by ryanodine receptors, did not prevent CICR. Moreover, a high concentration of caffeine, known to activate ryanodine receptors independently of Ca(2+), failed to mobilize intracellular Ca(2+). On the contrary, a high caffeine concentration abolished CICR by interfering with inositol 1,4,5-trisphosphate receptors (IP(3)Rs). Therefore, the cell-permeable IP(3)R antagonist 2-aminoethoxydiphenyl borate blocked the cAMP-promoted CICR. Individual CICR events in pancreatic beta-cells were followed by [Ca(2+)](i) spikes in neighboring human erythroleukemia cells, used to report secretory events in the beta-cells. The results indicate that protein kinase A-mediated promotion of CICR via IP(3)Rs is part of the mechanism by which cAMP amplifies insulin release.
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Affiliation(s)
- Oleg Dyachok
- Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
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Petrie HJ, Chown SE, Belfie LM, Duncan AM, McLaren DH, Conquer JA, Graham TE. Caffeine ingestion increases the insulin response to an oral-glucose-tolerance test in obese men before and after weight loss. Am J Clin Nutr 2004; 80:22-8. [PMID: 15213023 DOI: 10.1093/ajcn/80.1.22] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND Caffeine ingestion decreases the insulin sensitivity index (ISI) for an oral-glucose-tolerance test (OGTT) and decreases insulin-induced glucose disposal in lean male subjects during a hyperinsulinemic clamp. OBJECTIVE We examined the effects of caffeine ingestion on insulin and glucose homeostasis in obese men before and after a nutrition and exercise intervention. DESIGN Nine sedentary, obese [body mass index (in kg/m(2)): 34.0 +/- 1.0] men who had refrained from exercise and caffeine ingestion for 48 h underwent 2 oral-glucose-tolerance tests (OGTTs). The subjects randomly received caffeine (5 mg/kg) or placebo 1 h before each OGTT. After a 12-wk nutrition and exercise intervention, during which time the subjects avoided dietary caffeine, the OGTTs were repeated. RESULTS The intervention resulted in decreases (P < or = 0.05) in body weight (8.5 +/- 1.5 kg), percentage body fat (2.8 +/- 0.7%), and fasting glucose, insulin, and proinsulin concentrations and increases in the ISI for the placebo OGTT (P < or = 0.05). Caffeine caused a greater (P < or = 0.05) OGTT insulin response and a lower (P < or = 0.05) ISI both before and after weight loss. The proinsulin-insulin ratio indicated that neither weight loss nor caffeine affected the nature of the beta cell secretion of insulin. CONCLUSIONS A nutrition and exercise intervention improved, whereas caffeine ingestion impaired, insulin-glucose homeostasis in obese men. The results are consistent with previous findings that caffeine ingestion contributes to insulin resistance.
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Affiliation(s)
- Heather J Petrie
- Department of Human Biology and Nutritional Sciences, University of Guelph, Ontario, Canada
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Liu G, Hilliard N, Hockerman GH. Cav1.3 Is Preferentially Coupled to Glucose-Induced [Ca2+]iOscillations in the Pancreatic β Cell Line INS-1. Mol Pharmacol 2004; 65:1269-77. [PMID: 15102955 DOI: 10.1124/mol.65.5.1269] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The link between Ca(2+) influx through the L-type calcium channels Ca(v)1.2 or Ca(v)1.3 and glucose- or KCl-induced [Ca(2+)](i) mobilization in INS-1 cells was assessed using the calcium indicator indo-1. Cells responded to 18 mM glucose or 50 mM KCl stimulation with different patterns in [Ca(2+)](i) increases, although both were inhibited by 10 microM nifedipine. Although KCl elicited a prolonged elevation in [Ca(2+)](i), glucose triggered oscillations in [Ca(2+)](i.) Ca(v)1.2/dihydropyridine-insensitive (DHPi) cells and Ca(v)1.3/DHPi cells, and stable INS-1 cell lines expressing either DHP-insensitive Ca(v)1.2 or Ca(v)1.3 channels showed normal responses to glucose. However, in 10 microM nifedipine, only Ca(v)1.3/DHPi cells maintained glucose-induced [Ca(2+)](i) oscillation. In contrast, both cell lines exhibited DHP-resistant [Ca(2+)](i) increases in response to KCl. The percentage of cells responding to glucose was not significantly decreased by nifedipine in Ca(v)1.3/DHPi cells but was greatly reduced in Ca(v)1.2/DHPi cells. In 10 microM nifedipine, KCl-elicited [Ca(2+)](i) elevation was retained in both Ca(v)1.2/DHPi and Ca(v)1.3/DHPi cells. In INS-1 cells expressing the intracellular II-III loop of Ca(v)1.3, glucose failed to elicit [Ca(2+)](i) changes, whereas INS-1 cells expressing the Ca(v)1.2 II-III loop responded to glucose with normal [Ca(2+)](i) oscillation. INS-1 cells expressing Ca(v)1.2/DHPi containing the II-III loop of Ca(v)1.3 demonstrated a nifedipine-resistant slow increase in [Ca(2+)](i) and nifedipine-resistant insulin secretion in response to glucose that was partially inhibited by diltiazem. Thus, whereas the II-III loop of Ca(v)1.3 may be involved in coupling Ca(2+) influx to insulin secretion, distinct structural domains are required to mediate the preferential coupling of Ca(v)1.3 to glucose-induced [Ca(2+)](i) oscillation.
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Affiliation(s)
- Guohong Liu
- Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmacal Sciences, Purdue University, West Lafayette, Indiana, USA
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Holz GG. Epac: A new cAMP-binding protein in support of glucagon-like peptide-1 receptor-mediated signal transduction in the pancreatic beta-cell. Diabetes 2004; 53:5-13. [PMID: 14693691 PMCID: PMC3012130 DOI: 10.2337/diabetes.53.1.5] [Citation(s) in RCA: 274] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Recently published studies of islet cell function reveal unexpected features of glucagon-like peptide-1 (GLP-1) receptor-mediated signal transduction in the pancreatic beta-cell. Although GLP-1 is established to be a cAMP-elevating agent, these studies demonstrate that protein kinase A (PKA) is not the only cAMP-binding protein by which GLP-1 acts. Instead, an alternative cAMP signaling mechanism has been described, one in which GLP-1 activates cAMP-binding proteins designated as cAMP-regulated guanine nucleotide exchange factors (cAMPGEFs, also known as Epac). Two variants of Epac (Epac1 and Epac2) are expressed in beta-cells, and downregulation of Epac function diminishes stimulatory effects of GLP-1 on beta-cell Ca(2+) signaling and insulin secretion. Of particular note are new reports demonstrating that Epac couples beta-cell cAMP production to the stimulation of fast Ca(2+)-dependent exocytosis. It is also reported that Epac mediates the cAMP-dependent mobilization of Ca(2+) from intracellular Ca(2+) stores. This is a process of Ca(2+)-induced Ca(2+) release (CICR), and it generates an increase of [Ca(2+)](i) that may serve as a direct stimulus for mitochondrial ATP production and secretory granule exocytosis. This article summarizes new findings concerning GLP-1 receptor-mediated signal transduction and seeks to define the relative importance of Epac and PKA to beta-cell stimulus-secretion coupling.
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Affiliation(s)
- George G Holz
- Department of Physiology and Neuroscience, New York University School of Medicine, New York, New York 10016, USA.
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Graves TK, Hinkle PM. Ca(2+)-induced Ca(2+) release in the pancreatic beta-cell: direct evidence of endoplasmic reticulum Ca(2+) release. Endocrinology 2003; 144:3565-74. [PMID: 12865339 DOI: 10.1210/en.2002-0104] [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: 11/19/2022]
Abstract
The role of the Ca(2+)-induced Ca(2+) release channel (ryanodine receptor) in MIN6 pancreatic beta-cells was investigated. An endoplasmic reticulum (ER)-targeted "cameleon" was used to report lumenal free Ca(2+). Depolarization of MIN6 cells with KCl led to release of Ca(2+) from the ER. This ER Ca(2+) release was mimicked by treatment with the ryanodine receptor agonists caffeine and 4-chloro-m-cresol, reversed by voltage-gated Ca(2+) channel antagonists and blocked by treatment with antagonistic concentrations of ryanodine. The depolarization-induced rise in cytoplasmic Ca(2+) was also inhibited by ryanodine, which did not alter voltage-gated Ca(2+) channel activation. Both ER and cytoplasmic Ca(2+) changes induced by depolarization occurred in a dose-dependent manner. Glucose caused a delayed rise in cytoplasmic Ca(2+) but no detectable change in ER Ca(2+). Carbamyl choline caused ER Ca(2+) release, a response that was not altered by ryanodine. Taken together, these results provide strong evidence that Ca(2+)-induced Ca(2+) release augments cytoplasmic Ca(2+) signals in pancreatic beta-cells.
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Affiliation(s)
- Thomas K Graves
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York 14642, USA
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Mitchell KJ, Lai FA, Rutter GA. Ryanodine receptor type I and nicotinic acid adenine dinucleotide phosphate receptors mediate Ca2+ release from insulin-containing vesicles in living pancreatic beta-cells (MIN6). J Biol Chem 2003; 278:11057-64. [PMID: 12538591 DOI: 10.1074/jbc.m210257200] [Citation(s) in RCA: 146] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have demonstrated recently (Mitchell, K. J., Pinton, P., Varadi, A., Tacchetti, C., Ainscow, E. K., Pozzan, T., Rizzuto, R., and Rutter, G. A. (2001) J. Cell Biol. 155, 41-51) that ryanodine receptors (RyR) are present on insulin-containing secretory vesicles. Here we show that pancreatic islets and derived beta-cell lines express type I and II, but not type III, RyRs. Purified by subcellular fractionation and membrane immuno-isolation, dense core secretory vesicles were found to possess a similar level of type I RyR immunoreactivity as Golgi/endoplasmic reticulum (ER) membranes but substantially less RyR II than the latter. Monitored in cells expressing appropriately targeted aequorins, dantrolene, an inhibitor of RyR I channels, elevated free Ca(2+) concentrations in the secretory vesicle compartment from 40.1 +/- 6.7 to 90.4 +/- 14.8 microm (n = 4, p < 0.01), while having no effect on ER Ca(2+) concentrations. Furthermore, nicotinic acid adenine dinucleotide phosphate (NAADP), a novel Ca(2+)-mobilizing agent, decreased dense core secretory vesicle but not ER free Ca(2+) concentrations in permeabilized MIN6 beta-cells, and flash photolysis of caged NAADP released Ca(2+) from a thapsigargin-insensitive Ca(2+) store in single MIN6 cells. Because dantrolene strongly inhibited glucose-stimulated insulin secretion (from 3.07 +/- 0.51-fold stimulation to no significant glucose effect; n = 3, p < 0.01), we conclude that RyR I-mediated Ca(2+)-induced Ca(2+) release from secretory vesicles, possibly potentiated by NAADP, is essential for the activation of insulin secretion.
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Affiliation(s)
- Kathryn J Mitchell
- Henry Wellcome Laboratories of Integrated Cell Signaling and Department of Biochemistry, School of Medical Sciences, University Walk, University of Bristol, Bristol BS8 1TD, United Kingdom
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