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Pohorec V, Križančić Bombek L, Skelin Klemen M, Dolenšek J, Stožer A. Glucose-Stimulated Calcium Dynamics in Beta Cells From Male C57BL/6J, C57BL/6N, and NMRI Mice: A Comparison of Activation, Activity, and Deactivation Properties in Tissue Slices. Front Endocrinol (Lausanne) 2022; 13:867663. [PMID: 35399951 PMCID: PMC8988149 DOI: 10.3389/fendo.2022.867663] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/04/2022] [Accepted: 02/23/2022] [Indexed: 11/13/2022] Open
Abstract
Although mice are a very instrumental model in islet beta cell research, possible phenotypic differences between strains and substrains are largely neglected in the scientific community. In this study, we show important phenotypic differences in beta cell responses to glucose between C57BL/6J, C57BL/6N, and NMRI mice, i.e., the three most commonly used strains. High-resolution multicellular confocal imaging of beta cells in acute pancreas tissue slices was used to measure and quantitatively compare the calcium dynamics in response to a wide range of glucose concentrations. Strain- and substrain-specific features were found in all three phases of beta cell responses to glucose: a shift in the dose-response curve characterizing the delay to activation and deactivation in response to stimulus onset and termination, respectively, and distinct concentration-encoding principles during the plateau phase in terms of frequency, duration, and active time changes with increasing glucose concentrations. Our results underline the significance of carefully choosing and reporting the strain to enable comparison and increase reproducibility, emphasize the importance of analyzing a number of different beta cell physiological parameters characterizing the response to glucose, and provide a valuable standard for future studies on beta cell calcium dynamics in health and disease in tissue slices.
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Affiliation(s)
- Viljem Pohorec
- 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
- Faculty of Natural Sciences and Mathematics, University of Maribor, Maribor, Slovenia
- *Correspondence: Andraž Stožer, ; Jurij Dolenšek,
| | - Andraž Stožer
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
- *Correspondence: Andraž Stožer, ; Jurij Dolenšek,
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2
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Iamshanova O, Mariot P, Lehen'kyi V, Prevarskaya N. Comparison of fluorescence probes for intracellular sodium imaging in prostate cancer cell lines. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2016; 45:765-777. [PMID: 27660079 PMCID: PMC5045488 DOI: 10.1007/s00249-016-1173-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Revised: 07/23/2016] [Accepted: 09/02/2016] [Indexed: 10/25/2022]
Abstract
Sodium (Na+) ions are known to regulate many signaling pathways involved in both physiological and pathological conditions. In particular, alterations in intracellular concentrations of Na+ and corresponding changes in membrane potential are known to be major actors of cancer progression to metastatic phenotype. Though the functionality of Na+ channels and the corresponding Na+ currents can be investigated using the patch-clamp technique, the latter is rather invasive and a technically difficult method to study intracellular Na+ transients compared to Na+ fluorescence imaging. Despite the fact that Na+ signaling is considered an important controller of cancer progression, only few data using Na+ imaging approaches are available so far, suggesting the persisting challenge within the scientific community. In this study, we describe in detail the approach for application of Na+ imaging technique to measure intracellular Na+ variations in human prostate cancer cells. Accordingly, we used three Na+-specific fluorescent dyes-Na+-binding benzofuran isophthalate (SBFI), CoroNa™ Green (Corona) and Asante NaTRIUM Green-2 (ANG-2). These dyes have been assessed for optimal loading conditions, dissociation constant and working range after different calibration methods, and intracellular Na+ sensitivity, in order to determine which probe can be considered as the most reliable to visualize Na+ fluctuations in vitro.
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Affiliation(s)
- Oksana Iamshanova
- Inserm U1003, Laboratory of Excellence, Ion Channels Science and Therapeutics, Equipe Labellisée par la Ligue Nationale Contre le Cancer, SIRIC ONCOLille, Université des Sciences et Technologies de Lille, 59656, Villeneuve d'Ascq, France
| | - Pascal Mariot
- Inserm U1003, Laboratory of Excellence, Ion Channels Science and Therapeutics, Equipe Labellisée par la Ligue Nationale Contre le Cancer, SIRIC ONCOLille, Université des Sciences et Technologies de Lille, 59656, Villeneuve d'Ascq, France
| | - V'yacheslav Lehen'kyi
- Inserm U1003, Laboratory of Excellence, Ion Channels Science and Therapeutics, Equipe Labellisée par la Ligue Nationale Contre le Cancer, SIRIC ONCOLille, Université des Sciences et Technologies de Lille, 59656, Villeneuve d'Ascq, France
| | - Natalia Prevarskaya
- Inserm U1003, Laboratory of Excellence, Ion Channels Science and Therapeutics, Equipe Labellisée par la Ligue Nationale Contre le Cancer, SIRIC ONCOLille, Université des Sciences et Technologies de Lille, 59656, Villeneuve d'Ascq, France.
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3
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Lorenzo DN, Healy JA, Hostettler J, Davis J, Yang J, Wang C, Hohmeier HE, Zhang M, Bennett V. Ankyrin-B metabolic syndrome combines age-dependent adiposity with pancreatic β cell insufficiency. J Clin Invest 2015; 125:3087-102. [PMID: 26168218 DOI: 10.1172/jci81317] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Accepted: 05/27/2015] [Indexed: 12/22/2022] Open
Abstract
Rare functional variants of ankyrin-B have been implicated in human disease, including hereditary cardiac arrhythmia and type 2 diabetes (T2D). Here, we developed murine models to evaluate the metabolic consequences of these alterations in vivo. Specifically, we generated knockin mice that express either the human ankyrin-B variant R1788W, which is present in 0.3% of North Americans of mixed European descent and is associated with T2D, or L1622I, which is present in 7.5% of African Americans. Young AnkbR1788W/R1788W mice displayed primary pancreatic β cell insufficiency that was characterized by reduced insulin secretion in response to muscarinic agonists, combined with increased peripheral glucose uptake and concomitantly increased plasma membrane localization of glucose transporter 4 (GLUT4) in skeletal muscle and adipocytes. In contrast, older AnkbR1788W/R1788W and AnkbL1622I/L1622I mice developed increased adiposity, a phenotype that was reproduced in cultured adipocytes, and insulin resistance. GLUT4 trafficking was altered in animals expressing mutant forms of ankyrin-B, and we propose that increased cell surface expression of GLUT4 in skeletal muscle and fatty tissue of AnkbR1788W/R1788W mice leads to the observed age-dependent adiposity. Together, our data suggest that ankyrin-B deficiency results in a metabolic syndrome that combines primary pancreatic β cell insufficiency with peripheral insulin resistance and is directly relevant to the nearly one million North Americans bearing the R1788W ankyrin-B variant.
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Hellman B, Grapengiesser E. Glucose-induced inhibition of insulin secretion. Acta Physiol (Oxf) 2014; 210:479-88. [PMID: 24354538 DOI: 10.1111/apha.12217] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2013] [Revised: 11/04/2013] [Accepted: 12/16/2013] [Indexed: 12/14/2022]
Abstract
Increase in glucose is known to elevate the concentration of cytoplasmic Ca(2+) ([Ca(2+) ]i ) in pancreatic β-cells and stimulate insulin secretion. However, rise of glucose can also lower [Ca(2+) ]i and inhibit insulin release. In the present review, we examine the mechanisms for this inhibition and highlight its importance for the healthy β-cell and the development of diabetes. It is possible to distinguish between 60 and 90 s of prompt inhibition and the late inhibition seen after the first-phase peak of insulin release. The introductory inhibition is characteristic of the healthy β-cell and mediated by sequestration of [Ca(2+) ]i in the endoplasmic reticulum. This inhibition is easily seen in studies of isolated islets but too brief to be detected in a conventional intravenous glucose tolerance test. Coupled to simultaneous rise of glucagon, the introductory suppression of insulin release is the starting point for the antiphase relation between the subsequent insulin and glucagon pulses. Another effect of the initial suppression is to increase the pool of readily releasable granules responsible for the first-phase release of insulin. The presence of late inhibition of insulin release is an indicator of β-cell dysfunction. Patients with type 2 diabetes often respond to intravenous bolus injection of glucose with 5-10 min of late suppression of circulating insulin.
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Affiliation(s)
- B. Hellman
- Department of Medical Cell Biology; University of Uppsala; Uppsala Sweden
| | - E. Grapengiesser
- Department of Medical Cell Biology; University of Uppsala; Uppsala Sweden
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5
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Healy JA, Nilsson KR, Hohmeier HE, Berglund J, Davis J, Hoffman J, Kohler M, Li LS, Berggren PO, Newgard CB, Bennett V. Cholinergic augmentation of insulin release requires ankyrin-B. Sci Signal 2010; 3:ra19. [PMID: 20234002 DOI: 10.1126/scisignal.2000771] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Parasympathetic stimulation of pancreatic islets augments glucose-stimulated insulin secretion by inducing inositol trisphosphate receptor (IP(3)R)-mediated calcium ion (Ca2+) release. Ankyrin-B binds to the IP(3)R and is enriched in pancreatic beta cells. We found that ankyrin-B-deficient islets displayed impaired potentiation of insulin secretion by the muscarinic agonist carbachol, blunted carbachol-mediated intracellular Ca2+ release, and reduced the abundance of IP3R. Ankyrin-B-haploinsufficient mice exhibited hyperglycemia after oral ingestion but not after intraperitoneal injection of glucose, consistent with impaired parasympathetic potentiation of glucose-stimulated insulin secretion. The R1788W mutation of ankyrin-B impaired its function in pancreatic islets and is associated with type 2 diabetes in Caucasians and Hispanics. Thus, defective glycemic regulation through loss of ankyrin-B-dependent stabilization of IP3R is a potential risk factor for type 2 diabetes.
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Affiliation(s)
- Jane A Healy
- 1Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA
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Zhang F, Dey D, Bränström R, Forsberg L, Lu M, Zhang Q, Sjöholm A. BLX-1002, a novel thiazolidinedione with no PPAR affinity, stimulates AMP-activated protein kinase activity, raises cytosolic Ca2+, and enhances glucose-stimulated insulin secretion in a PI3K-dependent manner. Am J Physiol Cell Physiol 2008; 296:C346-54. [PMID: 19052259 DOI: 10.1152/ajpcell.00444.2008] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
BLX-1002 is a novel small thiazolidinedione with no apparent affinity to peroxisome proliferator-activated receptors (PPAR) that has been shown to reduce glycemia in type 2 diabetes without adipogenic effects. Its precise mechanisms of action, however, remain elusive, and no studies have been done with respect to possible effects of BLX-1002 on pancreatic beta-cells. We have investigated the influence of the drug on beta-cell function in mouse islets in vitro. BLX-1002 enhanced insulin secretion stimulated by high, but not low or intermediate, glucose concentrations. BLX-1002 also augmented cytoplasmic free Ca2+ concentration ([Ca2+](i)) at high glucose, an effect that was abolished by pretreatment with the Ca2+-ATPase inhibitor thapsigargin. In contrast, BLX-1002 did not interfere with voltage-gated Ca2+ channel or ATP-sensitive K+ channel activities. In addition, cellular NAD(P)H stimulated by glucose was not affected by the drug. The stimulatory effect of BLX-1002 on insulin secretion at high glucose was completely abolished by treatment with the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin or LY-294002. Stimulation of the beta-cells with BLX-1002 also induced activation of AMP-activated protein kinase (AMPK) at high glucose. Our study suggests that BLX-1002 potentiates insulin secretion only at high glucose in beta-cells in a PI3K-dependent manner. This effect of BLX-1002 is associated with an increased [Ca2+](i) mediated through Ca2+ mobilization, and an enhanced activation of AMPK. The glucose-sensitive stimulatory impact of BLX-1002 on beta-cell function may translate into substantial clinical benefits of the drug in the management of type 2 diabetes, by avoidance of hypoglycemia.
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Affiliation(s)
- Fan Zhang
- Diabetes Research Center, Dept. of Internal Medicine, Karolinska Institutet, South Hospital, SE-11883 Stockholm, Sweden
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7
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Dekki N, Nilsson R, Norgren S, Rössner SM, Appelskog I, Marcus C, Simell O, Pugliese A, Alejandro R, Ricordi C, Berggren PO, Juntti-Berggren L. Type 1 diabetic serum interferes with pancreatic beta-cell Ca2+-handling. Biosci Rep 2008; 27:321-6. [PMID: 17597394 DOI: 10.1007/s10540-007-9055-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
The aim of this study was to clarify the frequency of patients with type 1 diabetes that have serum that increases pancreatic beta-cell cytoplasmic free Ca(2+) concentration, [Ca(2+)](i), and if such an effect is also present in serum from first-degree relatives. We also studied a possible link between the serum effect and ethnic background as well as presence of autoantibodies. Sera obtained from three different countries were investigated as follows: 82 Swedish Caucasians with newly diagnosed type 1 diabetes, 56 Americans with different duration of type 1 diabetes, 117 American first-degree relatives of type 1 diabetic patients with a mixed ethnic background and 31 Caucasian Finnish children with newly diagnosed type 1 diabetes. Changes in [Ca(2+)](i) , upon depolarization, were measured in beta-cells incubated overnight with sera from type 1 diabetic patients, first-degree relatives or healthy controls. Our data show that there is a group constituting approximately 30% of type 1 diabetic patients of different gender, age, ethnic background and duration of the disease, as well as first-degree relatives of type 1 diabetic patients, that have sera that interfere with pancreatic beta-cell Ca(2+)-handling. This effect on beta-cell [Ca(2+)](i) could not be correlated to the presence of autoantibodies. In a defined subgroup of patients with type 1 diabetes and first-degree relatives a defect Ca(2+)-handling may aggravate development of beta-cell destruction.
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Affiliation(s)
- N Dekki
- The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Karolinska University Hospital, L1, Stockholm, 171 76, Sweden
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8
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Zhang W, Lilja L, Mandic SA, Gromada J, Smidt K, Janson J, Takai Y, Bark C, Berggren PO, Meister B. Tomosyn is expressed in beta-cells and negatively regulates insulin exocytosis. Diabetes 2006; 55:574-81. [PMID: 16505218 DOI: 10.2337/diabetes.55.03.06.db05-0015] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Tomosyn, a syntaxin-binding protein, is capable of dissociating mammalian homolog of the Caenorhabditis elegans unc-18 gene from syntaxin and is involved in the regulation of exocytosis. We have investigated the expression, cellular localization, and functional role of tomosyn in pancreatic beta-cells. Western blotting revealed a 130-kDa protein corresponding to tomosyn in insulin-secreting beta-cell lines. RT-PCR amplification showed that b-, m-, and s-tomosyn isoform mRNAs are expressed in beta-cell lines and rat pancreatic islets. Immunohistochemistry revealed punctate tomosyn immunoreactivity in the cytoplasm of insulin-, glucagon-, pancreatic polypeptide-, and somatostatin-containing islet cells. Syntaxin 1 coimmunoprecipitated with tomosyn in extracts of insulin-secreting cells. Overexpression of m-tomosyn in mouse beta-cells significantly decreased exocytosis, whereas inhibition of tomosyn expression by small interfering RNA increased exocytosis. Hence, in the pancreatic beta-cell, tomosyn negatively regulates insulin exocytosis.
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Affiliation(s)
- Wei Zhang
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
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9
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Lilja L, Meister B, Berggren PO, Bark C. DARPP-32 and inhibitor-1 are expressed in pancreatic β-cells. Biochem Biophys Res Commun 2005; 329:673-7. [PMID: 15737638 DOI: 10.1016/j.bbrc.2005.02.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2004] [Indexed: 11/20/2022]
Abstract
Insulin secretion from pancreatic beta-cells has to be tightly regulated to ensure accurate glucose homeostasis. The capacity of beta-cells to respond to extracellular stimulation is determined by several signaling pathways. One important feature of these pathways is phosphorylation and subsequent dephosphorylation of a wide range of cellular substrates. Protein phosphatase 1 (PP1) is a major eukaryotic serine/threonine protein phosphatase that controls a multitude of physiological processes. We have investigated the expression and cellular distribution of two endogenous inhibitors of PP1 activity in beta-cells. RT-PCR, Western blotting, and immunohistochemistry showed that DARPP-32 and inhibitor-1 are present in insulin-secreting endocrine beta-cells. Subcellular fractionation of mouse islets revealed that both PP1 inhibitors predominantly localized to cytosol-enriched fractions. Inhibitor-1 was also present in fractions containing plasma membrane-associated proteins. These data indicate a potential role for DARPP-32 and inhibitor-1 in the regulation of PP1 activity in pancreatic beta-cell stimulus-secretion coupling.
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Affiliation(s)
- Lena Lilja
- The Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institutet, Karolinska University Hospital, SE-171 76 Stockholm, Sweden
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10
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Juntti-Berggren L, Refai E, Appelskog I, Andersson M, Imreh G, Dekki N, Uhles S, Yu L, Griffiths WJ, Zaitsev S, Leibiger I, Yang SN, Olivecrona G, Jörnvall H, Berggren PO. Apolipoprotein CIII promotes Ca2+-dependent beta cell death in type 1 diabetes. Proc Natl Acad Sci U S A 2004; 101:10090-4. [PMID: 15210953 PMCID: PMC454169 DOI: 10.1073/pnas.0403551101] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In type 1 diabetes (T1D), there is a specific destruction of the insulin secreting pancreatic beta cell. Although the exact molecular mechanisms underlying beta cell destruction are not known, sera from T1D patients have been shown to promote Ca(2+)-induced apoptosis. We now demonstrate that apolipoprotein CIII (apoCIII) is increased in serum from T1D patients and that this serum factor both induces increased cytoplasmic free intracellular Ca(2+) concentration ([Ca(2+)](i)) and beta cell death. The apoCIII-induced increase in [Ca(2+)](i) reflects an activation of the voltage-gated L-type Ca(2+) channel. Both the effects of T1D sera and apoCIII on the beta cell are abolished in the presence of antibody against apoCIII. Increased serum levels of apoCIII can thus account for the increase in beta cell [Ca(2+)](i) and thereby beta cell apoptosis associated with T1D.
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Affiliation(s)
- Lisa Juntti-Berggren
- Department of Molecular Medicine, Rolf Luft Center for Diabetes Research, Karolinska Institutet, SE-171 76 Stockholm, Sweden.
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11
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Kulkarni RN, Roper MG, Dahlgren G, Shih DQ, Kauri LM, Peters JL, Stoffel M, Kennedy RT. Islet secretory defect in insulin receptor substrate 1 null mice is linked with reduced calcium signaling and expression of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)-2b and -3. Diabetes 2004; 53:1517-25. [PMID: 15161756 DOI: 10.2337/diabetes.53.6.1517] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Mice with deletion of insulin receptor substrate (IRS)-1 (IRS-1 knockout [KO] mice) show mild insulin resistance and defective glucose-stimulated insulin secretion and reduced insulin synthesis. To further define the role of IRS-1 in islet function, we examined the insulin secretory defect in the knockouts using freshly isolated islets and primary beta-cells. IRS-1 KO beta-cells exhibited a significantly shorter increase in intracellular free Ca(2+) concentration ([Ca(2+)](i)) than controls when briefly stimulated with glucose or glyceraldehyde and when l-arginine was used to potentiate the stimulatory effect of glucose. These changes were paralleled by a lower number of exocytotic events in the KO beta-cells in response to the same secretagogues, indicating reduced insulin secretion. Furthermore, the normal oscillations in intracellular Ca(2+) and O(2) consumption after glucose stimulation were dampened in freshly isolated KO islets. Semiquantitative RT-PCR showed a dramatically reduced islet expression of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)-2b and -3 in the mutants. These data provide evidence that IRS-1 modulation of insulin secretion is associated with Ca(2+) signaling and expression of SERCA-2b and -3 genes in pancreatic islets and provides a direct link between insulin resistance and defective insulin secretion.
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Affiliation(s)
- Rohit N Kulkarni
- Rm. 602, Joslin Diabetes Center, One Joslin Pl., Boston MA 02215, USA.
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12
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Lilja L, Johansson JU, Gromada J, Mandic SA, Fried G, Berggren PO, Bark C. Cyclin-dependent kinase 5 associated with p39 promotes Munc18-1 phosphorylation and Ca(2+)-dependent exocytosis. J Biol Chem 2004; 279:29534-41. [PMID: 15123626 DOI: 10.1074/jbc.m312711200] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine/threonine protein kinase that requires association with a regulatory protein, p35 or p39, to form an active enzyme. Munc18-1 plays an essential role in membrane fusion, and its function is regulated by phosphorylation. We report here that both p35 and p39 were expressed in insulin-secreting beta-cells, where they exhibited individual subcellular distributions and associated with membranous organelles of different densities. Overexpression of Cdk5, p35, or p39 showed that Cdk5 and p39 augmented Ca(2+)-induced insulin exocytosis. Suppression of p39 and Cdk5, but not of p35, by antisense oligonucleotides selectively inhibited insulin exocytosis. Transient transfection of primary beta-cells with Munc18-1 templates mutated in potential Cdk5 or PKC phosphorylation sites, in combination with Cdk5 and the different Cdk5 activators, suggested that Cdk5/p39-promoted Ca(2+)-dependent insulin secretion from primary beta-cells by phosphorylating Munc18-1 at a biochemical step immediately prior to vesicle fusion.
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Affiliation(s)
- Lena Lilja
- Department of Molecular Medicine, Karolinska Institutet, Karolinska University Hospital, SE-171 76 Stockholm, Sweden
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13
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Köhler M, Zaitsev SV, Zaitseva II, Leibiger B, Leibiger IB, Turunen M, Kapelioukh IL, Bakkman L, Appelskog IB, de Monvel JB, Imreh G, Berggren PO. On-line monitoring of apoptosis in insulin-secreting cells. Diabetes 2003; 52:2943-50. [PMID: 14633855 DOI: 10.2337/diabetes.52.12.2943] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Apoptosis was monitored in intact insulin-producing cells both with microfluorometry and with two-photon laser scanning microscopy (TPLSM), using a fluorescent protein based on fluorescence resonance energy transfer (FRET). TPLSM offers three-dimensional spatial information that can be obtained relatively deep in tissues. This provides a potential for future in vivo studies of apoptosis. The cells expressed a fluorescent protein (C-DEVD-Y) consisting of two fluorophores, enhanced cyan fluorescent protein (ECFP) and enhanced yellow fluorescent protein (EYFP), linked by the amino acid sequence DEVD selectively cleaved by caspase-3-like proteases. FRET between ECFP and EYFP in C-DEVD-Y could therefore be monitored on-line as a sensor of caspase-3 activation. The relevance of using caspase-3 activation to indicate beta-cell apoptosis was demonstrated by inhibiting caspase-3-like proteases with Z-DEVD-fmk and thereby showing that caspase-3 activation was needed for high-glucose-and cytokine-induced apoptosis in the beta-cell and for staurosporine-induced apoptosis in RINm5F cells. In intact RINm5F cells expressing C-DEVD-Y and in MIN6 cells expressing the variant C-DEVD-Y2, FRET was lost at 155 +/- 23 min (n = 9) and 257 +/- 59 min (n = 4; mean +/- SE) after activation of apoptosis with staurosporine (6 micromol/l), showing that this method worked in insulin-producing cells.
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Affiliation(s)
- Martin Köhler
- Department of Molecular Medicine, Karolinska Institutet, Karolinska Hospital, Stockholm, Sweden.
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14
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Mendez CF, Leibiger IB, Leibiger B, Høy M, Gromada J, Berggren PO, Bertorello AM. Rapid association of protein kinase C-epsilon with insulin granules is essential for insulin exocytosis. J Biol Chem 2003; 278:44753-7. [PMID: 12941947 DOI: 10.1074/jbc.m308664200] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glucose-dependent exocytosis of insulin requires activation of protein kinase C (PKC). However, because of the great variety of isoforms and their ubiquitous distribution within the beta-cell, it is difficult to predict the importance of a particular isoform and its mode of action. Previous data revealed that two PKC isoforms (alpha and epsilon) translocate to membranes in response to glucose (Zaitzev, S. V., Efendic, S., Arkhammar, P., Bertorello, A. M., and Berggren, P. O. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 9712-9716). Using confocal microscopy, we have now established that in response to glucose, PKC-epsilon but not PKC-alpha associates with insulin granules and that green fluorescent protein-tagged PKC-epsilon changes its distribution within the cell periphery upon stimulation of beta-cells with glucose. Definite evidence of PKC-epsilon requirement during insulin granule exocytosis was obtained by using a dominant negative mutant of this isoform. The presence of this mutant abolished glucose-induced insulin secretion, whereas transient expression of the wild-type PKC-epsilon led to a significant increase in insulin exocytosis. These results suggest that association of PKC-epsilon with insulin granule membranes represents an important component of the secretory network because it is essential for insulin exocytosis in response to glucose.
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Affiliation(s)
- Carlos F Mendez
- Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institutet, Karolinska Hospital, SE-171 76 Stockholm, Sweden
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15
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Juntti-Berggren L, Webb DL, Arkhammar POG, Schultz V, Schweda EKH, Tornheim K, Berggren PO. Dihydroxyacetone-induced oscillations in cytoplasmic free Ca2+ and the ATP/ADP ratio in pancreatic beta-cells at substimulatory glucose. J Biol Chem 2003; 278:40710-6. [PMID: 12917415 DOI: 10.1074/jbc.m308248200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glucose stimulation of pancreatic beta-cells causes oscillatory influx of Ca2+, leading to pulsatile insulin secretion. We have proposed that this is due to oscillations of glycolysis and the ATP/ADP ratio, which modulate the activity of ATP-sensitive K+ channels. We show here that dihydroxyacetone, a secretagogue that feeds into glycolysis below the putative oscillator phosphofructokinase, could cause a single initial peak in cytoplasmic free Ca2+ ([Ca2+]i) but did not by itself cause repeated oscillations in [Ca2+]i in mouse pancreatic beta-cells. However, in the presence of a substimulatory concentration of glucose (4 mm), dihydroxyacetone induced [Ca2+]i oscillations. Furthermore, these oscillations correlated with oscillations in the ATP/ADP ratio, as seen previously with glucose stimulation. Insulin secretion in response to dihydroxyacetone was transient in the absence of glucose but was considerably enhanced and somewhat prolonged in the presence of a substimulatory concentration of glucose, in accordance with the enhanced [Ca2+]i response. These results are consistent with the hypothesized role of phosphofructokinase as the generator of the oscillations. Dihydroxyacetone may affect phosphofructokinase by raising the free concentration of fructose 1,6-bisphosphate to a critical level at which it activates the enzyme autocatalytically, thereby inducing the pulses of phosphofructokinase activity that cause the metabolic oscillations.
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Affiliation(s)
- Lisa Juntti-Berggren
- Department of Molecular Medicine, The Rolf Luft Center for Diabetes Research, Karolinska Institutet, Karolinska Hospital, S-171 76 Stockholm, Sweden
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16
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Olsen HL, Hoy M, Zhang W, Bertorello AM, Bokvist K, Capito K, Efanov AM, Meister B, Thams P, Yang SN, Rorsman P, Berggren PO, Gromada J. Phosphatidylinositol 4-kinase serves as a metabolic sensor and regulates priming of secretory granules in pancreatic beta cells. Proc Natl Acad Sci U S A 2003; 100:5187-92. [PMID: 12700357 PMCID: PMC154320 DOI: 10.1073/pnas.0931282100] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2002] [Accepted: 03/05/2003] [Indexed: 11/18/2022] Open
Abstract
Insulin secretion is controlled by the beta cell's metabolic state, and the ability of the secretory granules to undergo exocytosis increases during glucose stimulation in a membrane potential-independent fashion. Here, we demonstrate that exocytosis of insulin-containing secretory granules depends on phosphatidylinositol 4-kinase (PI 4-kinase) activity and that inhibition of this enzyme suppresses glucose-stimulated insulin secretion. Intracellular application of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P(2)] stimulated exocytosis by promoting the priming of secretory granules for release and increasing the number of granules residing in a readily releasable pool. Reducing the cytoplasmic ADP concentration in a way mimicking the effects of glucose stimulation activated PI 4-kinase and increased exocytosis whereas changes of the ATP concentration in the physiological range had little effect. The PI(4,5)P(2)-binding protein Ca(2+)-dependent activator protein for secretion (CAPS) is present in beta cells, and neutralization of the protein abolished both Ca(2+)- and PI(4,5)P(2)-induced exocytosis. We conclude that ADP-induced changes in PI 4-kinase activity, via generation of PI(4,5)P(2), represents a metabolic sensor in the beta cell by virtue of its capacity to regulate the release competence of the secretory granules.
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Affiliation(s)
- Hervør L Olsen
- Islet Cell Physiology, Novo Nordisk AS, Novo Alle, DK-2880 Bagsvaerd, Denmark
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17
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Varadi A, Rutter GA. Dynamic imaging of endoplasmic reticulum Ca2+ concentration in insulin-secreting MIN6 Cells using recombinant targeted cameleons: roles of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)-2 and ryanodine receptors. Diabetes 2002; 51 Suppl 1:S190-201. [PMID: 11815480 DOI: 10.2337/diabetes.51.2007.s190] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The endoplasmic reticulum (ER) plays a pivotal role in the regulation of cytosolic Ca(2+) concentrations ([Ca(2+)](cyt)) and hence in insulin secretion from pancreatic beta-cells. However, the molecular mechanisms involved in both the uptake and release of Ca(2+) from the ER are only partially defined in these cells, and the presence and regulation of ER ryanodine receptors are a matter of particular controversy. To monitor Ca(2+) fluxes across the ER membrane in single live MIN6 beta-cells, we have imaged changes in the ER intralumenal free Ca(2+) concentration ([Ca(2+)](ER)) using ER-targeted cameleons. Resting [Ca(2+)](ER) (approximately 250 micromol/l) was markedly reduced after suppression (by approximately 40%) of the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)-2b but not the SERCA3 isoform by microinjection of antisense oligonucleotides, implicating SERCA2b as the principle ER Ca(2+)-ATPase in this cell type. Nutrient secretagogues that elevated [Ca(2+)](cyt) also increased [Ca(2+)](ER), an effect most marked at the cell periphery, whereas inositol 1,4,5-trisphosphate-generating agents caused a marked and homogenous lowering of [Ca(2+)](ER). Demonstrating the likely presence of ryanodine receptors (RyRs), caffeine and 4-chloro-3-ethylphenol both caused an almost complete emptying of ER Ca(2+) and marked increases in [Ca(2+)](cyt). Furthermore, photolysis of caged cyclic ADP ribose increased [Ca(2+)](cyt), and this effect was largely abolished by emptying ER/Golgi stores with thapsigargin. Expression of RyR protein in living MIN6, INS-1, and primary mouse beta-cells was also confirmed by the specific binding of cell-permeate BODIPY TR-X ryanodine. RyR channels are likely to play an important part in the regulation of intracellular free Ca(2+) changes in the beta-cell and thus in the regulation of insulin secretion.
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Affiliation(s)
- Aniko Varadi
- Department of Biochemistry, University of Bristol, Bristol, U.K
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18
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Gilon P, Henquin JC. Mechanisms and physiological significance of the cholinergic control of pancreatic beta-cell function. Endocr Rev 2001; 22:565-604. [PMID: 11588141 DOI: 10.1210/edrv.22.5.0440] [Citation(s) in RCA: 181] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Acetylcholine (ACh), the major parasympathetic neurotransmitter, is released by intrapancreatic nerve endings during the preabsorptive and absorptive phases of feeding. In beta-cells, ACh binds to muscarinic M(3) receptors and exerts complex effects, which culminate in an increase of glucose (nutrient)-induced insulin secretion. Activation of PLC generates diacylglycerol. Activation of PLA(2) produces arachidonic acid and lysophosphatidylcholine. These phospholipid-derived messengers, particularly diacylglycerol, activate PKC, thereby increasing the efficiency of free cytosolic Ca(2+) concentration ([Ca(2+)](c)) on exocytosis of insulin granules. IP3, also produced by PLC, causes a rapid elevation of [Ca(2+)](c) by mobilizing Ca(2+) from the endoplasmic reticulum; the resulting fall in Ca(2+) in the organelle produces a small capacitative Ca(2+) entry. ACh also depolarizes the plasma membrane of beta-cells by a Na(+)- dependent mechanism. When the plasma membrane is already depolarized by secretagogues such as glucose, this additional depolarization induces a sustained increase in [Ca(2+)](c). Surprisingly, ACh can also inhibit voltage-dependent Ca(2+) channels and stimulate Ca(2+) efflux when [Ca(2+)](c) is elevated. However, under physiological conditions, the net effect of ACh on [Ca(2+)](c) is always positive. The insulinotropic effect of ACh results from two mechanisms: one involves a rise in [Ca(2+)](c) and the other involves a marked, PKC-mediated increase in the efficiency of Ca(2+) on exocytosis. The paper also discusses the mechanisms explaining the glucose dependence of the effects of ACh on insulin release.
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Affiliation(s)
- P Gilon
- Unité d'Endocrinologie et Métabolisme, University of Louvain Faculty of Medicine, B-1200 Brussels, Belgium.
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19
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Kindmark H, Köhler M, Brown G, Bränström R, Larsson O, Berggren PO. Glucose-induced oscillations in cytoplasmic free Ca2+ concentration precede oscillations in mitochondrial membrane potential in the pancreatic beta-cell. J Biol Chem 2001; 276:34530-6. [PMID: 11445566 DOI: 10.1074/jbc.m102492200] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Using dual excitation and fixed emission fluorescence microscopy, we were able to measure changes in cytoplasmic free Ca(2+) concentration ([Ca(2+)](i)) and mitochondrial membrane potential simultaneously in the pancreatic beta-cell. The beta-cells were exposed to a combination of the Ca(2+) indicator fura-2/AM and the indicator of mitochondrial membrane potential, rhodamine 123 (Rh123). Using simultaneous measurements of mitochondrial membrane potential and [Ca(2+)](i) during glucose stimulation, it was possible to measure the time lag between the onset of mitochondrial hyperpolarization and changes in [Ca(2+)](i). Glucose-induced oscillations in [Ca(2+)](i) were followed by transient depolarizations of mitochondrial membrane potential. These results are compatible with a model in which nadirs in [Ca(2+)](i) oscillations are generated by a transient, Ca(2+)-induced inhibition of mitochondrial metabolism resulting in a temporary fall in the cytoplasmic ATP/ADP ratio, opening of plasma membrane K(ATP) channels, repolarization of the plasma membrane, and thus transient closure of voltage-gated L-type Ca(2+) channels.
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Affiliation(s)
- H Kindmark
- Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institutet, Karolinska Hospital, S-171 76 Stockholm, Sweden.
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20
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Lilja L, Yang SN, Webb DL, Juntti-Berggren L, Berggren PO, Bark C. Cyclin-dependent kinase 5 promotes insulin exocytosis. J Biol Chem 2001; 276:34199-205. [PMID: 11443123 DOI: 10.1074/jbc.m103776200] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cyclin-dependent kinase 5 (Cdk5) is widely expressed although kinase activity has been described preferentially in neuronal systems. Cdk5 has an impact on actin polymerization during neuronal migration and neurite outgrowth and deregulation of the kinase has been implicated in the promotion of neurodegeneration. Recently it was shown that Cdk5 modulates dopamine signaling in neurons by regulating DARPP-32 function. In addition, Cdk5 phosphorylates munc-18 and synapsin I, two essential components of the exocytotic machinery. We have shown by reverse transcriptase-polymerase chain reaction, immunocytochemistry, and Western blotting that Cdk5 is present in the insulin-secreting pancreatic beta-cell. Subcellular fractionation of isolated beta-cells revealed a glucose-induced translocation of membrane-bound Cdk5 protein to lower density fractions. Inhibition of Cdk5 with roscovitine reduced insulin secretion with approximately 35% compared with control after glucose stimulation and with approximately 65% after depolarization with glucose and KCl. Capacitance measurements performed on single beta-cells that expressed a dominant-negative Cdk5 mutant showed impaired exocytosis. The effect on exocytosis by Cdk5 appeared to be independent of changes in free cytoplasmic Ca(2+) concentration. Taken together these results show that Cdk5 is present in beta-cells and acts as a positive regulator of insulin exocytosis.
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Affiliation(s)
- L Lilja
- Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institutet, Karolinska Hospital, S-171 76 Stockholm, Sweden
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21
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Nakazaki M, Kakei M, Yaekura K, Koriyama N, Morimitsu S, Ichinari K, Yada T, Tei C. Diverse effects of hydrogen peroxide on cytosolic Ca2+ homeostasis in rat pancreatic beta-cells. Cell Struct Funct 2000; 25:187-93. [PMID: 10984102 DOI: 10.1247/csf.25.187] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Oxygen-free radicals are thought to be a major cause of beta-cell dysfunction in diabetic animals induced by alloxan or streptozotocin. We evaluated the effect of H2O2 on cytosolic Ca2+ concentration ([Ca2+]i) and the activity of ATP-sensitive potassium (K+ATP) channels in isolated rat pancreatic beta-cells using microfluorometry and patch clamp techniques. Exposure to 0.1 mM H2O2 in the presence of 2.8 mM glucose increased [Ca2+]i from 114.3+/-15.4 nM to 531.1+/-71.9 nM (n=6) and also increased frequency of K+ATP channel openings. The intensity of NAD(P)H autofluorescence was conversely reduced, suggesting that H2O2 inhibited the cellular metabolism. These three types of cellular parameters were reversed to the control level on washout of H2O2, followed by a transient increase in [Ca2+]i, the transient inhibition of K+ATP channels associated with action currents and increase of the NAD(P)H intensity with an overshoot. In the absence of external Ca2+, 0.1 mM H2O2 increased [Ca2+]i from 88.8+/-7.2 nM to 134.6+/-8.3 nM. Magnitude of [Ca2+]i increase induced by 0.1 mM H2O2 was decreased after treatment of cells with 0.5 mM thapsigargin, an inhibitor of endoplasmic reticulum Ca2+ pump (45.8+/-4.9 nM vs 15.0+/-4.8 nM). Small increase in [Ca2+]i in response to an increase of external Ca2+ from zero to 2 mM was further facilitated by 0.1 mM H2O2 (330.5+/-122.7 nM). We concluded that H2O2 not only activates K+ATP channels in association with metabolic inhibition, but also increases partly the Ca2+ permeability of the thapsigargin-sensitive intracellular stores and of the plasma membrane in pancreatic beta-cells.
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Affiliation(s)
- M Nakazaki
- First Department of Internal Medicine, Faculty of Medicine, Kagoshima University, Japan
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22
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Bosqueiro JR, Carneiro EM, Bordin S, Boschero AC. Tetracaine stimulates insulin secretion through the mobilization of Ca 2+from thapsigargin- and IP 3-insensitive Ca 2+reservoir in pancreatic β-cells. Can J Physiol Pharmacol 2000. [DOI: 10.1139/y00-010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The effect of tetracaine on45Ca efflux, cytoplasmic Ca2+concentration [Ca2+]i, and insulin secretion in isolated pancreatic islets and β-cells was studied. In the absence of external Ca2+, tetracaine (0.1-2.0 mM) increased the45Ca efflux from isolated islets in a dose-dependant manner. Tetracaine did not affect the increase in45Ca efflux caused by 50 mM K+or by the association of carbachol (0.2 mM) and 50 mM K+. Tetracaine permanently increased the [Ca2+]iin isolated β-cells in Ca2+-free medium enriched with 2.8 mM glucose and 25 µM D-600 (methoxiverapamil). This effect was also observed in the presence of 10 mM caffeine or 1 µM thapsigargin. In the presence of 16.7 mM glucose, tetracaine transiently increased the insulin secretion from islets perfused in the absence and presence of external Ca2+. These data indicate that tetracaine mobilises Ca2+from a thapsigargin-insensitive store and stimulates insulin secretion in the absence of extracellular Ca2+. The increase in45Ca efflux caused by high concentrations of K+and by carbachol indicates that tetracaine did not interfere with a cation or inositol triphosphate sensitive Ca2+pool in β-cells.
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23
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Tengholm A, Hellman B, Gylfe E. Glucose regulation of free Ca(2+) in the endoplasmic reticulum of mouse pancreatic beta cells. J Biol Chem 1999; 274:36883-90. [PMID: 10601240 DOI: 10.1074/jbc.274.52.36883] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Free Ca(2+) was measured in organelles of individual mouse pancreatic beta cells loaded with the low affinity indicator furaptra. After removal of cytoplasmic indicator by controlled digitonin permeabilization the organelle Ca(2+) was located essentially in the endoplasmic reticulum (ER), >90% being sensitive to inhibition of sarco(endo)plasmic reticulum Ca(2+)-ATPases. The Ca(2+) accumulation in the ER of intact beta cells depended in a hyperbolic fashion on the glucose concentration with half-maximal and maximal filling at 5.5 and >20 mM, respectively. Also elevation of cytoplasmic Ca(2+) by K(+) depolarization significantly enhanced the Ca(2+) accumulation. In permeabilized beta cells 1-3 mM ATP caused rapid Ca(2+) filling of the ER reaching almost 500 microM. At 50 nM, Ca(2+) ER became half-maximally filled at 45 microM ATP, whereas only 3.5 microM ATP was required at 200 nM Ca(2+). Inositol 1,4,5-trisphosphate induced a rapid release of about 65% of the ER Ca(2+), and its precursor phosphatidylinositol 4,5-bisphosphate was found to slowly mobilize 75% by another mechanism. It is concluded that glucose is an efficient stimulator of Ca(2+) uptake in the ER of pancreatic beta cells both by increasing ATP and cytoplasmic Ca(2+). Because physiological concentrations of cytoplasmic ATP are in the mM range, Ca(2+) sequestration can be anticipated to be modulated by factors reducing its ATP sensitivity.
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Affiliation(s)
- A Tengholm
- Department of Medical Cell Biology, Uppsala University, SE-751 23 Uppsala, Sweden
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24
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Owada S, Larsson O, Arkhammar P, Katz AI, Chibalin AV, Berggren PO, Bertorello AM. Glucose decreases Na+,K+-ATPase activity in pancreatic beta-cells. An effect mediated via Ca2+-independent phospholipase A2 and protein kinase C-dependent phosphorylation of the alpha-subunit. J Biol Chem 1999; 274:2000-8. [PMID: 9890957 DOI: 10.1074/jbc.274.4.2000] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the pancreatic beta-cell, glucose-induced membrane depolarization promotes opening of voltage-gated L-type Ca2+ channels, an increase in cytoplasmic free Ca2+ concentration ([Ca2+]i), and exocytosis of insulin. Inhibition of Na+,K+-ATPase activity by ouabain leads to beta-cell membrane depolarization and Ca2+ influx. Because glucose-induced beta-cell membrane depolarization cannot be attributed solely to closure of ATP-regulated K+ channels, we investigated whether glucose regulates other transport proteins, such as the Na+,K+-ATPase. Glucose inhibited Na+,K+-ATPase activity in single pancreatic islets and intact beta-cells. This effect was reversible and required glucose metabolism. The inhibitory action of glucose was blocked by pretreatment of the islets with a selective inhibitor of a Ca2+-independent phospholipase A2. Arachidonic acid, the hydrolytic product of this phospholipase A2, also inhibited Na+, K+-ATPase activity. This effect, like that of glucose, was blocked by nordihydroguaiaretic acid, a selective inhibitor of the lipooxygenase metabolic pathway, but not by inhibitors of the cyclooxygenase or cytochrome P450-monooxygenase pathways. The lipooxygenase product 12(S)-HETE (12-S-hydroxyeicosatetranoic acid) inhibited Na+,K+-ATPase activity, and this effect, as well as that of glucose, was blocked by bisindolylmaleimide, a specific protein kinase C inhibitor. Moreover, glucose increased the state of alpha-subunit phosphorylation by a protein kinase C-dependent process. These results demonstrate that glucose inhibits Na+, K+-ATPase activity in beta-cells by activating a distinct intracellular signaling network. Inhibition of Na+,K+-ATPase activity may thus be part of the mechanisms whereby glucose promotes membrane depolarization, an increase in [Ca2+]i, and thereby insulin secretion in the pancreatic beta-cell.
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Affiliation(s)
- S Owada
- Rolf Luft Center for Diabetes Research L6B:01, Department of Molecular Medicine, Karolinska Institutet, Karolinska Hospital, S-171 76 Stockholm, Sweden
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25
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Efanova IB, Zaitsev SV, Zhivotovsky B, Köhler M, Efendić S, Orrenius S, Berggren PO. Glucose and tolbutamide induce apoptosis in pancreatic beta-cells. A process dependent on intracellular Ca2+ concentration. J Biol Chem 1998; 273:33501-7. [PMID: 9837930 DOI: 10.1074/jbc.273.50.33501] [Citation(s) in RCA: 266] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
High concentrations of glucose are considered to be toxic for the pancreatic beta-cell. However, the mechanisms underlying beta-cell dysfunction and resulting cell death are not fully characterized. In the present study we have demonstrated that incubation of pancreatic islets and beta-cells from ob/ob mice and Wistar rats with glucose induced a process of apoptotic beta-cell death, as shown by DNA laddering, TdT-mediated dUTP-biotin nick end-labeling (TUNEL) technique, and by using DNA-staining dye HOECHST 33342. The obtained results show that the percentage of apoptotic cells was dependent on glucose concentration, being minimal at 11 mM glucose. At a concentration of 100 microM, aurintricarboxylic acid, an inhibitor of endonuclease activity, almost completely inhibited apoptosis triggered by 17 mM glucose. We have also shown that long term incubation with 100 microM sulfonylurea, tolbutamide, triggered apoptosis in pancreatic beta-cells. The process of beta-cell death induced by high glucose concentration and tolbutamide were Ca2+-dependent, because introduction to the culture medium of 50 microM D-600 or 200 microM diazoxide, which blocked glucose- and tolbutamide-induced [Ca2+]i increase, inhibited apoptosis. Thus, this study shows for the first time that high glucose concentrations and tolbutamide induce apoptosis in pancreatic beta-cells, and that this process is Ca2+-dependent.
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Affiliation(s)
- I B Efanova
- The Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institute, Karolinska Hospital, S-171 76 Stockholm, Sweden
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26
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Sjöholm A. Aspects of novel sites of regulation of the insulin stimulus-secretion coupling in normal and diabetic pancreatic islets. Endocrine 1998; 9:1-13. [PMID: 9798725 DOI: 10.1385/endo:9:1:1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/16/1997] [Accepted: 02/12/1998] [Indexed: 11/11/2022]
Abstract
Noninsulin-dependent diabetes mellitus (NIDDM), a major health care problem in the Western world, is a disease typified by a relative deficiency of insulin, leading to vast derangements in glucose and lipid homeostasis with disastrous vascular complications. Despite immense research efforts aimed at a clear understanding of the etiology of this complex disease, the molecular mechanisms causing the disorder still remain elusive. This article reviews extant data from recent publications implicating novel signal transduction pathways as important regulators of the insulin stimulus-secretion coupling in the pancreatic beta-cell. The significance of nitric oxide and serine/threonine protein phosphatases, and their inactivation by insulin secretagogues, glucose metabolites, ATP, GTP, glutamate, and inositol hexaphosphate in this arena is scrutinized. Additionally, also presented is the growing concept that an important signal for insulin secretion may reside in the inextricable interplay between glucose and lipid metabolism, specifically the generation of malonyl-CoA, which inhibits carnitine palmitoyltransferase 1 with the attendant accumulation of long-chain acyl CoA esters. Moreover, attention is directed towards novel intracellular actions of hypoglycemic sulfonylureas in the beta-cell. Finally, the importance of "lipotoxicity" and aberrations in glucose uptake and metabolism in beta-cell dysfunction is given consideration. Future research efforts should aim at further characterization of effects of second messengers on protein phosphorylation elements in beta-cells. Additionally, long-term regulation by glucose and the diabetic state (e.g., fatty acids and ketones) on beta-cell protein phosphatases, pyruvate dehydrogenase, and carnitine palmitoyltransferase 1 needs to be explored in greater depth. Clearly, the detrimental impact of diabetic hyperlipidemia on beta-cell function has been a relatively neglected area, but futu re pharmacological approaches directed at preventing lipotoxicity may prove beneficial in the treatment of diabetes.
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Affiliation(s)
- A Sjöholm
- Department of Molecular Medicine, Karolinska Institute, Karolinska Hospital, Stockholm, Sweden
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27
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Kim SJ, Sung JJ, Park YS. L-type and dihydropyridine-resistant calcium channel trigger exocytosis with similar efficacy in single rat pancreatic beta cells. Biochem Biophys Res Commun 1998; 243:878-84. [PMID: 9501019 DOI: 10.1006/bbrc.1998.8197] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The relationship between depolarization-induced exocytosis and inward Ca2+ current (Ica) in single isolated rat pancreatic beta cells was investigated in perforated patch recordings. Ica was elicited by depolarization and change in cell membrane capacitance (Cm) was monitored as an indicator of resultant exocytosis. While there was significant variety of change in Cm and Ca2+ influx, the increase in Cm had positive correlation with Ca2+ influx and also with duration of depolarization. Removal of extracellular Ca2+ or inclusion of extracellular Cd2+ (100 microM) completely eliminated both Ica and increase in Cm following depolarization. Dihydropyridine (DHP) Ca2+ channel blocker (5 microM) partly and in parallel suppressed depolarization-induced peak Ica, Ca2+ influx, and change in Cm. These data suggest that rat pancreatic beta cell expresses at least two types of Ca2+ channels; Ca2+ entry through these DHP-sensitive, presumably L-type, and DHP-insensitive channels triggers exocytosis with similar efficacy.
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Affiliation(s)
- S J Kim
- Department of Physiology & Biophysics, Seoul National University, College of Medicine, Korea
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28
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Zhang Q, Berggren PO, Larsson O, Hall K, Tally M. Insulin-like growth factor II inhibits glucose-induced insulin exocytosis. Biochem Biophys Res Commun 1998; 243:117-21. [PMID: 9473490 DOI: 10.1006/bbrc.1997.8053] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
We have investigated the effect of IGF-II on glucose-induced insulin release in the pancreatic beta-cell. Introduction of IGF-II during perifusion of the cells with 20 mM glucose abolished glucose-induced insulin release. Concomitant addition of IGF-II with 20 mM glucose caused a complete inhibition of insulin release. In addition, IGF-II inhibited Ca(2+)-induced insulin release from electropermeabilized pancreatic beta-cells. IGF-II had no effect on K(+)-or tolbutamide-induced insulin release. However, IGF-II could suppress K(+)-stimulated insulin release when cells were pretreated with the protein phosphatase inhibitor okadaic acid. The inhibitory effect of IGF-II on insulin release was not associated with significant changes in membrane potential, activity of the voltage-gated L-type Ca(2+)-channel or cytoplasmic free Ca2+ concentration. Pretreatment of the cells with pertussis toxin or the phorbol ester TPA abolished the inhibitory action of IGF-II on insulin release. Hence, the molecular mechanism whereby activation of the IGF-II/M6P receptor by IGF-II inhibits glucose-stimulated insulin exocytosis in the pancreatic beta-cell involves pertussis toxin-sensitive G proteins and is dependent on PKC activity.
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Affiliation(s)
- Q Zhang
- Department of Molecular Medicine, Rolf Luft Center for Diabetes Research, Karolinska Institute, Karolinska Hospital, Stockholm, Sweden
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29
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Bränström R, Corkey BE, Berggren PO, Larsson O. Evidence for a unique long chain acyl-CoA ester binding site on the ATP-regulated potassium channel in mouse pancreatic beta cells. J Biol Chem 1997; 272:17390-4. [PMID: 9211879 DOI: 10.1074/jbc.272.28.17390] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The mechanism by which long chain acyl-CoA (LC-CoA) esters affect the ATP-regulated potassium channel (KATP channel) was studied in inside-out patches isolated from mouse pancreatic beta cells. Addition of LC-CoA esters dramatically increased KATP channel activity. The stimulatory effect of the esters could be explained by the induction of a prolonged open state of the channel and did not involve alterations in single channel unitary conductance. Under control conditions, absence of adenine nucleotides, the distribution of KATP channel open time could be described by a single exponential, with a time constant of about 25 ms. Exposing the same patch to LC-CoA esters resulted in the appearance of an additional component with a time constant of >>150 ms, indicating a conformational change of the channel protein. LC-CoA esters were also able to potently activate channel activity at different ratios of ATP/ADP. Simultaneous additions of MgADP and LC-CoA esters resulted in a supra-additive effect on channel mean open time, characterized by openings of very long duration. Following modification of the KATP channel by a short exposure of the patch to the protease trypsin, the stimulatory effect of ADP on channel activity was lost while activation by LC-CoA esters still persisted. This indicates that LC-CoA esters and MgADP do not bind to the same site. We conclude that LC-CoA esters may play an important role in the physiological regulation of the KATP channel in the pancreatic beta cell by binding to a unique site and thereby inducing repolarization of the beta cell-membrane potential.
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Affiliation(s)
- R Bränström
- The Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institute, S-171 76 Stockholm, Sweden
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30
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Zhang Q, Tally M, Larsson O, Kennedy RT, Huang L, Hall K, Berggren PO. Insulin-like growth factor II signaling through the insulin-like growth factor II/mannose-6-phosphate receptor promotes exocytosis in insulin-secreting cells. Proc Natl Acad Sci U S A 1997; 94:6232-7. [PMID: 9177200 PMCID: PMC21032 DOI: 10.1073/pnas.94.12.6232] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The insulin-like growth factor II (IGF-II)/mannose-6-phosphate (M-6-P) receptor is known to participate in endocytosis as well as sorting of lysosomal enzymes and is involved in membrane trafficking through rapid cycling between cytosolic membrane compartments and the plasma membrane. Here we demonstrate that IGF-II, acting through the IGF-II/M-6-P receptor, promotes exocytosis of insulin in the pancreatic beta cell. The effect of IGF-II was evoked at nonstimulatory concentrations of glucose, was mediated by a pertussis toxin sensitive GTP-binding protein, was dependent on protein kinase C-induced phosphorylation, and was independent of changes in cytoplasmic free Ca2+ concentration. Since the applied concentration of IGF-II is within the range normally found free in circulation in humans, this novel signaling pathway for the IGF-II/M-6-P receptor is likely to be involved in modulation of insulin exocytosis under physiological conditions.
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Affiliation(s)
- Q Zhang
- Department of Molecular Medicine, The Rolf Luft Center for Diabetes Research, Karolinska Institute, S-171 76 Stockholm, Sweden
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31
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Bordin S, Carneiro EM, Bosqueiro JR, Boschero AC. Tetracaine stimulates extracellular Ca2+-independent insulin release. Eur J Pharmacol 1997; 327:257-62. [PMID: 9200568 DOI: 10.1016/s0014-2999(97)89669-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The effect of the local anesthetic, tetracaine, on 45Ca efflux, cytoplasmic Ca2+ concentration [Ca2+]i and insulin secretion in pancreatic B-cells was studied. At a physiological level of [Ca2+]o, tetracaine (0.1-5 mM) dose-dependently inhibited insulin secretion induced by 22 mM glucose. Paradoxically, at the same glucose concentration but in the absence of external Ca2+, tetracaine dose-dependently increased insulin secretion. At a low glucose level (2.8 mM) tetracaine failed to affect secretion, either in the presence or absence of external Ca2+. At high (22 mM) or low (2.8 mM) glucose, [Ca2+]i was increased by tetracaine in a dose-dependent manner. Tetracaine (2 mM) also increased the 45Ca efflux from isolated islets. This effect was of the same magnitude at both low and high glucose concentrations, and was independent of the presence of extracellular Ca2+. Finally, tetracaine increased 45Ca efflux from islets perifused in the presence of thapsigargin. In conclusion, our data indicate that tetracaine releases Ca2+ from a thapsigargin-insensitive store in pancreatic B-cells. Under suitable experimental conditions, insulin release can be elicited by a [Ca2+]o-independent pathway. The existence of a ryanodine-like Ca2+ channel in pancreatic B-cells is proposed.
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Affiliation(s)
- S Bordin
- Departamento de Fisiologia e Biofísica, Instituto de Biologia, UNICAMP, Campinas, SP, Brasil
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32
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Webb DL, Islam MS, Efanov AM, Brown G, Köhler M, Larsson O, Berggren PO. Insulin exocytosis and glucose-mediated increase in cytoplasmic free Ca2+ concentration in the pancreatic beta-cell are independent of cyclic ADP-ribose. J Biol Chem 1996; 271:19074-9. [PMID: 8702579 DOI: 10.1074/jbc.271.32.19074] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Stimulation of pancreatic beta-cells by glucose gives rise to an increase in the cytoplasmic free calcium concentration ([Ca2+]i) and exocytosis of insulin. Cyclic adenosine 5'-diphosphate ribose (cADPR), a metabolite of beta-NAD+, has been reported to increase [Ca2+]i in pancreatic beta-cells by releasing Ca2+ from inositol 1,4,5-trisphosphate-insensitive intracellular stores. In the present study, we have examined the role of cADPR in glucose-mediated increases in [Ca2+]i and insulin exocytosis. Dispersed ob/ob mouse beta-cell aggregates were either pressure microinjected with fura-2 salt or loaded with fura-2 acetoxymethyl ester, and [Ca2+]i was monitored by microfluorimetry. Microinjection of beta-NAD+ into fura-2-loaded beta-cells did not increase [Ca2+]i nor did it alter the cells' subsequent [Ca2+]i response to glucose. Cells microinjected with the cADPR antagonist 8NH2-cADPR increased [Ca2+]i in response to glucose equally well as those injected with cADPR. Finally, the ability of cADPR to promote exocytosis of insulin in electropermeabilized beta-cells was investigated. cADPR on its own did not increase insulin secretion nor did it potentiate Ca2+-induced insulin secretion. We conclude that cADPR neither plays a significant role in glucose-mediated increases in [Ca2+]i nor interacts directly with the molecular mechanisms regulating exocytosis of insulin in normal pancreatic beta-cells.
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Affiliation(s)
- D L Webb
- Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institute, Karolinska Hospital, S-171 76 Stockholm, Sweden
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33
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Larsson O, Kindmark H, Brandstrom R, Fredholm B, Berggren PO. Oscillations in KATP channel activity promote oscillations in cytoplasmic free Ca2+ concentration in the pancreatic beta cell. Proc Natl Acad Sci U S A 1996; 93:5161-5. [PMID: 8643546 PMCID: PMC39425 DOI: 10.1073/pnas.93.10.5161] [Citation(s) in RCA: 78] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Pancreatic beta cells exhibit oscillations in electrical activity, cytoplasmic free Ca2+ concentration ([Ca2+](i)), and insulin release upon glucose stimulation. The mechanism by which these oscillations are generated is not known. Here we demonstrate fluctuations in the activity of the ATP-dependent K+ channels (K(ATP) channels) in single beta cells subject to glucose stimulation or to stimulation with low concentrations of tolbutamide. During stimulation with glucose or low concentrations of tolbutamide, K(ATP) channel activity decreased and action potentials ensued. After 2-3 min, despite continuous stimulation, action potentials subsided and openings of K(ATP) channels could again be observed. Transient suppression of metabolism by azide in glucose-stimulated beta cells caused reversible termination of electrical activity, mimicking the spontaneous changes observed with continuous glucose stimulation. Thus, oscillations in K(ATP) channel activity during continuous glucose stimulation result in oscillations in electrical activity and [Ca2+](i).
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Affiliation(s)
- O Larsson
- The Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institute, Karolinska Hospital, Stockholm, Sweden
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34
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Bode H, Himmen A, Göke B. Evidence for vacuolar-type proton pumps in nonmitochondrial and inositol 1,4,5-trisphosphate-sensitive calcium stores of insulin-secreting cells. Pflugers Arch 1996; 432:97-104. [PMID: 8662273 DOI: 10.1007/s004240050110] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
This study examines whether acidic, vacuolar-type, proton-pump-carrying organelles of insulin-secreting cells (clonal endocrine pancreatic cell line INS-1) function as rapidly exchanging, inositol 1,4,5-trisphosphate-sensitive calcium stores. Calcium uptake into calcium stores will be modulated by the proton concentration within the stores, since calcium pumps in general appear to mediate a countertransport of calcium with protons. We therefore tested for sensitivity of calcium sequestration by nonmitochondrial stores (inhibition of mitochondrial calcium uptake by 2 microM ruthenium red) in saponin-permeabilized cells to proton-conducting ionophores and proton pump inhibition, using this as a marker for involvement of acidic organelles. Calcium sequestration was partially inhibited by the protonophores nigericin (10-50 microM) and carbonylcyanide m-chlorophenylhydrazone (CCCP; 20-50 microM), as well as by inclusion of 30 mM NH4Cl. Bafilomycin A1, a potent and selective inhibitor of vacuolar-type proton pumps, alone (1 - 500 nM) had no effect on calcium sequestration. however, it induced an inhibitory effect in the presence of nigericin or CCCP, even at low concentrations (5 microM) of these ionophores, lacking itself an inhibitory action on calcium sequestration. Bafilomycin A1 then was already maximally active at a concentration as low as 10 nM. Corres ponding to inhibition of total nonmitochondrial calcium sequestration, filling of inositol 1,4,5-trisphosphate-sensitive stores was decreased or even abolished by the protonophores alone or the protonophores combined with bafilomycin A1. We conclude that vacuolar-type proton pumps are present in at least a part of nonmitochondrial and inositol 1,4,5-trisphosphate-sensitive calcium stores in INS-1 cells. This assigns these stores to organelles such as secretory granules, the trans Golgi network, or endosomes. Luminal acidity of these stores will stimulate calcium sequestration by providing more protons for countertransport of calcium by calcium pumps. High concentrations of protonophores may be required for inhibitory effects because otherwise the proton pumps may be able to compensate sufficiently for ionophore-mediated proton loss. The lack of effect of bafilomycin A1 without protonophores may be due to a sufficient luminal buffering capacity or to preceding inhibition of the pump by an inside-positive transmembrane potential.
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Affiliation(s)
- H Bode
- Department of Pharmacology, Philipps-University, Karl-von-Frisch-Strasse, D-35033 Marburg, Germany
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35
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Zaitsev SV, Efendić S, Arkhammar P, Bertorello AM, Berggren PO. Dissociation between changes in cytoplasmic free Ca2+ concentration and insulin secretion as evidenced from measurements in mouse single pancreatic islets. Proc Natl Acad Sci U S A 1995; 92:9712-6. [PMID: 7568203 PMCID: PMC40872 DOI: 10.1073/pnas.92.21.9712] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Simultaneous measurements of cytosolic free Ca2+ concentration and insulin release, in mouse single pancreatic islets, revealed a direct correlation only initially after stimulation with glucose or K+. Later, there is an apparent dissociation between these two parameters, with translocation of alpha and epsilon isoenzymes of protein kinase C to membranes and simultaneous desensitization of insulin release in response to glucose. Recovery of insulin release, without any concomitant changes in cytosolic free Ca2+ concentration, after addition of phorbol 12-myristate 13-acetate, okadaic acid, and forskolin supports the notion that the desensitization process is accounted for by dephosphorylation of key regulatory sites of the insulin exocytotic machinery.
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Affiliation(s)
- S V Zaitsev
- Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institute, Karolinska Hospital, Stockholm, Sweden
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36
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Yada T, Hamakawa N, Yaekura K. Two distinct modes of Ca2+ signalling by ACh in rat pancreatic beta-cells: concentration, glucose dependence and Ca2+ origin. J Physiol 1995; 488 ( Pt 1):13-24. [PMID: 8568649 PMCID: PMC1156697 DOI: 10.1113/jphysiol.1995.sp020942] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
1. Calcium signalling by acetylcholine (ACh) in single rat pancreatic beta-cells was studied. The cytosolic free Ca2+ concentration ([Ca2+]i) was measured by dual-wavelength fura-2 microfluorometry. 2. In the presence of basal glucose (2.8 mM), 10(-6) to 10(-4) M ACh (high ACh) transiently increased [Ca2+]i. The [Ca2+]i response to 10(-5) M ACh was little altered under Ca(2+)-free conditions. Brief pulses of 10(-5) M ACh evoked successive [Ca2+]i responses, which were progressively inhibited by 0.2-0.5 microM thapsigargin, a specific inhibitor of the endoplasmic reticulum (ER) Ca2+ pump. 3. Elevation of glucose to 8.3 mM, a concentration which stimulates insulin release, increased [Ca2+]i to an initial peak followed by a sustained, moderate elevation. Addition of 10(-8) to 10(-7) M ACh (low ACh) evoked a further increase in [Ca2+]i. The [Ca2+]i response to 10(-7) M ACh was completely inhibited under Ca(2+)-free conditions by 1 microM nitrendipine, a blocker of L-type Ca2+ channels, and by 100 microM diazoxide, an opener of ATP-sensitive K+ channels. 4. In the presence of 8.3 mM glucose, [Ca2+]i responses to 10(-5) M ACh were reduced but not abolished by Ca(2+)-free conditions, nitrendipine and diazoxide. Successive [Ca2+]i transients induced by 10(-5) M ACh pulses in the presence of nitrendipine were progressively inhibited by thapsigargin. 5. The results revealed two distinct modes of Ca2+ signalling: low ACh increases [Ca2+]i by stimulating Ca2+ influx through voltage-dependent L-type Ca2+ channels only in the beta-cells in which glucose has already elevated [Ca2+]i, while high ACh increases [Ca2+]i at basal as well as stimulatory glucose concentrations by releasing Ca2+ from the ER. The former mechanism is likely to relate to the potentiator action and the latter to the initiator action of ACh on insulin release. High ACh and elevated glucose provoke both modes of Ca2+ signalling.
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Affiliation(s)
- T Yada
- Department of Physiology, Kagoshima University School of Medicine, Japan
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37
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Billaudel BJ, Bourlon PM, Sutter BC, Faure-Dussert AG. Regulatory effect of 1,25-dihydroxyvitamin D3 on insulin release and calcium handling via the phospholipid pathway in islets from vitamin D-deficient rats. J Endocrinol Invest 1995; 18:673-82. [PMID: 8719297 DOI: 10.1007/bf03349788] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The effect of 10(-8) M 1,25-dihydroxyvitamin D3 [1,25 (OH)2D3] on the phosphoinositide pathway, was studied on [3H] inositol and 45Ca2+ efflux and on insulin release of islets from vitamin D-deficient rats, during an acetylcholine (Ach) stimulus in perifusion. The insulin release, which was low in vitamin D-deficient rats, was enhanced by this treatment. The 3H flux, reflecting phosphoinositide breakdown, was also increased. The 45Ca2+ flux was stimulated both during the first 14 min peak (mobilization of IP3-sensitive reticular Ca2+ stores) and during the following sustained small elevation of 45Ca2+ flux, reflecting protein kinase C (PKC) activation and consequently increased phosphorylation of Ca2+ channel proteins. These effects were larger during perifusions performed in the presence of glucose which is known to open Ca2+ channels, suggesting a synergistic influence of glucose and 1,25(OH)2D3. This positive influence of 1,25(OH)2D3 in Ca2+ entry by Ca2+ channels was confirmed by the use of nifedipine-a Ca2+ channel blocker-which suppressed the 45Ca2+ flux and lowered insulin secretion. Moreover, the sustained 45Ca2+ flux also disappeared in islets from vitamin D-deficient rats supplemented by 1,25(OH)2D3 but perifused without extracellular Ca2+ supporting the hypothesis of 1,25(OH)2D3-induced activation of PKC. Thus, 1,25(OH)2D3 may provide supplementary calcium to the B cell by regulating the intracellular signalling processes involving phospholipid metabolism, PKC induction, Ca2+ mobilization and Ca2+ entry by Ca2+ channels.
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Affiliation(s)
- B J Billaudel
- Laboratoire d'Endocrinologie, Université de Bordeaux I, France
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38
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Kindmark H, Køohler M, Larsson O, Khan A, Berggren PO. Dissociation between exocytosis and Ca(2+)-channel activity in mouse pancreatic beta-cells stimulated with calmidazolium (compound R24571). FEBS Lett 1995; 369:315-20. [PMID: 7649279 DOI: 10.1016/0014-5793(95)00774-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Calmidazolium, a calmodulin inhibitor, suppressed influx of Ca2+ through voltage-gated Ca2+ channels in mouse pancreatic beta-cells. Despite this fact, calmidazolium stimulated insulin release from beta-cells at basal glucose concentration. This effect was not mediated by protein kinase C (PKC), since it persisted in PKC-depleted cells. RpcAMPS significantly attenuated the calmidazolium-stimulated insulin secretion, indicating that calmidazolium acts, at least partly, through PKA. The compound also stimulated insulin secretion from electropermeabilized beta-cells, indicating effects on distal steps in the stimulus-secretion coupling. The use of calmidazolium offers possibilities to investigate the mechanisms activating exocytosis under conditions where the cytoplasmic-free Ca2+ concentration does not increase.
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Affiliation(s)
- H Kindmark
- Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Hospital, Stockholm, Sweden
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39
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Liu YJ, Grapengiesser E, Gylfe E, Hellman B. Glucose induces oscillations of cytoplasmic Ca2+, Sr2+ and Ba2+ in pancreatic beta-cells without participation of the thapsigargin-sensitive store. Cell Calcium 1995; 18:165-73. [PMID: 7585893 DOI: 10.1016/0143-4160(95)90007-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Individual pancreatic beta -cells were used to study the glucose effects on the handling of Ca2+, Sr2+ and Ba2+. In extracellular medium containing one of these ions, single beta -cells responded to 11 mM glucose with large amplitude oscillations in cytoplasmic Ca2+, Sr2+ or Ba2+ with indistinguishable average frequencies (0.30-0.33/min). The oscillations disappeared after hyperpolarization with 400 microM diazoxide. Under such hyperpolarization, glucose stimulated the sequestration of Ca2+ and Sr2+ but not of repetitively mobilized by consecutive exposures to 100 microM carbachol. A 2-3 min exposure to 100 nM of the intracellular Ca(2+)-ATPase inhibitor thapsigargin also mobilized Ca2+ and Sr2+ and irreversibly abolished subsequent release by carbachol. However, thapsigargin did not prevent the large amplitude oscillations in Ca2+, Sr2+ or Ba2+ under non-hyperpolarizing conditions although the frequency of the Ca2+ oscillations was almost doubled. The results indicate that the slow oscillatory behavior of glucose-stimulated individual beta -cells does not depend on inositol 1,4,5-trisphosphate mediated release of intracellular Ca2+.
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Affiliation(s)
- Y J Liu
- Department of Medical Cell Biology, Uppsala University, Sweden
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40
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Váradi A, Molnár E, Ashcroft SJ. Characterisation of endoplasmic reticulum and plasma membrane Ca(2+)-ATPases in pancreatic beta-cells and in islets of Langerhans. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1236:119-27. [PMID: 7794940 DOI: 10.1016/0005-2736(95)00103-a] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
We have investigated the plasma membrane (PMCA) and endoplasmic reticulum (SERCA) Ca(2+)-ATPases involved in active transport of Ca2+ in pancreatic beta-cell lines (MIN6, HIT T15, RINm5F) and in islets of Langerhans. Under selective membrane phosphorylation conditions (at low ATP concentration, in the presence of Ca2+ and La3+ and in the absence of Mg2+ at 4 degrees C) the only labelled proteins are the phosphoenzyme intermediates of the Ca(2+)-ATPases. Under these conditions, beta-cell membranes incorporated 32P from [gamma-32P]ATP into two proteins with molecular mass on acidic SDS-polyacrylamide gels of around 115 and 150 kDa. The 150 kDa band was identified as PMCA (i) by reaction with a monoclonal anti-human erythrocyte plasma membrane Ca(2+)-ATPase antibody; (ii) by its typical tryptic cleavage pattern which generated an 80 kDa band; (iii) by lack of inhibition of its autophosphorylation by SERCA-specific inhibitors. The 115 kDa band was identified as SERCA (i) by reaction with a polyclonal anti-rat fast skeletal muscle Ca(2+)-ATPase antibody; (ii) by the concentration-dependent inhibition of its autophosphorylation by thapsigargin and 2,5-di(t-butyl)-1,4-benzohydroquinone (tBHQ), which are specific inhibitors of SERCA. The 115 kDa band was further characterised as the SERCA-2b isoform by reaction with a polyclonal rabbit antibody against the 12 C-terminal amino acids of SERCA-2b.
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Affiliation(s)
- A Váradi
- Nuffield Department of Clinical Biochemistry, John Radcliffe Hospital, Headington, Oxford, UK
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41
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Islam MS, Larsson O, Nilsson T, Berggren PO. Effects of caffeine on cytoplasmic free Ca2+ concentration in pancreatic beta-cells are mediated by interaction with ATP-sensitive K+ channels and L-type voltage-gated Ca2+ channels but not the ryanodine receptor. Biochem J 1995; 306 ( Pt 3):679-86. [PMID: 7702559 PMCID: PMC1136574 DOI: 10.1042/bj3060679] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
In the pancreatic beta-cell, an increase in the cytoplasmic free Ca2+ concentration ([Ca2+]i) by caffeine is believed to indicate mobilization of Ca2+ from intracellular stores, through activation of a ryanodine receptor-like channel. It is not known whether other mechanisms, as well, underlie caffeine-induced changes in [Ca2+]i. We studied the effects of caffeine on [Ca2+]i by using dual-wavelength excitation microfluorimetry in fura-2-loaded beta-cells. In the presence of a non-stimulatory concentration of glucose, caffeine (10-50 mM) consistently increased [Ca2+]i. The effect was completely blocked by omission of extracellular Ca2+ and by blockers of the L-type voltage-gated Ca2+ channel, such as D-600 or nifedipine. Depletion of agonist-sensitive intracellular Ca2+ pools by thapsigargin did not inhibit the stimulatory effect of caffeine on [Ca2+]i. Moreover, this effect of caffeine was not due to an increase in cyclic AMP, since forskolin and 3-isobutyl-1-methylxanthine (IBMX) failed to raise [Ca2+]i in unstimulated beta-cells. In beta-cells, glucose and sulphonylureas increase [Ca2+]i by causing closure of ATP-sensitive K+ channels (KATP channels). Caffeine also caused inhibition of KATP channel activity, as measured in excised inside-out patches. Accordingly, caffeine (> 10 mM) induced insulin release from beta-cells in the presence of a non-stimulatory concentration of glucose (3 mM). Hence, membrane depolarization and opening of voltage-gated L-type Ca2+ channels were the underlying mechanisms whereby the xanthine drug increased [Ca2+]i and induced insulin release. Paradoxically, in glucose-stimulated beta-cells, caffeine (> 10 mM) lowered [Ca2+]i. This effect was due to the fact that caffeine reduced depolarization-induced whole-cell Ca2+ current through the L-type voltage-gated Ca2+ channel in a dose-dependent manner. Lower concentrations of caffeine (2.5-5.0 mM), when added after glucose-stimulated increase in [Ca2+]i, induced fast oscillations in [Ca2+]i. The latter effect was likely to be attributable to the cyclic AMP-elevating action of caffeine, leading to phosphorylation of voltage-gated Ca2+ channels. Hence, in beta-cells, caffeine-induced changes in [Ca2+]i are not due to any interaction with intracellular Ca2+ pools. In these cells, a direct interference with KATP channel- and L-type voltage-gated Ca(2+)-channel activity is the underlying mechanism by which caffeine increases or decreases [Ca2+]i.
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Affiliation(s)
- M S Islam
- Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institute, Karolinska Hospital, Stockholm, Sweden
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42
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Hamakawa N, Yada T. Interplay of glucose-stimulated Ca2+ sequestration and acetylcholine-induced Ca2+ release at the endoplasmic reticulum in rat pancreatic beta-cells. Cell Calcium 1995; 17:21-31. [PMID: 7553778 DOI: 10.1016/0143-4160(95)90099-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
It is known that the stimulation with high glucose initially decreases as well as subsequently increases the cytosolic free Ca2+ concentration ([Ca2+]i) in pancreatic beta-cells. In the present study, we aimed at exploring the ionic mechanism and physiological role of the glucose-induced decrease in [Ca2+]i by measuring [Ca2+]i in single pancreatic beta-cells from normal rats. The glucose-induced decrease in [Ca2+]i in beta-cells was completely inhibited by thapsigargin (Tg), a specific inhibitor of the endoplasmic reticulum (ER) Ca2+ pump (Ca(2+)-ATPase). On the other hand, neither a Ca(2+)-free nor a low-Na+ condition significantly altered the glucose-induced decrease in [Ca2+]i. At basal glucose concentrations (1-4.5 mM), an insulin secretagogue acetylcholine (ACh) evoked a rather transient increase in [Ca2+]i in the presence and absence of extracellular Ca2+. A rise in glucose concentration from 1 to 4.5 mM produced a sustained decrease in [Ca2+]i and concomitantly augmented the ACh-evoked increase in [Ca2+]i. The resting [Ca2+]i level determined by glucose was tightly and reciprocally correlated with the peak of the [Ca2+]i response to ACh. Successive ACh pulses elicited repeated [Ca2+]i responses, which were progressively inhibited by Tg, suggesting that Ca2+ released by ACh was taken up by the ER Ca2+ pump and thus cycled. The results demonstrate that glucose decreases [Ca2+]i in pancreatic beta-cells mainly by activating the Ca2+ pump in ER from which ACh mobilizes Ca2+. Furthermore, the glucose-stimulated sequestration of Ca2+ by ER results in an augmented [Ca2+]i response to ACh, providing a mechanistic basis for the glucose-dependent action of ACh to initiate insulin secretion.
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Affiliation(s)
- N Hamakawa
- Department of Physiology, Kagoshima University School of Medicine, Japan
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43
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Rutter GA, Theler JM, Li G, Wollheim CB. Ca2+ stores in insulin-secreting cells: lack of effect of cADP ribose. Cell Calcium 1994; 16:71-80. [PMID: 7982266 DOI: 10.1016/0143-4160(94)90002-7] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Ca2+ stores were examined in several insulin secreting cell types by measuring uptake and release of Ca2+ by permeabilised cells. In pancreatic islet cells or INS-1 cells, < 20% of the ATP-dependent, thapsigargin-sensitive Ca2+ pool could be released by saturating concentrations of inositol (1,4,5)P3 (InsP3). InsP3 released > 60% of the thapsigargin-sensitive Ca2+ pool in RINm5F cells. The total Ca2+ content of the thapsigargin-sensitive pool was similar in each of these cell types. Neither cADP ribose (cADPR; 1 microM) nor caffeine (10 mM) caused significant Ca2+ release from any of the permeabilised insulin-secreting cell preparations. ATP elicited similar increases in intracellular Ca2+ concentration ([Ca2+]i) in single, living INS-1 and RINm5F cells, and similar fold increases in InsP3 levels in cell populations. The Ca2+ ATPase inhibitor thapsigargin, added after ATP, caused smaller [Ca2+]i increases in RINm5F than in INS-1 cells. This is consistent with the presence of a smaller InsP3-sensitive Ca2+ pool in living INS-1 cells. The data indicate that InsP3 receptors are present in only a small subfraction of the Ca2+ ATPase-containing Ca2+ stores in INS-1 and pancreatic beta-cells, and that cADP ribose/caffeine-sensitive Ca(2+)-induced Ca2+ release channels may be entirely absent from this endocrine cell type.
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Affiliation(s)
- G A Rutter
- Department of Medicine, University of Geneva, Switzerland
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Kindmark H, Köhler M, Gerwins P, Larsson O, Khan A, Wahl MA, Berggren PO. The imidazoline derivative calmidazolium inhibits voltage-gated Ca(2+)-channels and insulin release but has no effect on the phospholipase C system in insulin producing RINm5F-cells. Biosci Rep 1994; 14:145-58. [PMID: 7833453 DOI: 10.1007/bf01240247] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The present study shows that the calmodulin antagonist calmidazolium inhibited influx of Ca2+ through voltage-gated Ca(2+)-channels in clonal insulin producing RINm5F-cells. The mechanism of inhibition may involve both Ca(2+)-calmodulin-dependent protein kinases and direct binding of calmidazolium to the Ca(2+)-channel. Calmidazolium did not affect uptake of Ca2+ into intracellular Ca(2+)-pools, inositol 1,4,5-trisphosphate (InsP3) formation or action on intracellular Ca(2+)-pools. The calmodulin inhibitor also did not affect glucose utilization or oxidation in RINm5F-cells, speaking against an unspecific toxic effect of the compound. KCl-and ATP-stimulated insulin release from RINm5F-cells was attenuated by calmidazolium, whereas basal hormone secretion was unaffected.
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Affiliation(s)
- H Kindmark
- Department of Pharmacology, Karolinska Institute, Stockholm, Sweden
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Barker CJ, Nilsson T, Kirk CJ, Michell RH, Berggren PO. Simultaneous oscillations of cytoplasmic free Ca2+ concentration and Ins(1,4,5)P3 concentration in mouse pancreatic beta-cells. Biochem J 1994; 297 ( Pt 2):265-8. [PMID: 8297329 PMCID: PMC1137823 DOI: 10.1042/bj2970265] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Changes in the cytoplasmic free Ca2+ concentration ([Ca2+]i) in stimulated cells are often oscillatory, but the mechanisms that drive these oscillations are still a matter of controversy: different models of the generation of these [Ca2+]i oscillations make different assumptions as to whether oscillations in Ins(1,4,5)P3 concentration are necessary for this process. We have looked for changes in inositol polyphosphate levels that might occur in suspensions of murine pancreatic beta-cells when these cells are induced to display synchronized oscillations in [Ca2+]i by the sequential addition of glucose, an alpha 2-adrenergic stimulus and extracellular Ca2+. The intracellular level of Ins(1,4,5)P3 oscillated in a manner approximately in synchrony with changes in [Ca2+]i. Oscillations in the levels of Ins(1,4,5)P3 metabolites [Ins(1,3,4)P3 and inositol bisphosphates] were slightly delayed relative to the Ins(1,4,5)P3 oscillations, and the concentration of Ins(1,3,4,5,6)P5 remained approximately constant during the [Ca2+]i oscillations. These results demonstrate that [Ins(1,4,5)P3] and [Ca2+]i oscillate in synchrony in at least one type of cell. Whether such oscillations in intracellular [Ins(1,4,5)P3] provide a primary driving force for [Ca2+]i oscillations either in beta-cells or in other stimulated cells remains to be determined. Even if they do not, the [Ins(1,4,5)P3] oscillations will at least provide an amplifying influence on the [Ca2+]i changes.
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Affiliation(s)
- C J Barker
- Centre for Clinical Research in Immunology and Signalling, University of Birmingham, Edgbaston, U.K
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Arkhammar P, Juntti-Berggren L, Larsson O, Welsh M, Nånberg E, Sjöholm A, Köhler M, Berggren P. Protein kinase C modulates the insulin secretory process by maintaining a proper function of the beta-cell voltage-activated Ca2+ channels. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)42006-0] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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Lee HC, Galione A, Walseth TF. Cyclic ADP-ribose: metabolism and calcium mobilizing function. VITAMINS AND HORMONES 1994; 48:199-257. [PMID: 7941427 DOI: 10.1016/s0083-6729(08)60499-9] [Citation(s) in RCA: 87] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- H C Lee
- Department of Physiology, University of Minnesota, Minneapolis
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48
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Sjöholm A, Arkhammar P, Welsh N, Bokvist K, Rorsman P, Hallberg A, Nilsson T, Welsh M, Berggren PO. Enhanced stimulus-secretion coupling in polyamine-depleted rat insulinoma cells. An effect involving increased cytoplasmic Ca2+, inositol phosphate generation, and phorbol ester sensitivity. J Clin Invest 1993; 92:1910-7. [PMID: 8408643 PMCID: PMC288357 DOI: 10.1172/jci116784] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
To extend previous observations on the role of polyamines in insulin production, metabolism, and replication of insulin-secreting pancreatic beta cells, we have studied the role of polyamines in the regulation of the stimulus-secretion coupling of clonal rat insulinoma cells (RINm5F). For this purpose, RINm5F cells were partially depleted in their polyamine contents by use of the specific ornithine decarboxylase inhibitor difluoromethylornithine (DFMO), which led to an increase in cellular insulin and ATP contents. Analysis of different parts of the signal transduction pathway revealed that insulin secretion and the increase in cytoplasmic free Ca2+ concentration ([Ca2+]i) after K(+)-induced depolarization were markedly enhanced in DFMO-treated cells. These effects were paralleled by increased voltage-activated Ca2+ currents, as judged by whole-cell patch-clamp analysis, probably reflecting increased channel activity rather than elevated number of channels per cell. DFMO treatment also rendered phospholipase C in these cells more sensitive to the muscarinic receptor agonist carbamylcholine, as evidenced by enhanced generation of inositol phosphates, increase in [Ca2+]i and insulin secretion, despite an unaltered ligand binding to muscarinic receptors and lack of effect on protein kinase C activity. In addition, the tumor promoter 12-O-tetradecanoylphorbol 13-acetate, at concentrations suggested to be specific for protein kinase C activation, evoked an increased insulin output in polyamine-deprived cells compared to control cells. The stimulatory effects of glucose or the cyclic AMP raising agent theophylline on insulin release were not increased by DFMO treatment. In spite of increased binding of sulfonylurea in DFMO-treated cells, there was no secretory response or altered increase in [Ca2+]i in response to the drug in these cells. It is concluded that partial polyamine depletion sensitizes the stimulus-secretion coupling at multiple levels in the insulinoma cells, including increased voltage-dependent Ca2+ influx and enhanced responsiveness to activators of phospholipase C and protein kinase C. In their entirety, our present results indicate that the behavior of the stimulus-secretion coupling of polyamine-depleted RINm5F insulinoma cells changes towards that of native beta cells, thus improving the usefulness of this cell line for studies of beta cell insulin secretion.
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Affiliation(s)
- A Sjöholm
- Department of Endocrinology, Rolf Luft Center for Diabetes Research, Karolinska Hospital, Stockholm, Sweden
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Islam MS, Berggren PO. Mobilization of Ca2+ by thapsigargin and 2,5-di-(t-butyl)-1,4-benzohydroquinone in permeabilized insulin-secreting RINm5F cells: evidence for separate uptake and release compartments in inositol 1,4,5-trisphosphate-sensitive Ca2+ pool. Biochem J 1993; 293 ( Pt 2):423-9. [PMID: 8343123 PMCID: PMC1134377 DOI: 10.1042/bj2930423] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We characterized and directly compared the Ca(2+)-releasing actions of two inhibitors of endoplasmic-reticulum (ER) Ca(2+)-ATPase, thapsigargin and 2,5-di-(t-butyl)-1,4-benzohydroquinone (tBuBHQ), in electropermeabilized insulin-secreting RINm5F cells. Ambient free calcium concentration ([Ca2+]) was monitored by Ca(2+)-selective mini-electrodes. After ATP-dependent Ca2+ uptake, thapsigargin and tBuBHQ released Ca2+ with and EC50 of approximately 37 nM and approximately 2 microM respectively. Both agents mobilized Ca2+ predominantly from the Ins(1,4,5)P3-sensitive Ca2+ pool, and in this respect thapsigargin was more specific than tBuBHQ. The total increase in [Ca2+] obtained with thapsigargin and Ins(1,4,5)P3 was, on the average, only 7% greater than that with Ins(1,4,5)P3 alone. In contrast, the total increase in [Ca2+] obtained with tBuBHQ and Ins(1,4,5)P3 was 33% greater than that obtained with only InsP3 (P < 0.05). Although Ca2+ was rapidly mobilized by thapsigargin and tBuBHQ, complete depletion of the Ins(1,4,5)P3-sensitive Ca2+ pool was difficult to achieve. After the release by thapsigargin or tBuBHQ, Ins(1,4,5)P3 induced additional Ca2+ release. The additional Ins(1,4,5)P3-induced Ca2+ release was not altered by supramaximal concentrations of thapsigargin and tBuBHQ, or by Bafilomycin A1, an inhibitor of V-type ATPases, but was decreased by prolonged treatment with the ER Ca(2+)-ATPase inhibitors. These results suggest the existence of distinct uptake and release compartments within the Ins(1,4,5)P3-sensitive Ca2+ pool. When treated with the inhibitors, the two compartments became distinguishable on the basis of their Ca2+ permeability. Apparently, thapsigargin and tBuBHQ readily mobilized Ca2+ from the uptake compartment, whereas Ca2+ from the release compartment could be mobilized only very slowly, in the absence of Ins(1,4,5)P3.
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Affiliation(s)
- M S Islam
- Rolf Luft Center for Diabetes Research, Department of Edocrinology, Karolinska Institute, Karolinska Hospital, Stockholm, Sweden
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