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Kamat V, Sweet IR. Hypertonicity during a rapid rise in D-glucose mediates first-phase insulin secretion. Front Endocrinol (Lausanne) 2024; 15:1395028. [PMID: 38989001 PMCID: PMC11233695 DOI: 10.3389/fendo.2024.1395028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/02/2024] [Accepted: 06/10/2024] [Indexed: 07/12/2024] Open
Abstract
Introduction Biphasic insulin secretion is an intrinsic characteristic of the pancreatic islet and has clinical relevance due to the loss of first-phase in patients with Type 2 diabetes. As it has long been shown that first-phase insulin secretion only occurs in response to rapid changes in glucose, we tested the hypothesis that islet response to an increase in glucose is a combination of metabolism plus an osmotic effect where hypertonicity is driving first-phase insulin secretion. Methods Experiments were performed using perifusion analysis of rat, mouse, and human islets. Insulin secretion rate (ISR) and other parameters associated with its regulation were measured in response to combinations of D-glucose and membrane-impermeable carbohydrates (L-glucose or mannitol) designed to dissect the effect of hypertonicity from that of glucose metabolism. Results Remarkably, the appearance of first-phase responses was wholly dependent on changes in tonicity: no first-phase in NAD(P)H, cytosolic calcium, cAMP secretion rate (cAMP SR), or ISR was observed when increased D-glucose concentration was counterbalanced by decreases in membrane-impermeable carbohydrates. When D-glucose was greater than 8 mM, rapid increases in L-glucose without any change in D-glucose resulted in first-phase responses in all measured parameters that were kinetically similar to D-glucose. First-phase ISR was completely abolished by H89 (a non-specific inhibitor of protein kinases) without affecting first-phase calcium response. Defining first-phase ISR as the difference between glucose-stimulated ISR with and without a change in hypertonicity, the peak of first-phase ISR occurred after second-phase ISR had reached steady state, consistent with the well-established glucose-dependency of mechanisms that potentiate glucose-stimulated ISR. Discussion The data collected in this study suggests a new model of glucose-stimulated biphasic ISR where first-phase ISR derives from (and after) a transitory amplification of second-phase ISR and driven by hypertonicity-induced rise in H89-inhibitable kinases likely driven by first-phase responses in cAMP, calcium, or a combination of both.
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Affiliation(s)
| | - Ian R. Sweet
- University of Washington Medicine Diabetes Institute, University of Washington, Seattle, WA, United States
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2
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Röthe J, Kraft R, Ricken A, Kaczmarek I, Matz-Soja M, Winter K, Dietzsch AN, Buchold J, Ludwig MG, Liebscher I, Schöneberg T, Thor D. The adhesion GPCR GPR116/ADGRF5 has a dual function in pancreatic islets regulating somatostatin release and islet development. Commun Biol 2024; 7:104. [PMID: 38228886 PMCID: PMC10791652 DOI: 10.1038/s42003-024-05783-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2023] [Accepted: 01/05/2024] [Indexed: 01/18/2024] Open
Abstract
Glucose homeostasis is maintained by hormones secreted from different cell types of the pancreatic islets and controlled by manifold input including signals mediated through G protein-coupled receptors (GPCRs). RNA-seq analyses revealed expression of numerous GPCRs in mouse and human pancreatic islets, among them Gpr116/Adgrf5. GPR116 is an adhesion GPCR mainly found in lung and required for surfactant secretion. Here, we demonstrate that GPR116 is involved in the somatostatin release from pancreatic delta cells using a whole-body as well as a cell-specific knock-out mouse model. Interestingly, the whole-body GPR116 deficiency causes further changes such as decreased beta-cell mass, lower number of small islets, and reduced pancreatic insulin content. Glucose homeostasis in global GPR116-deficient mice is maintained by counter-acting mechanisms modulating insulin degradation. Our data highlight an important function of GPR116 in controlling glucose homeostasis.
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Affiliation(s)
- Juliane Röthe
- Rudolf Schönheimer Institute of Biochemistry, Medical Faculty, Leipzig University, Leipzig, Germany
| | - Robert Kraft
- Carl-Ludwig-Institute for Physiology, Medical Faculty, Leipzig University, Leipzig, Germany
| | - Albert Ricken
- Institute of Anatomy, Medical Faculty, Leipzig University, Leipzig, Germany
| | - Isabell Kaczmarek
- Rudolf Schönheimer Institute of Biochemistry, Medical Faculty, Leipzig University, Leipzig, Germany
| | - Madlen Matz-Soja
- Medical Department II - Gastroenterology, Hepatology, Infectious Diseases, Pneumology, University Medical Center, Leipzig, Germany
- Division of Hepatology, Clinic and Polyclinic for Oncology, Gastroenterology, Hepatology, Infectious Diseases, and Pneumology, University Hospital, Leipzig, Germany
| | - Karsten Winter
- Institute of Anatomy, Medical Faculty, Leipzig University, Leipzig, Germany
| | - André Nguyen Dietzsch
- Rudolf Schönheimer Institute of Biochemistry, Medical Faculty, Leipzig University, Leipzig, Germany
| | - Julia Buchold
- Rudolf Schönheimer Institute of Biochemistry, Medical Faculty, Leipzig University, Leipzig, Germany
| | | | - Ines Liebscher
- Rudolf Schönheimer Institute of Biochemistry, Medical Faculty, Leipzig University, Leipzig, Germany
| | - Torsten Schöneberg
- Rudolf Schönheimer Institute of Biochemistry, Medical Faculty, Leipzig University, Leipzig, Germany
| | - Doreen Thor
- Rudolf Schönheimer Institute of Biochemistry, Medical Faculty, Leipzig University, Leipzig, Germany.
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3
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Kostritskaia Y, Klüssendorf M, Pan YE, Hassani Nia F, Kostova S, Stauber T. Physiological Functions of the Volume-Regulated Anion Channel VRAC/LRRC8 and the Proton-Activated Chloride Channel ASOR/TMEM206. Handb Exp Pharmacol 2024; 283:181-218. [PMID: 37468723 DOI: 10.1007/164_2023_673] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/21/2023]
Abstract
Volume-regulated anion channels (VRACs) and the acid-sensitive outwardly rectifying anion channel (ASOR) mediate flux of chloride and small organic anions. Although known for a long time, they were only recently identified at the molecular level. VRACs are heteromers consisting of LRRC8 proteins A to E. Combining the essential LRRC8A with different LRRC8 paralogues changes key properties of VRAC such as conductance or substrate selectivity, which is how VRACs are involved in multiple physiological functions including regulatory volume decrease, cell proliferation and migration, cell death, purinergic signalling, fat and glucose metabolism, insulin signalling, and spermiogenesis. VRACs are also involved in pathological conditions, such as the neurotoxic release of glutamate and aspartate. Certain VRACs are also permeable to larger, organic anions, including antibiotics and anti-cancer drugs, making them an interesting therapeutic target. ASOR, also named proton-activated chloride channel (PAC), is formed by TMEM206 homotrimers on the plasma membrane and on endosomal compartments where it mediates chloride flux in response to extracytosolic acidification and plays a role in the shrinking and maturation of macropinosomes. ASOR has been shown to underlie neuronal swelling which causes cell death after stroke as well as promoting the metastasis of certain cancers, making them intriguing therapeutic targets as well.
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Affiliation(s)
- Yulia Kostritskaia
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Malte Klüssendorf
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Yingzhou Edward Pan
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Fatemeh Hassani Nia
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Simona Kostova
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Tobias Stauber
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany.
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Calamita G, Delporte C. Insights into the Function of Aquaporins in Gastrointestinal Fluid Absorption and Secretion in Health and Disease. Cells 2023; 12:2170. [PMID: 37681902 PMCID: PMC10486417 DOI: 10.3390/cells12172170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2023] [Revised: 08/16/2023] [Accepted: 08/17/2023] [Indexed: 09/09/2023] Open
Abstract
Aquaporins (AQPs), transmembrane proteins permeable to water, are involved in gastrointestinal secretion. The secretory products of the glands are delivered either to some organ cavities for exocrine glands or to the bloodstream for endocrine glands. The main secretory glands being part of the gastrointestinal system are salivary glands, gastric glands, duodenal Brunner's gland, liver, bile ducts, gallbladder, intestinal goblet cells, exocrine and endocrine pancreas. Due to their expression in gastrointestinal exocrine and endocrine glands, AQPs fulfill important roles in the secretion of various fluids involved in food handling. This review summarizes the contribution of AQPs in physiological and pathophysiological stages related to gastrointestinal secretion.
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Affiliation(s)
- Giuseppe Calamita
- Department of Biosciences, Biotechnologies and Environment, University of Bari Aldo Moro, 70125 Bari, Italy;
| | - Christine Delporte
- Laboratory of Pathophysiological and Nutritional Biochemistry, Faculty of Medicine, Université Libre de Bruxelles, 1070 Brussels, Belgium
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Calamita G, Delporte C. Aquaporins in Glandular Secretion. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1398:225-249. [PMID: 36717498 DOI: 10.1007/978-981-19-7415-1_16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Exocrine and endocrine glands deliver their secretory product, respectively, at the surface of the target organs or within the bloodstream. The release of their products has been shown to rely on secretory mechanisms often involving aquaporins (AQPs). This chapter will provide insight into the role of AQPs in secretory glands located within the gastrointestinal tract, including salivary glands, gastric glands, duodenal Brunner's glands, liver, gallbladder, intestinal goblets cells, and pancreas, as well and in other parts of the body, including airway submucosal glands, lacrimal glands, mammary glands, and eccrine sweat glands. The involvement of AQPs in both physiological and pathophysiological conditions will also be highlighted.
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Affiliation(s)
- Giuseppe Calamita
- Department of Biosciences, Biotechnologies and Environment, University of Bari "Aldo Moro", Bari, Italy
| | - Christine Delporte
- Laboratory of Pathophysiological and Nutritional Biochemistry, Faculty of Medicine, Université Libre de Bruxelles, Brussels, Belgium.
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6
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Ponomareva S, Joisten H, François T, Naud C, Morel R, Hou Y, Myers T, Joumard I, Dieny B, Carriere M. Magnetic particles for triggering insulin release in INS-1E cells subjected to a rotating magnetic field. NANOSCALE 2022; 14:13274-13283. [PMID: 36056640 DOI: 10.1039/d2nr02009b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Diabetes is a major global health threat. Both academics and industry are striving to develop effective treatments for this disease. In this work, we present a new approach to induce insulin release from β-islet pancreatic cells (INS-1E) by mechanical stimulation. Two types of experiments were carried out. First, a local stimulation was performed by dispersing anisotropic magnetic particles within the cell medium, which settled down almost immediately on cell plasma membranes. Application of a low frequency magnetic field (up to 40 Hz) generated by a custom-made magnetic device resulted in oscillations of these particles, which then exerted a mechanical constraint on the cell plasma membranes. The second type of experiment consisted of a global stimulation, where cells were grown on magneto-elastic membranes composed of a biocompatible polymer with embedded magnetic particles. Upon application of a rotating magnetic field, magnetic particles within the membrane were attracted towards the field source, resulting in the membrane's vibrations being transmitted to the cells grown on it. In both experiments, the cell response to these mechanical stimulations caused by application of the variable magnetic field was quantified via the measurement of insulin release in the growth medium. We demonstrated that the mechanical action induced by the motion of magnetic particles or by membrane vibrations was an efficient stimulus for insulin granule secretion from β-cells. This opens a wide range of possible applications including the design of a system which triggers insulin secretion by β-islet pancreatic cells on demand.
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Affiliation(s)
- Svetlana Ponomareva
- Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG, SPINTEC, 38000 Grenoble, France.
| | - Helene Joisten
- Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG, SPINTEC, 38000 Grenoble, France.
- Univ. Grenoble Alpes, CEA, Leti, 38000 Grenoble, France
| | - Taina François
- Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG, SYMMES, 38000 Grenoble, France.
| | - Cecile Naud
- Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG, SPINTEC, 38000 Grenoble, France.
| | - Robert Morel
- Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG, SPINTEC, 38000 Grenoble, France.
| | - Yanxia Hou
- Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG, SYMMES, 38000 Grenoble, France.
| | - Thomas Myers
- Platform Kinetics, Pegholme, Wharfebank Mills, Otley, LS21 3JP, UK
| | - Isabelle Joumard
- Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG, SPINTEC, 38000 Grenoble, France.
| | - Bernard Dieny
- Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG, SPINTEC, 38000 Grenoble, France.
| | - Marie Carriere
- Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, IRIG, SYMMES, 38000 Grenoble, France.
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A critical role of the mechanosensor PIEZO1 in glucose-induced insulin secretion in pancreatic β-cells. Nat Commun 2022; 13:4237. [PMID: 35869052 PMCID: PMC9307633 DOI: 10.1038/s41467-022-31103-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2019] [Accepted: 06/06/2022] [Indexed: 11/08/2022] Open
Abstract
Glucose-induced insulin secretion depends on β-cell electrical activity. Inhibition of ATP-regulated potassium (KATP) channels is a key event in this process. However, KATP channel closure alone is not sufficient to induce β-cell electrical activity; activation of a depolarizing membrane current is also required. Here we examine the role of the mechanosensor ion channel PIEZO1 in this process. Yoda1, a specific PIEZO1 agonist, activates a small membrane current and thereby triggers β-cell electrical activity with resultant stimulation of Ca2+-influx and insulin secretion. Conversely, the PIEZO1 antagonist GsMTx4 reduces glucose-induced Ca2+-signaling, electrical activity and insulin secretion. Yet, PIEZO1 expression is elevated in islets from human donors with type-2 diabetes (T2D) and a rodent T2D model (db/db mouse), in which insulin secretion is reduced. This paradox is resolved by our finding that PIEZO1 translocates from the plasmalemma into the nucleus (where it cannot influence the membrane potential of the β-cell) under experimental conditions emulating T2D (high glucose culture). β-cell-specific Piezo1-knockout mice show impaired glucose tolerance in vivo and reduced glucose-induced insulin secretion, β-cell electrical activity and Ca2+ elevation in vitro. These results implicate mechanotransduction and activation of PIEZO1, via intracellular accumulation of glucose metabolites, as an important physiological regulator of insulin secretion.
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8
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Tentonin 3/TMEM150C regulates glucose-stimulated insulin secretion in pancreatic β-cells. Cell Rep 2021; 37:110067. [PMID: 34852221 DOI: 10.1016/j.celrep.2021.110067] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Revised: 10/17/2021] [Accepted: 11/08/2021] [Indexed: 11/24/2022] Open
Abstract
Glucose homeostasis is initially regulated by the pancreatic hormone insulin. Glucose-stimulated insulin secretion in β-cells is composed of two cellular mechanisms: a high glucose concentration not only depolarizes the membrane potential of the β-cells by ATP-sensitive K+ channels but also induces cell inflation, which is sufficient to release insulin granules. However, the molecular identity of the stretch-activated cation channel responsible for the latter pathway remains unknown. Here, we demonstrate that Tentonin 3/TMEM150C (TTN3), a mechanosensitive channel, contributes to glucose-stimulated insulin secretion by mediating cation influx. TTN3 is expressed specifically in β-cells and mediates cation currents to glucose and hypotonic stimulations. The glucose-induced depolarization, firing activity, and Ca2+ influx of β-cells were significantly lower in Ttn3-/- mice. More importantly, Ttn3-/- mice show impaired glucose tolerance with decreased insulin secretion in vivo. We propose that TTN3, as a stretch-activated cation channel, contributes to glucose-stimulated insulin secretion.
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9
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Calamita G, Delporte C. Involvement of aquaglyceroporins in energy metabolism in health and disease. Biochimie 2021; 188:20-34. [PMID: 33689852 DOI: 10.1016/j.biochi.2021.03.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 02/23/2021] [Accepted: 03/01/2021] [Indexed: 11/27/2022]
Abstract
Aquaglyceroporins are a group of the aquaporin (AQP) family of transmembrane water channels. While AQPs facilitate the passage of water, small solutes, and gases across biological membranes, aquaglyceroporins allow passage of water, glycerol, urea and some other solutes. Thanks to their glycerol permeability, aquaglyceroporins are involved in energy homeostasis. This review provides an overview of what is currently known concerning the functional implication and control of aquaglyceroporins in tissues involved in energy metabolism, i.e. liver, adipose tissue and endocrine pancreas. The expression, role and (dys)regulation of aquaglyceroporins in disorders affecting energy metabolism, and the potential relevance of aquaglyceroporins as drug targets to treat the alterations of the energy balance is also addressed.
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Affiliation(s)
- Giuseppe Calamita
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari "Aldo Moro", Bari, Italy
| | - Christine Delporte
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium.
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10
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An alternative pathway for sweet sensation: possible mechanisms and physiological relevance. Pflugers Arch 2020; 472:1667-1691. [PMID: 33030576 DOI: 10.1007/s00424-020-02467-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Revised: 09/14/2020] [Accepted: 09/23/2020] [Indexed: 12/12/2022]
Abstract
Sweet substances are detected by taste-bud cells upon binding to the sweet-taste receptor, a T1R2/T1R3 heterodimeric G protein-coupled receptor. In addition, experiments with mouse models lacking the sweet-taste receptor or its downstream signaling components led to the proposal of a parallel "alternative pathway" that may serve as metabolic sensor and energy regulator. Indeed, these mice showed residual nerve responses and behavioral attraction to sugars and oligosaccharides but not to artificial sweeteners. In analogy to pancreatic β cells, such alternative mechanism, to sense glucose in sweet-sensitive taste cells, might involve glucose transporters and KATP channels. Their activation may induce depolarization-dependent Ca2+ signals and release of GLP-1, which binds to its receptors on intragemmal nerve fibers. Via unknown neuronal and/or endocrine mechanisms, this pathway may contribute to both, behavioral attraction and/or induction of cephalic-phase insulin release upon oral sweet stimulation. Here, we critically review the evidence for a parallel sweet-sensitive pathway, involved signaling mechanisms, neural processing, interactions with endocrine hormonal mechanisms, and its sensitivity to different stimuli. Finally, we propose its physiological role in detecting the energy content of food and preparing for digestion.
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Chloride transporters and channels in β-cell physiology: revisiting a 40-year-old model. Biochem Soc Trans 2020; 47:1843-1855. [PMID: 31697318 PMCID: PMC6925527 DOI: 10.1042/bst20190513] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Revised: 10/14/2019] [Accepted: 10/17/2019] [Indexed: 12/13/2022]
Abstract
It is accepted that insulin-secreting β-cells release insulin in response to glucose even in the absence of functional ATP-sensitive K+ (KATP)-channels, which play a central role in a 'consensus model' of secretion broadly accepted and widely reproduced in textbooks. A major shortcoming of this consensus model is that it ignores any and all anionic mechanisms, known for more than 40 years, to modulate β-cell electrical activity and therefore insulin secretion. It is now clear that, in addition to metabolically regulated KATP-channels, β-cells are equipped with volume-regulated anion (Cl-) channels (VRAC) responsive to glucose concentrations in the range known to promote electrical activity and insulin secretion. In this context, the electrogenic efflux of Cl- through VRAC and other Cl- channels known to be expressed in β-cells results in depolarization because of an outwardly directed Cl- gradient established, maintained and regulated by the balance between Cl- transporters and channels. This review will provide a succinct historical perspective on the development of a complex hypothesis: Cl- transporters and channels modulate insulin secretion in response to nutrients.
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Deivasikamani V, Dhayalan S, Abudushalamu Y, Mughal R, Visnagri A, Cuthbertson K, Scragg JL, Munsey TS, Viswambharan H, Muraki K, Foster R, Sivaprasadarao A, Kearney MT, Beech DJ, Sukumar P. Piezo1 channel activation mimics high glucose as a stimulator of insulin release. Sci Rep 2019; 9:16876. [PMID: 31727906 PMCID: PMC6856185 DOI: 10.1038/s41598-019-51518-w] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Accepted: 09/25/2019] [Indexed: 12/11/2022] Open
Abstract
Glucose and hypotonicity induced cell swelling stimulate insulin release from pancreatic β-cells but the mechanisms are poorly understood. Recently, Piezo1 was identified as a mechanically-activated nonselective Ca2+ permeable cationic channel in a range of mammalian cells. As cell swelling induced insulin release could be through stimulation of Ca2+ permeable stretch activated channels, we hypothesised a role for Piezo1 in cell swelling induced insulin release. Two rat β-cell lines (INS-1 and BRIN-BD11) and freshly-isolated mouse pancreatic islets were studied. Intracellular Ca2+ measurements were performed using the fura-2 Ca2+ indicator dye and ionic current was recorded by whole cell patch-clamp. Piezo1 agonist Yoda1, a competitive antagonist of Yoda1 (Dooku1) and an inactive analogue of Yoda1 (2e) were used as chemical probes. Piezo1 mRNA and insulin secretion were measured by RT-PCR and ELISA respectively. Piezo1 mRNA was detected in both β-cell lines and mouse islets. Yoda1 evoked Ca2+ entry was inhibited by Yoda1 antagonist Dooku1 as well as other Piezo1 inhibitors gadolinium and ruthenium red, and not mimicked by 2e. Yoda1, but not 2e, stimulated Dooku1-sensitive insulin release from β-cells and pancreatic islets. Hypotonicity and high glucose increased intracellular Ca2+ and enhanced Yoda1 Ca2+ influx responses. Yoda1 and hypotonicity induced insulin release were significantly inhibited by Piezo1 specific siRNA. Pancreatic islets from mice with haploinsufficiency of Piezo1 released less insulin upon exposure to Yoda1. The data show that Piezo1 channel agonist induces insulin release from β-cell lines and mouse pancreatic islets suggesting a role for Piezo1 in cell swelling induced insulin release. Hence Piezo1 agonists have the potential to be used as enhancers of insulin release.
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Affiliation(s)
- Vijayalakshmi Deivasikamani
- Leeds Institute for Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Savitha Dhayalan
- Leeds Institute for Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Yilizila Abudushalamu
- Leeds Institute for Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Romana Mughal
- Leeds Institute for Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Asjad Visnagri
- Leeds Institute for Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Kevin Cuthbertson
- School of Chemistry, Faculty of Mathematics and Physical Sciences, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Jason L Scragg
- Leeds Institute for Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Tim S Munsey
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Hema Viswambharan
- Leeds Institute for Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Katsuhiko Muraki
- School of Pharmacy, Aichi-Gakuin University, 1-100 Kusumoto, Chikusa, Nagoya, 464-8650, Japan
| | - Richard Foster
- School of Chemistry, Faculty of Mathematics and Physical Sciences, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Asipu Sivaprasadarao
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Mark T Kearney
- Leeds Institute for Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - David J Beech
- Leeds Institute for Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Piruthivi Sukumar
- Leeds Institute for Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, LS2 9JT, United Kingdom.
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Arsenijevic T, Perret J, Van Laethem JL, Delporte C. Aquaporins Involvement in Pancreas Physiology and in Pancreatic Diseases. Int J Mol Sci 2019; 20:E5052. [PMID: 31614661 PMCID: PMC6834120 DOI: 10.3390/ijms20205052] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Revised: 10/10/2019] [Accepted: 10/11/2019] [Indexed: 12/14/2022] Open
Abstract
Aquaporins are a family of transmembrane proteins permeable to water. In mammals, they are subdivided into classical aquaporins that are permeable to water; aquaglyceroporins that are permeable to water, glycerol and urea; peroxiporins that facilitate the diffusion of H2O2 through cell membranes; and so called unorthodox aquaporins. Aquaporins ensure important physiological functions in both exocrine and endocrine pancreas. Indeed, they are involved in pancreatic fluid secretion and insulin secretion. Modification of aquaporin expression and/or subcellular localization may be involved in the pathogenesis of pancreatic insufficiencies, diabetes and pancreatic cancer. Aquaporins may represent useful drug targets for the treatment of pathophysiological conditions affecting pancreatic function, and/or diagnostic/predictive biomarker for pancreatic cancer. This review summarizes the current knowledge related to the involvement of aquaporins in the pancreas physiology and physiopathology.
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Affiliation(s)
- Tatjana Arsenijevic
- Laboratory of Experimental Gastroenterology, Université Libre de Bruxelles, 1070 Brussels, Belgium.
- Department of Gastroenterology, Hepatology and Digestive Oncology, Hôpital Erasme, Université Libre de Bruxelles, 808, Route de Lennik, 1070 Brussels, Belgium.
| | - Jason Perret
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, 1070 Brussels, Belgium.
| | - Jean-Luc Van Laethem
- Laboratory of Experimental Gastroenterology, Université Libre de Bruxelles, 1070 Brussels, Belgium.
- Department of Gastroenterology, Hepatology and Digestive Oncology, Hôpital Erasme, Université Libre de Bruxelles, 808, Route de Lennik, 1070 Brussels, Belgium.
| | - Christine Delporte
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, 1070 Brussels, Belgium.
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Jacobson DA, Shyng SL. Ion Channels of the Islets in Type 2 Diabetes. J Mol Biol 2019; 432:1326-1346. [PMID: 31473158 DOI: 10.1016/j.jmb.2019.08.014] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Revised: 08/19/2019] [Accepted: 08/21/2019] [Indexed: 02/06/2023]
Abstract
Ca2+ is an essential signal for pancreatic β-cell function. Ca2+ plays critical roles in numerous β-cell pathways such as insulin secretion, transcription, metabolism, endoplasmic reticulum function, and the stress response. Therefore, β-cell Ca2+ handling is tightly controlled. At the plasma membrane, Ca2+ entry primarily occurs through voltage-dependent Ca2+ channels. Voltage-dependent Ca2+ channel activity is dependent on orchestrated fluctuations in the plasma membrane potential or voltage, which are mediated via the activity of many ion channels. During the pathogenesis of type 2 diabetes the β-cell is exposed to stressful conditions, which result in alterations of Ca2+ handling. Some of the changes in β-cell Ca2+ handling that occur under stress result from perturbations in ion channel activity, expression or localization. Defective Ca2+ signaling in the diabetic β-cell alters function, limits insulin secretion and exacerbates hyperglycemia. In this review, we focus on the β-cell ion channels that control Ca2+ handling and how they impact β-cell dysfunction in type 2 diabetes.
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Affiliation(s)
- David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, 7415 MRB4 (Langford), 2213 Garland Avenue, Nashville, TN 37232, USA.
| | - Show-Ling Shyng
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, L224, MRB 624, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA.
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15
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Chen L, König B, Liu T, Pervaiz S, Razzaque YS, Stauber T. More than just a pressure relief valve: physiological roles of volume-regulated LRRC8 anion channels. Biol Chem 2019; 400:1481-1496. [DOI: 10.1515/hsz-2019-0189] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Accepted: 04/27/2019] [Indexed: 12/29/2022]
Abstract
Abstract
The volume-regulated anion channel (VRAC) is a key player in the volume regulation of vertebrate cells. This ubiquitously expressed channel opens upon osmotic cell swelling and potentially other cues and releases chloride and organic osmolytes, which contributes to regulatory volume decrease (RVD). A plethora of studies have proposed a wide range of physiological roles for VRAC beyond volume regulation including cell proliferation, differentiation and migration, apoptosis, intercellular communication by direct release of signaling molecules and by supporting the exocytosis of insulin. VRAC was additionally implicated in pathological states such as cancer therapy resistance and excitotoxicity under ischemic conditions. Following extensive investigations, 5 years ago leucine-rich repeat-containing family 8 (LRRC8) heteromers containing LRRC8A were identified as the pore-forming components of VRAC. Since then, molecular biological approaches have allowed further insight into the biophysical properties and structure of VRAC. Heterologous expression, siRNA-mediated downregulation and genome editing in cells, as well as the use of animal models have enabled the assessment of the proposed physiological roles, together with the identification of new functions including spermatogenesis and the uptake of antibiotics and platinum-based cancer drugs. This review discusses the recent molecular biological insights into the physiology of VRAC in relation to its previously proposed roles.
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Affiliation(s)
- Lingye Chen
- Institut für Chemie und Biochemie , Freie Universität Berlin , Thielallee 63 , D-14195 Berlin , Germany
| | - Benjamin König
- Institut für Chemie und Biochemie , Freie Universität Berlin , Thielallee 63 , D-14195 Berlin , Germany
| | - Tianbao Liu
- Institut für Chemie und Biochemie , Freie Universität Berlin , Thielallee 63 , D-14195 Berlin , Germany
| | - Sumaira Pervaiz
- Institut für Chemie und Biochemie , Freie Universität Berlin , Thielallee 63 , D-14195 Berlin , Germany
| | - Yasmin S. Razzaque
- Institut für Chemie und Biochemie , Freie Universität Berlin , Thielallee 63 , D-14195 Berlin , Germany
| | - Tobias Stauber
- Institut für Chemie und Biochemie , Freie Universität Berlin , Thielallee 63 , D-14195 Berlin , Germany
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16
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Sawatani T, Kaneko YK, Doutsu I, Ogawa A, Ishikawa T. TRPV2 channels mediate insulin secretion induced by cell swelling in mouse pancreatic β-cells. Am J Physiol Cell Physiol 2019; 316:C434-C443. [PMID: 30649920 DOI: 10.1152/ajpcell.00210.2017] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
β-Cell swelling induces membrane depolarization, which has been suggested to be caused at least partly by the activation of cation channels. Here, we show the identification of the cation channels. In isolated mouse pancreatic β-cells, the exposure to 30% hypotonic solution elicited an increase in cytosolic Ca2+ concentration ([Ca2+]c). The [Ca2+]c elevation was partially inhibited by ruthenium red, a blocker of several Ca2+-permeable channels including transient receptor potential vanilloid receptors [transient receptor potential cation channel subfamily V (TRPV)], and by nicardipine, but not by the depletion of intracellular Ca2+ stores with thapsigargin and caffeine. The hypotonic stimulation also increased insulin secretion from isolated mouse islets, which was significantly suppressed by ruthenium red. Expression of TRPV2 and TRPV4 was confirmed in mouse pancreatic islets and the MIN6 β-cell line by RT-PCR, Western blot, and immunohistochemical analyses. However, neither 4α-phorbol 12,13-didecanoate nor GSK1016790A, TRPV4 activators, showed any apparent effect on [Ca2+]c in isolated mouse β-cells or in MIN6 cells. In contrast, probenecid, a TRPV2 activator, induced an increase in [Ca2+]c in MIN6 cells, which was attenuated by ruthenium red. Moreover, the [Ca2+]c elevation induced by 30% hypotonic stimulation was significantly reduced by knockdown of TRPV2 with siRNA and by tranilast, a TRPV2 inhibitor. The knockdown of TRPV2 also decreased insulin secretion induced by the hypotonic stimulation. In addition, glucose-stimulated insulin secretion was also significantly reduced in the TRPV2-knockdown MIN6 cells. These results suggest that osmotic cell swelling activates TRPV2 in mouse β-cells, thereby causing membrane depolarization and subsequent activation of voltage-dependent Ca2+ channels and insulin secretion.
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Affiliation(s)
- Toshiaki Sawatani
- Department of Pharmacology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka City, Japan
| | - Yukiko K Kaneko
- Department of Pharmacology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka City, Japan
| | - Isao Doutsu
- Department of Pharmacology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka City, Japan
| | - Ai Ogawa
- Department of Pharmacology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka City, Japan
| | - Tomohisa Ishikawa
- Department of Pharmacology, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka City, Japan
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17
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Osei-Owusu J, Yang J, Vitery MDC, Qiu Z. Molecular Biology and Physiology of Volume-Regulated Anion Channel (VRAC). CURRENT TOPICS IN MEMBRANES 2018; 81:177-203. [PMID: 30243432 DOI: 10.1016/bs.ctm.2018.07.005] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The Volume-Regulated Anion Channel (VRAC) is activated by cell swelling and plays a key role in cell volume regulation. VRAC is ubiquitously expressed in vertebrate cells and also implicated in many other physiological and cellular processes including fluid secretion, glutamate release, membrane potential regulation, cell proliferation, migration, and apoptosis. Although its biophysical properties have been well characterized, the molecular identity of VRAC remained a mystery for almost three decades. The field was transformed by recent discoveries showing that the leucine-rich repeat-containing protein 8A (LRRC8A, also named SWELL1) and its four other homologs form heteromeric VRAC channels. The composition of LRRC8 subunits determines channel properties and substrate selectivity of a large variety of different VRACs. Incorporating purified SWELL1-containing protein complexes into lipid bilayers is sufficient to reconstitute channel activities, a finding that supports the decrease in intracellular ionic strength as the mechanism of VRAC activation during cell swelling. Characterization of Swell1 knockout mice uncovers the important role of VRAC in T cell development, pancreatic β-cell glucose-stimulated insulin secretion, and adipocyte metabolic function. The ability to permeate organic osmolytes and metabolites is a major feature of VRAC. The list of VRAC substrates is expected to grow, now also including some cancer drugs and antibiotics even under non-cell swelling conditions. Therefore, a critical role of VRAC in drug resistance and cell-cell communication is emerging. This review summarizes the exciting recent progress on the structure-function relationship and physiology of VRAC and discusses key future questions to be solved.
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Affiliation(s)
- James Osei-Owusu
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Junhua Yang
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Maria Del Carmen Vitery
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Zhaozhu Qiu
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States; Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, United States
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18
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Calamita G, Perret J, Delporte C. Aquaglyceroporins: Drug Targets for Metabolic Diseases? Front Physiol 2018; 9:851. [PMID: 30042691 PMCID: PMC6048697 DOI: 10.3389/fphys.2018.00851] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Accepted: 06/15/2018] [Indexed: 12/29/2022] Open
Abstract
Aquaporins (AQPs) are a family of transmembrane channel proteins facilitating the transport of water, small solutes, and gasses across biological membranes. AQPs are expressed in all tissues and ensure multiple roles under normal and pathophysiological conditions. Aquaglyceroporins are a subfamily of AQPs permeable to glycerol in addition to water and participate thereby to energy metabolism. This review focalizes on the present knowledge of the expression, regulation and physiological roles of AQPs in adipose tissue, liver and endocrine pancreas, that are involved in energy metabolism. In addition, the review aims at summarizing the involvement of AQPs in metabolic disorders, such as obesity, diabetes and liver diseases. Finally, challenges and recent advances related to pharmacological modulation of AQPs expression and function to control and treat metabolic diseases are discussed.
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Affiliation(s)
- Giuseppe Calamita
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari Aldo Moro, Bari, Italy
| | - Jason Perret
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium
| | - Christine Delporte
- Laboratory of Pathophysiological and Nutritional Biochemistry, Université Libre de Bruxelles, Brussels, Belgium
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19
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da Silva IV, Rodrigues JS, Rebelo I, Miranda JPG, Soveral G. Revisiting the metabolic syndrome: the emerging role of aquaglyceroporins. Cell Mol Life Sci 2018; 75:1973-1988. [PMID: 29464285 PMCID: PMC11105723 DOI: 10.1007/s00018-018-2781-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Revised: 02/05/2018] [Accepted: 02/15/2018] [Indexed: 02/07/2023]
Abstract
The metabolic syndrome (MetS) includes a group of medical conditions such as insulin resistance (IR), dyslipidemia and hypertension, all associated with an increased risk for cardiovascular disease. Increased visceral and ectopic fat deposition are also key features in the development of IR and MetS, with pathophysiological sequels on adipose tissue, liver and muscle. The recent recognition of aquaporins (AQPs) involvement in adipose tissue homeostasis has opened new perspectives for research in this field. The members of the aquaglyceroporin subfamily are specific glycerol channels implicated in energy metabolism by facilitating glycerol outflow from adipose tissue and its systemic distribution and uptake by liver and muscle, unveiling these membrane channels as key players in lipid balance and energy homeostasis. Being involved in a variety of pathophysiological mechanisms including IR and obesity, AQPs are considered promising drug targets that may prompt novel therapeutic approaches for metabolic disorders such as MetS. This review addresses the interplay between adipose tissue, liver and muscle, which is the basis of the metabolic syndrome, and highlights the involvement of aquaglyceroporins in obesity and related pathologies and how their regulation in different organs contributes to the features of the metabolic syndrome.
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Affiliation(s)
- Inês Vieira da Silva
- Faculty of Pharmacy, Research Institute for Medicines (iMed.ULisboa), Universidade de Lisboa, 1649-003, Lisbon, Portugal
- Department of Biochemistry and Human Biology, Faculty of Pharmacy, Universidade de Lisboa, 1649-003, Lisbon, Portugal
| | - Joana S Rodrigues
- Faculty of Pharmacy, Research Institute for Medicines (iMed.ULisboa), Universidade de Lisboa, 1649-003, Lisbon, Portugal
- Department of Toxicological and Bromatological Sciences, Faculty of Pharmacy, Universidade de Lisboa, 1649-003, Lisbon, Portugal
| | - Irene Rebelo
- UCIBIO, REQUIMTE, Department of Biological Sciences, Faculty of Pharmacy, Universidade do Porto, Porto, Portugal
| | - Joana P G Miranda
- Faculty of Pharmacy, Research Institute for Medicines (iMed.ULisboa), Universidade de Lisboa, 1649-003, Lisbon, Portugal
- Department of Toxicological and Bromatological Sciences, Faculty of Pharmacy, Universidade de Lisboa, 1649-003, Lisbon, Portugal
| | - Graça Soveral
- Faculty of Pharmacy, Research Institute for Medicines (iMed.ULisboa), Universidade de Lisboa, 1649-003, Lisbon, Portugal.
- Department of Biochemistry and Human Biology, Faculty of Pharmacy, Universidade de Lisboa, 1649-003, Lisbon, Portugal.
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20
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Stuhlmann T, Planells-Cases R, Jentsch TJ. LRRC8/VRAC anion channels enhance β-cell glucose sensing and insulin secretion. Nat Commun 2018. [PMID: 29773801 DOI: 10.1038/s41467‐018‐04353‐y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Glucose homeostasis depends critically on insulin that is secreted by pancreatic β-cells. Serum glucose, which is directly sensed by β-cells, stimulates depolarization- and Ca2+-dependent exocytosis of insulin granules. Here we show that pancreatic islets prominently express LRRC8A and LRRC8D, subunits of volume-regulated VRAC anion channels. Hypotonicity- or glucose-induced β-cell swelling elicits canonical LRRC8A-dependent VRAC currents that depolarize β-cells to an extent that causes electrical excitation. Glucose-induced excitation and Ca2+ responses are delayed in onset, but not abolished, in β-cells lacking the essential VRAC subunit LRRC8A. Whereas Lrrc8a disruption does not affect tolbutamide- or high-K+-induced insulin secretion from pancreatic islets, it reduces first-phase glucose-induced insulin secretion. Mice lacking VRAC in β-cells have normal resting serum glucose levels but impaired glucose tolerance. We propose that opening of LRRC8/VRAC channels increases glucose sensitivity and insulin secretion of β-cells synergistically with KATP closure. Neurotransmitter-permeable LRRC8D-containing VRACs might have additional roles in autocrine/paracrine signaling within islets.
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Affiliation(s)
- Till Stuhlmann
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Robert-Rössle-Strasse 10, 13125, Berlin, Germany.,Graduate Program of the Faculty for Biology, Chemistry and Pharmacy, Freie Universität Berlin, 14195 Berlin, Germany
| | - Rosa Planells-Cases
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Robert-Rössle-Strasse 10, 13125, Berlin, Germany
| | - Thomas J Jentsch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Robert-Rössle-Strasse 10, 13125, Berlin, Germany. .,Neurocure Cluster of Excellence, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany.
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21
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Stuhlmann T, Planells-Cases R, Jentsch TJ. LRRC8/VRAC anion channels enhance β-cell glucose sensing and insulin secretion. Nat Commun 2018; 9:1974. [PMID: 29773801 PMCID: PMC5958052 DOI: 10.1038/s41467-018-04353-y] [Citation(s) in RCA: 67] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 04/23/2018] [Indexed: 01/09/2023] Open
Abstract
Glucose homeostasis depends critically on insulin that is secreted by pancreatic β-cells. Serum glucose, which is directly sensed by β-cells, stimulates depolarization- and Ca2+-dependent exocytosis of insulin granules. Here we show that pancreatic islets prominently express LRRC8A and LRRC8D, subunits of volume-regulated VRAC anion channels. Hypotonicity- or glucose-induced β-cell swelling elicits canonical LRRC8A-dependent VRAC currents that depolarize β-cells to an extent that causes electrical excitation. Glucose-induced excitation and Ca2+ responses are delayed in onset, but not abolished, in β-cells lacking the essential VRAC subunit LRRC8A. Whereas Lrrc8a disruption does not affect tolbutamide- or high-K+-induced insulin secretion from pancreatic islets, it reduces first-phase glucose-induced insulin secretion. Mice lacking VRAC in β-cells have normal resting serum glucose levels but impaired glucose tolerance. We propose that opening of LRRC8/VRAC channels increases glucose sensitivity and insulin secretion of β-cells synergistically with KATP closure. Neurotransmitter-permeable LRRC8D-containing VRACs might have additional roles in autocrine/paracrine signaling within islets.
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Affiliation(s)
- Till Stuhlmann
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Robert-Rössle-Strasse 10, 13125, Berlin, Germany.,Graduate Program of the Faculty for Biology, Chemistry and Pharmacy, Freie Universität Berlin, 14195 Berlin, Germany
| | - Rosa Planells-Cases
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Robert-Rössle-Strasse 10, 13125, Berlin, Germany
| | - Thomas J Jentsch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Robert-Rössle-Strasse 10, 13125, Berlin, Germany. .,Neurocure Cluster of Excellence, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany.
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22
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Rashid CS, Lien YC, Bansal A, Jaeckle-Santos LJ, Li C, Won KJ, Simmons RA. Transcriptomic Analysis Reveals Novel Mechanisms Mediating Islet Dysfunction in the Intrauterine Growth-Restricted Rat. Endocrinology 2018; 159:1035-1049. [PMID: 29309562 PMCID: PMC5793792 DOI: 10.1210/en.2017-00888] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Accepted: 12/28/2017] [Indexed: 02/07/2023]
Abstract
Intrauterine growth restriction (IUGR) increases the risk of type 2 diabetes developing in adulthood. In previous studies that used bilateral uterine artery ligation in a rat model of IUGR, age-associated decline in glucose homeostasis and islet function was revealed. To elucidate mechanisms contributing to IUGR pathogenesis, the islet transcriptome was sequenced from 2-week-old rats, when in vivo glucose tolerance is mildly impaired, and at 10 weeks of age, when rats are hyperglycemic and have reduced β-cell mass. RNA sequencing and functional annotation with Ingenuity Pathway Analysis revealed temporal changes in IUGR islets. For instance, gene expression involving amino acid metabolism was significantly reduced primarily at 2 weeks of age, but ion channel expression, specifically that involved in cell-volume regulation, was more disrupted in adult IUGR islets. Additionally, we observed alterations in the microenvironment of IUGR islets with extracellular matrix genes being significantly increased at 2 weeks of age and significantly decreased at 10 weeks. Specifically, hyaluronan synthase 2 expression and hyaluronan staining were increased in IUGR islets at 2 weeks of age (P < 0.05). Mesenchymal stromal cell-derived factors that have been shown to preserve islet allograft function, such as Anxa1, Cxcl12, and others, also were increased at 2 weeks and decreased in adult islets. Finally, comparisons of differentially expressed genes with those of type 2 diabetic human islets support a role for these pathways in human patients with diabetes. Together, these data point to new mechanisms in the pathogenesis of IUGR-mediated islet dysfunction in type 2 diabetes.
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Affiliation(s)
- Cetewayo S. Rashid
- Center for Research on Reproduction and Women’s Health, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
- Division of Neonatology, Department of Pediatrics, The Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
| | - Yu-Chin Lien
- Center for Research on Reproduction and Women’s Health, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Amita Bansal
- Center for Research on Reproduction and Women’s Health, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
- Division of Neonatology, Department of Pediatrics, The Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
| | - Lane J. Jaeckle-Santos
- Division of Neonatology, Department of Pediatrics, The Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
| | - Changhong Li
- Division of Endocrinology and Diabetes, The Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
- Institute for Diabetes, Obesity, and Metabolism, Smilow Center for Translational Research, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Kyoung-Jae Won
- Institute for Diabetes, Obesity, and Metabolism, Smilow Center for Translational Research, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
- Department of Genetics, Smilow Center for Translational Research, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Rebecca A. Simmons
- Center for Research on Reproduction and Women’s Health, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
- Division of Neonatology, Department of Pediatrics, The Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania 19104
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23
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Abstract
Insulin secretion is initiated by activation of voltage-gated Ca2+ channels (VGCC) to trigger Ca2+-mediated insulin vesicle fusion with the β-cell plasma membrane. The firing of VGCC requires β-cell membrane depolarization, which is regulated by a balance of depolarizing and hyperpolarizing ionic currents. Here, we show that SWELL1 mediates a swell-activated, depolarizing chloride current (ICl,SWELL) in both murine and human β-cells. Hypotonic and glucose-stimulated β-cell swelling activates SWELL1-mediated ICl,SWELL and this contributes to membrane depolarization and activation of VGCC-dependent intracellular calcium signaling. SWELL1 depletion in MIN6 cells and islets significantly impairs glucose-stimulated insulin secretion. Tamoxifen-inducible β-cell-targeted Swell1 KO mice have normal fasting serum glucose and insulin levels but impaired glucose-stimulated insulin secretion and glucose tolerance; and this is further exacerbated in mild obesity. Our results reveal that β-cell SWELL1 modulates insulin secretion and systemic glycaemia by linking glucose-mediated β-cell swelling to membrane depolarization and activation of VGCC-triggered calcium signaling.
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24
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Kang C, Xie L, Gunasekar SK, Mishra A, Zhang Y, Pai S, Gao Y, Kumar A, Norris AW, Stephens SB, Sah R. SWELL1 is a glucose sensor regulating β-cell excitability and systemic glycaemia. Nat Commun 2018; 9:367. [PMID: 29371604 PMCID: PMC5785485 DOI: 10.1038/s41467-017-02664-0] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2017] [Accepted: 12/15/2017] [Indexed: 12/11/2022] Open
Abstract
Insulin secretion is initiated by activation of voltage-gated Ca2+ channels (VGCC) to trigger Ca2+-mediated insulin vesicle fusion with the β-cell plasma membrane. The firing of VGCC requires β-cell membrane depolarization, which is regulated by a balance of depolarizing and hyperpolarizing ionic currents. Here, we show that SWELL1 mediates a swell-activated, depolarizing chloride current (ICl,SWELL) in both murine and human β-cells. Hypotonic and glucose-stimulated β-cell swelling activates SWELL1-mediated ICl,SWELL and this contributes to membrane depolarization and activation of VGCC-dependent intracellular calcium signaling. SWELL1 depletion in MIN6 cells and islets significantly impairs glucose-stimulated insulin secretion. Tamoxifen-inducible β-cell-targeted Swell1 KO mice have normal fasting serum glucose and insulin levels but impaired glucose-stimulated insulin secretion and glucose tolerance; and this is further exacerbated in mild obesity. Our results reveal that β-cell SWELL1 modulates insulin secretion and systemic glycaemia by linking glucose-mediated β-cell swelling to membrane depolarization and activation of VGCC-triggered calcium signaling.
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Affiliation(s)
- Chen Kang
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of Iowa, Carver College of Medicine, Iowa City, IA, 52242, USA
| | - Litao Xie
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of Iowa, Carver College of Medicine, Iowa City, IA, 52242, USA
| | - Susheel K Gunasekar
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of Iowa, Carver College of Medicine, Iowa City, IA, 52242, USA
| | - Anil Mishra
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of Iowa, Carver College of Medicine, Iowa City, IA, 52242, USA
| | - Yanhui Zhang
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of Iowa, Carver College of Medicine, Iowa City, IA, 52242, USA
| | - Saachi Pai
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of Iowa, Carver College of Medicine, Iowa City, IA, 52242, USA
| | - Yiwen Gao
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of Iowa, Carver College of Medicine, Iowa City, IA, 52242, USA
| | - Ashutosh Kumar
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of Iowa, Carver College of Medicine, Iowa City, IA, 52242, USA
| | - Andrew W Norris
- Department of Pediatrics, University of Iowa, Carver College of Medicine, Iowa City, IA, 52242, USA
- Fraternal Order of the Eagles Diabetes Research Center, Iowa City, IA, 52242, USA
| | - Samuel B Stephens
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of Iowa, Carver College of Medicine, Iowa City, IA, 52242, USA
- Fraternal Order of the Eagles Diabetes Research Center, Iowa City, IA, 52242, USA
| | - Rajan Sah
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of Iowa, Carver College of Medicine, Iowa City, IA, 52242, USA.
- Fraternal Order of the Eagles Diabetes Research Center, Iowa City, IA, 52242, USA.
- Abboud Cardiovascular Research Center, University of Iowa Carver College of Medicine, Iowa City, IA, 52242, USA.
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25
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Abstract
Aquaporins (AQPs ) are expressed in most exocrine and endocrine secretory glands. Consequently, summarizing the expression and functions of AQPs in secretory glands represents a daunting task considering the important number of glands present in the body, as well as the number of mammalian AQPs - thirteen. The roles played by AQPs in secretory processes have been investigated in many secretory glands. However, despite considerable research, additional studies are clearly needed to pursue our understanding of the role played by AQPs in secretory processes. This book chapter will focus on summarizing the current knowledge on AQPs expression and function in the gastrointestinal tract , including salivary glands, gastric glands, Duodenal Brunner's gland, liver and gallbladder, intestinal goblets cells, exocrine and endocrine pancreas, as well as few other secretory glands including airway submucosal glands, lacrimal glands, mammary glands and eccrine sweat glands.
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Affiliation(s)
- Christine Delporte
- Laboratory of Pathophysiological and Nutritional Biochemistry, Faculty of Medicine, Université Libre de Bruxelles, Brussels, Belgium.
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26
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Jentsch TJ. VRACs and other ion channels and transporters in the regulation of cell volume and beyond. Nat Rev Mol Cell Biol 2016; 17:293-307. [PMID: 27033257 DOI: 10.1038/nrm.2016.29] [Citation(s) in RCA: 217] [Impact Index Per Article: 27.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Cells need to regulate their volume to counteract osmotic swelling or shrinkage, as well as during cell division, growth, migration and cell death. Mammalian cells adjust their volume by transporting potassium, sodium, chloride and small organic osmolytes using plasma membrane channels and transporters. This generates osmotic gradients, which drive water in and out of cells. Key players in this process are volume-regulated anion channels (VRACs), the composition of which has recently been identified and shown to encompass LRRC8 heteromers. VRACs also transport metabolites and drugs and function in extracellular signal transduction, apoptosis and anticancer drug resistance.
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Affiliation(s)
- Thomas J Jentsch
- Leibniz-Institut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Robert-Rössle-Strasse 10, 13125 Berlin, Germany
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Abstract
Hypoglycemia in the pediatric population is a common finding important to recognize and manage to prevent brain injury. Recent advances in molecular genetics have provided new insight into its biochemical and physiologic basis and have led to more appropriate and specific treatment. Although a major cause of brain injury in pediatrics, the ability to predict the long-term outcome in these patients remains difficult. Identification of these at-risk individuals is important. The physiologic adaptations associated with transition from fetal to neonatal life are now better understood thus allowing for improved surveillance and management. Despite these advances, analytical limitations of point-of-care testing instruments at low glucose concentration continue to persist, This review aims to address these questions and provide an overview of pediatric hypoglycemia and the molecular pathways involved.
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Aquaporins in salivary glands and pancreas. Biochim Biophys Acta Gen Subj 2014; 1840:1524-32. [DOI: 10.1016/j.bbagen.2013.08.007] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2013] [Revised: 08/07/2013] [Accepted: 08/08/2013] [Indexed: 12/23/2022]
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Effects of octane derivatives on activity of the volume-regulated anion channel in rat pancreatic β-cells. Pharmacol Rep 2014; 65:1317-21. [PMID: 24399728 DOI: 10.1016/s1734-1140(13)71490-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Revised: 06/11/2013] [Indexed: 01/24/2023]
Abstract
BACKGROUND Saturated free fatty acids (FFAs) have a dual action on pancreatic β-cells, consisting of an initial enhancement and subsequent suppression of glucose-induced electrical activity and insulin release. These stimulatory and inhibitory effects have been attributed, at least in part, to the activation and inhibition, respectively, of the volume-regulated anion channel (VRAC) by FFAs. Both effects were independent of their metabolism. We have now investigated the effects of related aliphatic compounds in order to further define the determinants of FFA interaction with VRAC. METHODS β-Cell VRAC and electrical activity were measured by conventional whole-cell and perforated patch recording, respectively. Cell volume was measured using a video-imaging technique. RESULTS In common with octanoic acid, addition of methyl octanoate or n-octanol resulted in a rapid, pronounced and reversible inhibition of VRAC activity. Addition of n-octane had no significant effect on VRAC activity. n-Octanol had a biphasic effect on β-cell membrane potential, namely a small transient depolarization followed by a marked hyperpolarization. n-Octanol was also found to prevent regulatory volume decrease in cells exposed to a hypotonic medium, consistent with VRAC inhibition. CONCLUSION It is suggested that methyl octanoate and n-octanol can mimic the effects of FFAs on the pancreatic β-cell via modulation of VRAC activity. The structural requirements for this effect appear to be a medium or long chain aliphatic compound containing at least one oxygen atom.
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Louchami K, Best L, Brown P, Virreira M, Hupkens E, Perret J, Devuyst O, Uchida S, Delporte C, Malaisse WJ, Beauwens R, Sener A. A new role for aquaporin 7 in insulin secretion. Cell Physiol Biochem 2012; 29:65-74. [PMID: 22415076 DOI: 10.1159/000337588] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/16/2011] [Indexed: 11/19/2022] Open
Abstract
UNLABELLED BACGROUNS/AIMS: Several insulinotropic agents were recently reported to cause β-cell swelling. The possible participation of AQP7 to water transport was investigated in AQP7(+/+) or AQP7(-/-) mice. METHODS Aquaporin expression, insulin secretion, cell swelling and electrical activity were investigated in pancreatic islets. RESULTS RT-PCR revealed the expression of AQP5 and AQP8 mRNA. Double immunofluorescent labeling indicated their presence in β-cells. Whilst basal insulin release from isolated pancreatic islets incubated at 2.8 mM D-glucose did not differ between AQP7(+/+) or AQP7(-/-) mice, the secretion of insulin evoked by the omission of 50 mM NaCl, the substitution of 50 mM NaCl by 100 mM glycerol or a rise in D-glucose concentration to 8.3 mM and 16.7 mM was severely impaired in the islets from AQP7(-/-) mice. Yet, exposure of β-cells to either the hypotonic medium or a rise in D-glucose concentration caused a similar degree of swelling and comparable pattern of electrical activity in cells from AQP7(+/+) and AQP7(-/-) mice. Both the cell swelling and change in membrane potential were only impaired in AQP7(-/-) cells when exposed to 50 mM glycerol. CONCLUSION It is proposed, therefore, that AQP7 may, directly or indirectly, play a role at a distal site in the exocytotic pathway.
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Affiliation(s)
- Karim Louchami
- Laboratory of Experimental Hormonology, Université Libre de Bruxelles, Brussels, Belgium
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Belkacemi L, Selselet-Attou G, Hupkens E, Nguidjoe E, Louchami K, Sener A, Malaisse WJ. Intermittent fasting modulation of the diabetic syndrome in streptozotocin-injected rats. Int J Endocrinol 2012; 2012:962012. [PMID: 22291702 PMCID: PMC3265126 DOI: 10.1155/2012/962012] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/26/2011] [Revised: 10/09/2011] [Accepted: 10/13/2011] [Indexed: 11/18/2022] Open
Abstract
This study investigates the effects of intermittent overnight fasting in streptozotocin-induced diabetic rats (STZ rats). Over 30 days, groups of 5-6 control or STZ rats were allowed free food access, starved overnight, or exposed to a restricted food supply comparable to that ingested by the intermittently fasting animals. Intermittent fasting improved glucose tolerance, increased plasma insulin, and lowered Homeostatis Model Assessment index. Caloric restriction failed to cause such beneficial effects. The β-cell mass, as well as individual β-cell and islet area, was higher in intermittently fasting than in nonfasting STZ rats, whilst the percentage of apoptotic β-cells appeared lower in the former than latter STZ rats. In the calorie-restricted STZ rats, comparable findings were restricted to individual islet area and percentage of apoptotic cells. Hence, it is proposed that intermittent fasting could represent a possible approach to prevent or minimize disturbances of glucose homeostasis in human subjects.
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Affiliation(s)
- Louiza Belkacemi
- Laboratoire de Technologie Alimentaire et Nutrition, Université de Mostaganem, 1070 Mostaganem, Algeria
| | - Ghalem Selselet-Attou
- Laboratoire de Technologie Alimentaire et Nutrition, Université de Mostaganem, 1070 Mostaganem, Algeria
| | - Emeline Hupkens
- Laboratory of Experimental Hormonology, Université Libre de Bruxelles, 808 Route de Lennik, 1070 Brussels, Belgium
| | - Evrard Nguidjoe
- Laboratory of Pharmacology, Université Libre de Bruxelles, 808 Route de Lennik, 1070 Brussels, Belgium
| | - Karim Louchami
- Laboratory of Experimental Hormonology, Université Libre de Bruxelles, 808 Route de Lennik, 1070 Brussels, Belgium
| | - Abdullah Sener
- Laboratory of Experimental Hormonology, Université Libre de Bruxelles, 808 Route de Lennik, 1070 Brussels, Belgium
| | - Willy J. Malaisse
- Laboratory of Experimental Hormonology, Université Libre de Bruxelles, 808 Route de Lennik, 1070 Brussels, Belgium
- *Willy J. Malaisse:
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Crutzen R, Shlyonsky V, Louchami K, Virreira M, Hupkens E, Boom A, Sener A, Malaisse WJ, Beauwens R. Does NAD(P)H oxidase-derived H2O2 participate in hypotonicity-induced insulin release by activating VRAC in β-cells? Pflugers Arch 2011; 463:377-90. [PMID: 22089811 DOI: 10.1007/s00424-011-1047-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Revised: 10/14/2011] [Accepted: 10/17/2011] [Indexed: 01/12/2023]
Abstract
NAD(P)H oxidase (NOX)-derived H(2)O(2) was recently proposed to act, in several cells, as the signal mediating the activation of volume-regulated anion channels (VRAC) under a variety of physiological conditions. The present study aims at investigating whether a similar situation prevails in insulin-secreting BRIN-BD11 and rat β-cells. Exogenous H(2)O(2) (100 to 200 μM) at basal glucose concentration (1.1 to 2.8 mM) stimulated insulin secretion. The inhibitor of VRAC, 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) inhibited the secretory response to exogenous H(2)O(2). In patch clamp experiments, exogenous H(2)O(2) was observed to stimulate NPPB-sensitive anion channel activity, which induced cell membrane depolarization. Exposure of the BRIN-BD11 cells to a hypotonic medium caused a detectable increase in intracellular level of reactive oxygen species (ROS) that was abolished by diphenyleneiodonium chloride (DPI), a universal NOX inhibitor. NOX inhibitors such as DPI and plumbagin nearly totally inhibited insulin release provoked by exposure of the BRIN-BD11 cells to a hypotonic medium. Preincubation with two other drugs also abolished hypotonicity-induced insulin release and reduced basal insulin output: 1) N-acetyl-L-cysteine (NAC), a glutathione precursor that serves as general antioxidant and 2) betulinic acid a compound that almost totally abolished NOX4 expression. As NPPB, each of these inhibitors (DPI, plumbagin, preincubation with NAC or betulinic acid) strongly reduced the volume regulatory decrease observed following a hypotonic shock, providing an independent proof that VRAC activation is mediated by H(2)O(2). Taken together, these data suggest that NOX-derived H(2)O(2) plays a key role in the insulin secretory response of BRIN-BD11 and native β-cells to extracellular hypotonicity.
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Affiliation(s)
- R Crutzen
- Laboratory of Cell and Molecular Physiology, Université Libre de Bruxelles, Campus Erasme, CP 611. Room E1.6.214, Route de Lennik, 808, 1070, Bruxelles, Belgium
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McGlasson L, Best L, Brown PD. The glucokinase activator GKA50 causes an increase in cell volume and activation of volume-regulated anion channels in rat pancreatic β-cells. Mol Cell Endocrinol 2011; 342:48-53. [PMID: 21664426 DOI: 10.1016/j.mce.2011.05.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/31/2010] [Revised: 05/06/2011] [Accepted: 05/22/2011] [Indexed: 10/18/2022]
Abstract
Glucokinase plays a key role in the metabolism of glucose by pancreatic β-cells. In this study the effects of the glucokinase activator GKA50 on cell volume and electrical activity in rat β-cells were examined. One micro molar GKA50 caused an increase in β-cell volume in the presence of 4mM glucose. GKA50 also caused a depolarisation of β-cell membrane potential and increased electrical activity. These changes were associated with the activation of inward whole-cell currents, and were attenuated by the anion channel inhibitor 5-nitro-2-(3-phenylpropylamino) benzoic acid. In single channel experiments, the open probability of volume-regulated anion channels (VRAC) was increased from 0.03±0.01 to 0.19±0.04 (n=3) by the GKA50. The data suggest that a GKA50-evoked increase in glucose metabolism causes an increase in β-cell volume. This in turn activates VRAC leading to a depolarisation of the cell membrane potential.
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Affiliation(s)
- Lisa McGlasson
- Faculty of Life Sciences and Medicine, University of Manchester, Manchester M13 9NT, UK
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Best L, Jarman E, Brown PD. A dual action of saturated fatty acids on electrical activity in rat pancreatic β-cells. Role of volume-regulated anion channel and KATP channel currents. J Physiol 2011; 589:1307-16. [PMID: 21242256 DOI: 10.1113/jphysiol.2010.200741] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Free fatty acids (FFAs) exert complex actions on pancreatic β-cells. Typically, an initial potentiation of insulin release is followed by a gradual impairment of β-cell function, the latter effect being of possible relevance to hyperlipidaemia in type 2 diabetes mellitus. The molecular actions of FFAs are poorly understood. The present study investigated the acute effects of saturated FFAs on electrophysiological responses of rat pancreatic β-cells. Membrane potential and KATP channel activity were recorded using the perforated patch technique. Volume-regulated anion channel (VRAC) activity was assessed from conventional whole-cell recordings. Cell volume regulation was measured using a video-imaging technique. Addition of octanoate caused a transient potentiation of glucose-induced electrical activity, followed by a gradual hyper-polarisation and a prolonged inhibition of electrical activity. Octanoate caused an initial increase in VRAC activity followed by a secondary inhibition coinciding with increased KATP channel activity. Similar effects were observed with palmitate and 2-bromopalmitate whereas butyrate was virtually ineffective. Octanoate and palmitate also exerted a dual effect on electrical activity evoked by tolbutamide. Octanoate significantly attenuated cell volume regulation in hypotonic solutions, consistent with VRAC inhibition. It is concluded that medium and long chain FFAs have a dual action on glucose-induced electrical activity in rat pancreatic β-cells: an initial stimulatory effect followed by a secondary inhibition. These effects appear to be the result of reciprocal actions on VRAC and KATP channel currents, and could contribute towards the stimulatory and inhibitory actions of FFAs on pancreatic β-cell function.
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Affiliation(s)
- L Best
- Schools of Biomedicine, University of Manchester, Manchester, UK.
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Uchida K, Tominaga M. The role of thermosensitive TRP (transient receptor potential) channels in insulin secretion. Endocr J 2011; 58:1021-8. [PMID: 21785227 DOI: 10.1507/endocrj.ej11-0130] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Insulin secretion from pancreatic β-cells is the only efficient means to decrease blood glucose concentrations. Glucose is the principal stimulator of insulin secretion with the ATP-sensitive K+ channel-voltage-gated Ca2+ channel-mediated pathway being the primary one involved in glucose-stimulated insulin secretion. Recently, several reports demonstrated that some transient receptor potential (TRP) channels are expressed in pancreatic β-cells and contribute to pancreatic β-cell functions. Interestingly, six of them (TRPM2, TRPM4, TRPM5, TRPV1, TRPV2 and TRPV4) are thermosensitive TRP channels. Thermosensitive TRP channels in pancreatic β-cells can function as multimodal receptors and cause Ca2+ influx and membrane depolarization at physiological body temperature. TRPM channels (TRPM2, TRPM4 and TRPM5) control insulin secretion levels by sensing intracellular Ca2+ increase, NAD metabolites, or hormone receptor activation. TRPV2 is involved not only in insulin secretion but also cell proliferation, and is regulated by the autocrine effects of insulin. TRPV1 expressed in sensory neurons is involved in β-cell stress and islet inflammation by controlling neuropeptide release levels. It is thus clear that thermosensitive TRP channels play important roles in pancreatic β-cell functions, and future analyses of TRP channel function will lead to better understanding of the complicated mechanisms involved in insulin secretion and diabetes pathogenesis.
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Affiliation(s)
- Kunitoshi Uchida
- Division of Cell Signaling, Okazaki Institute for Integrative Bioscience (National Institute for Physiological Sciences), National Institutes of Natural Sciences, Aichi 444-8787 Japan.
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37
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Štrbák V. Cell Swelling-induced Peptide Hormone Secretion. Cell Physiol Biochem 2011; 28:1155-68. [DOI: 10.1159/000335849] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/09/2011] [Indexed: 11/19/2022] Open
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Hughes AL, Pakhomova A, Brown PD. Regulatory volume increase in epithelial cells isolated from the mouse fourth ventricle choroid plexus involves Na+–H+ exchange but not Na+–K+–2Cl− cotransport. Brain Res 2010; 1323:1-10. [DOI: 10.1016/j.brainres.2009.12.094] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2009] [Revised: 12/03/2009] [Accepted: 12/20/2009] [Indexed: 10/19/2022]
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Best L, Brown PD, Sener A, Malaisse WJ. Opposing effects of tenidap on the volume-regulated anion channel and K(ATP) channel activity in rat pancreatic beta-cells. Eur J Pharmacol 2009; 629:159-63. [PMID: 20035738 DOI: 10.1016/j.ejphar.2009.12.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2009] [Revised: 12/03/2009] [Accepted: 12/15/2009] [Indexed: 11/29/2022]
Abstract
Tenidap (5-chloro-2-hydroxy-3-(thiophene-2-carbonyl)indole-1-carboxamide) is a non-steroidal anti-inflammatory and anti-rheumatic drug with several cellular actions including inhibition of anion transport processes. Since other anion transport inhibitors have been shown to inhibit activity of the volume-regulated anion channel (VRAC), the present study investigated the effects of tenidap on activity of this channel in pancreatic beta-cells. Membrane potential, VRAC currents and input conductance were recorded from single rat beta-cells in primary culture using perforated patch, conventional whole-cell and cell-attached configurations of the patch-clamp technique. Relative cell volume was measured using a video-imaging method. Tenidap (0.1mM) was found to rapidly hyperpolarise the beta-cell membrane potential and terminate glucose-induced electrical activity. This effect was associated with a pronounced outward current shift at a holding potential of -65mV. Tenidap was found to inhibit activity of the volume-regulated anion channel with IC(50) values of 31 and 43microM for outward and inward currents respectively. Tenidap also markedly increased beta-cell input conductance, representing an activation of the K(ATP) conductance. beta-cell regulatory volume decrease following hypotonically-induced cell swelling was sensitive to inhibition by 50microM tenidap. Tenidap is a potent inhibitor of the volume-regulated anion channel and K(ATP) channel activator in rat pancreatic beta-cells. These actions could at least in part explain the recently reported inhibitory actions of the drug on electrical and secretory activity in the beta-cell, and could also underlie other pharmacological actions of the drug.
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Affiliation(s)
- Leonard Best
- Schools of Medicine, University of Manchester, UK.
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Best L, Brown PD. Studies of the mechanism of activation of the volume-regulated anion channel in rat pancreatic beta-cells. J Membr Biol 2009; 230:83-91. [PMID: 19669073 DOI: 10.1007/s00232-009-9189-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2009] [Accepted: 07/13/2009] [Indexed: 11/26/2022]
Abstract
There is evidence that depolarization of the pancreatic beta cell by glucose involves cell swelling and activation of the volume-regulated anion channel (VRAC). However, it is unclear whether cell swelling per se or accompanying changes in intracellular osmolality and/or ionic strength are responsible for VRAC activation. VRAC activity was measured in rat beta cells by conventional or perforated patch whole-cell recording. Cell volume was measured by video imaging. In conventional whole-cell recordings, VRAC activation was achieved by exposure of the cells to a hyposmotic bath solution, by application of positive pressure to the pipette, or by use of a hyperosmotic pipette solution. Increased concentrations of intracellular CsCl also caused channel activation, but with delayed kinetics. In perforated patch recordings, VRAC activation was induced by isosmotic addition of the permeable osmolytes urea, 3-O-methyl glucose, arginine, and NH4Cl. These effects were all accompanied by beta-cell swelling. It is concluded that increased cell volume, whether accompanied by raised intracellular osmolality or ionic strength, is a major determinant of VRAC activation in the beta cell. However, increased intracellular ionic strength markedly reduced the rate of VRAC activation. These findings are consistent with the hypothesis that the accumulation of glucose metabolites in the beta cell, and the resultant increase in cell volume, provides a signal coupling glucose metabolism with VRAC activation.
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Affiliation(s)
- Len Best
- School of Medicine, Manchester Royal Infirmary, University of Manchester, Oxford Road, Manchester M139WL, UK.
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Abstract
Noninvasive imaging and quantification of pancreatic, insulin-producing beta cells has been considered a high-priority field of investigation for the past decade. In the first review on this issue, attention was already paid to various agents for labeling beta cells, including 6-(125)I-D-glucose, (65)Zn, (3)H-glibenclamide, (3)H-mitiglinide, an (125)I-labeled mouse monoclonal antibody against beta-cell surface ganglioside(s), D-(U-(14)C)-glucose and 2-deoxy-2-(18)F-D-glucose to label glycogen accumulated in beta cells in response to sustained hyperglycemia, and, last but not least, an analog of D-mannoheptulose. This Review discusses these methods and further contributions. For instance, emphasis is placed on labeling beta cells with (11)C-dihydrotetrabenazine, which is the most advanced method at present. Attention is also drawn to the latest approaches for noninvasive imaging and functional characterization of pancreatic beta cells. None of these procedures is used in clinical practice yet.
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Zimliki CL, Chenault VM, Mears D. Glucose-dependent and -independent electrical activity in islets of Langerhans of Psammomys obesus, an animal model of nutritionally induced obesity and diabetes. Gen Comp Endocrinol 2009; 161:193-201. [PMID: 19167400 DOI: 10.1016/j.ygcen.2008.12.017] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Revised: 12/17/2008] [Accepted: 12/18/2008] [Indexed: 11/24/2022]
Abstract
Glucose-induced insulin secretion from pancreatic beta-cells involves metabolism-induced membrane depolarization and voltage-dependent Ca(2+) influx. The electrical events in beta-cell glucose sensing have been studied intensely using mouse islets of Langerhans, but data from other species, including models of type 2 diabetes mellitus (T2DM), are lacking. In this work, we made intracellular recordings of electrical activity from cells within islets of the gerbil Psammomys obesus (fat sand rat), a model of dietary-induced T2DM. Most islet cells from lean, non-diabetic sand rats displayed glucose-induced, K(ATP) channel-dependent, oscillatory electrical activity that was similar to the classic "bursting" pattern of mouse beta-cells. However, the oscillations were slower in sand rat islets, and the dose-response curve of electrical activity versus glucose concentration was left-shifted. Of the non-bursting cells, some produced action potentials continuously, while others displayed electrical activity that was largely independent of glucose. The latter activity consisted of continuous or intermittent action potential firing, and persisted for long periods in the absence of glucose. The glucose-insensitive activity was suppressed by diazoxide, indicating that the cells expressed K(ATP) channels. Sand rat islets produced intracellular Ca(2+) oscillations reminiscent of the oscillatory electrical pattern observed in most cells, albeit with a longer period. Finally, we found that the glucose dependence of insulin secretion from sand rat islets closely paralleled that of the bursting electrical activity. We conclude that while subpopulations of K(ATP)-expressing cells in sand rat islets display heterogeneous electrical responses to glucose, insulin secretion most closely follows the oscillatory activity. The ease of recording membrane potential from sand rat islets makes this a useful model for studies of beta-cell electrical signaling during the development of T2DM.
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Affiliation(s)
- Charles L Zimliki
- Department of Anatomy, Physiology & Genetics, Uniformed Services University School of Medicine, Bethesda, MD 20814, USA
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Davies SL, Best L, Brown PD. HCO 3--dependent volume regulation in alpha-cells of the rat endocrine pancreas. Pflugers Arch 2009; 458:621-9. [PMID: 19214560 PMCID: PMC2691524 DOI: 10.1007/s00424-009-0644-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2008] [Revised: 01/21/2009] [Accepted: 01/27/2009] [Indexed: 11/05/2022]
Abstract
Ion transport activity in pancreatic α-cells was assessed by studying cell volume regulation in response to anisotonic solutions. Cell volume was measured by a video imaging method, and cells were superfused with either 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid-buffered or HCO3−-buffered solutions. α-Cells did not exhibit a regulatory volume increase (RVI) in response to cell shrinkage caused by hypertonic solutions. A RVI was observed, however, in cells that had first undergone a regulatory volume decrease (RVD), but only in HCO3−-buffered solutions. RVI was also observed in response to a HCO3−-buffered hypertonic solution in which the glucose concentration was increased from 4 to 20 mM. The post-RVD RVI and the glucose-induced RVI were both inhibited by 10 μM 5-(N-methyl-N-isobutyl) amiloride or 100 μM 2,2′-(1,2-ethenediyl) bis (5-isothio-cyanatobenzenesulfonic acid), but not by 10 μM benzamil nor 10 μM bumetanide. These data suggest that Na+–H+ exchangers and Cl−–HCO3− exchangers contribute to volume regulation in α-cells.
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Affiliation(s)
- Sarah L Davies
- Faculty of Life Sciences, University of Manchester, Second Floor CTF Building, Manchester, M13 9NT, UK
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Randall CL, Leong TG, Bassik N, Gracias DH. 3D lithographically fabricated nanoliter containers for drug delivery. Adv Drug Deliv Rev 2007; 59:1547-61. [PMID: 17919768 DOI: 10.1016/j.addr.2007.08.024] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2007] [Accepted: 08/26/2007] [Indexed: 11/16/2022]
Abstract
Lithographic patterning offers the possibility for precise structuring of drug delivery devices. The fabrication process can also facilitate the incorporation of advanced functionality for imaging, sensing, telemetry and actuation. However, a major limitation of present day lithographic fabrication is the inherent two-dimensionality of the patterning process. We review a new approach to construct three dimensional (3D) patterned containers by lithographically patterning two dimensional (2D) templates with liquefiable hinges that spontaneously fold upon heating into hollow polyhedral containers. The containers have finite encapsulation volumes, can be made small enough to pass through a hypodermic needle, and the 3D profile of the containers facilitates enhanced diffusion with the surrounding medium as compared to reservoir systems fabricated in planar substrates. We compare the features of the containers to those of present day drug delivery systems. These features include ease of manufacture, versatility in size and shape, monodisperse porosity, ability for spatial manipulation and remote triggering to release drugs on-demand, the incorporation of electronic modules, cell encapsulation, biocompatibility and stability. We also review possible applications in drug delivery and cell encapsulation therapy (CET). The results summarized in this review suggest a new strategy to enable construction of "smart", three dimensional drug delivery systems using lithography.
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Affiliation(s)
- Christina L Randall
- Department of Biomedical Engineering, Johns Hopkins University, 720 Rutland Avenue, Baltimore MD 21205, USA
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Bacová Z, Orecná M, Hafko R, Strbák V. Cell swelling-induced signaling for insulin secretion bypasses steps involving G proteins and PLA2 and is N-ethylmaleimide insensitive. Cell Physiol Biochem 2007; 20:387-96. [PMID: 17762166 DOI: 10.1159/000107523] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/19/2007] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND This study was undertaken to examine putative mechanisms of calcium independent signal transduction pathway of cell swelling-induced insulin secretion. METHODS The role of phospholipase A(2), G proteins, and soluble N-ethylmaleimide-sensitive-factor attachment protein receptor (SNARE) in insulin secretion induced by 30% hypotonic medium was studied using isolated rat pancreatic islets. RESULTS In contrast to glucose stimulation, osmotically induced insulin secretion from pancreatic islets was not inhibited by 10 micromol/l bromoenol lactone, an iPLA(2) (Ca(2+) independent phospholipase) inhibitor. Similarly, preincubation of islets for 20 hours with 25 microg/ml mycophenolic acid to inhibit GTP synthesis fully abolished glucose-induced insulin secretion but was without effect on hypotonicity stimulated insulin release. Glucose-induced insulin secretion was prevented by preincubation with 20 nmol/l tetanus toxin (TeTx), a metalloprotease inactivating soluble SNARE. Cell swelling-induced insulin secretion was inhibited by TeTx in the presence of calcium ions but not in calcium depleted medium. The presence of N-ethylmaleimide (NEM, 5 mmol/l, another inhibitor of SNARE proteins) in the medium resulted in high basal insulin secretion and lacking response to glucose stimulation. In contrast, high basal insulin secretion from NEM treated islets further increased after hypotonic stimulation. CONCLUSION G proteins and iPLA(2) - putative mediators of Ca(2+) independent signaling pathway participate in glucose but not in hypotonicity-induced insulin secretion. Hypotonicity-induced insulin secretion is sensitive to clostridial neurotoxin TeTx but is resistant to NEM.
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Affiliation(s)
- Zuzana Bacová
- Institute of Experimental Endocrinology, Slovak Academy of Sciences, Bratislava, Slovakia
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Best L, Elliott AC, Brown PD. Curcumin induces electrical activity in rat pancreatic beta-cells by activating the volume-regulated anion channel. Biochem Pharmacol 2007; 73:1768-75. [PMID: 17382910 DOI: 10.1016/j.bcp.2007.02.006] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2007] [Revised: 02/09/2007] [Accepted: 02/12/2007] [Indexed: 11/21/2022]
Abstract
Curcumin, the principal active component of turmeric, is reported to exert a number of therapeutic actions, including a hypoglycaemic/antidiabetic action. The underlying mechanisms to this action are essentially unknown. We have investigated the hypothesis that a direct stimulatory action on the pancreatic beta-cell could contribute towards the hypoglycaemic activity of this compound. Electrical and ion channel activity were recorded in rat beta-cells using the patch-clamp technique. beta-Cell volume was measured using a video-imaging technique. Insulin release was measured from intact islets by radioimmunoassay. Curcumin (2-10 microM) activated the volume-regulated anion channel in beta-cells. Single channel studies indicated that activation was the result of increased channel open probability. This effect was accompanied by depolarisation of the cell membrane potential, the generation of electrical activity and enhanced insulin release. Curcumin also decreased beta-cell volume, presumably reflecting loss of Cl(-) (and hence water) as a result of anion channel activation. These findings are consistent with the suggestion that Cl(-) fluxes play an important role in regulating beta-cell function. The stimulation of beta-cell function by curcumin could contribute to the hypoglycaemic actions of this compound, and these findings identify a novel potential therapeutic target for the treatment of type 2 diabetes mellitus.
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Affiliation(s)
- Leonard Best
- Department of Medicine, University of Manchester, Oxford Road, Manchester M13 9WL, UK.
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Louchami K, Zhang Y, Beauwens R, Malaisse WJ, Sener A. Is the glucose-induced phosphate flush in pancreatic islets attributable to gating of volume-sensitive anion channels? Endocrine 2007; 31:1-4. [PMID: 17709891 DOI: 10.1007/s12020-007-0006-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/30/1999] [Revised: 11/30/1999] [Accepted: 11/30/1999] [Indexed: 10/23/2022]
Abstract
D-glucose and other nutrient insulin secretagogues have long been known to induce a transient increase in inorganic phosphate release from pancreatic islets, a phenomenon currently referred to as a "phosphate flush". The objective of this study was to explore the possible participation of volume-sensitive anion channels in such a process. Rat pancreatic islets were preincubated for 60 min in the presence of [32P]orthophosphate and then perifused for 90 min to measure 32P fractional outflow rate and insulin secretion. From minutes 46 to 70 inclusive either the concentration of D-glucose was increased from 1.1 to 8.3 mmol L-1 or the extracellular osmolarity was decreased by reducing the NaCl concentration by 50 mmol L-1. The increase in D-glucose concentration induced a typical phosphate flush and biphasic stimulation of insulin release. Extracellular hypoosmolarity caused a monophasic increase in both effluent radioactivity and insulin output. The inhibitor of volume-sensitive anion channels 5-nitro-2-(3-phenylpropylamino)benzoate (0.1 mmol L-1) inhibited both stimulation of insulin release and phosphate flush induced by either the increase in D-glucose concentration or extracellular hypoosmolarity. It is proposed that gating of volume-sensitive anion channels accounts for the occurrence of the phosphate flush and subsequent stimulation of insulin secretion in response to either an increase in D-glucose concentration or a decrease in extracellular osmolarity.
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Affiliation(s)
- Karim Louchami
- Laboratory of Experimental Hormonology, Brussels Free University, 808 Route de Lennik, Brussels, 1070, Belgium
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Davies SL, Brown PD, Best L. Glucose-induced swelling in rat pancreatic alpha-cells. Mol Cell Endocrinol 2007; 264:61-7. [PMID: 17112656 DOI: 10.1016/j.mce.2006.10.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2006] [Revised: 07/31/2006] [Accepted: 10/05/2006] [Indexed: 11/23/2022]
Abstract
Pancreatic beta-cells increase in volume when exposed to elevated concentrations of extracellular glucose. This study has examined the effects of glucose on the volumes of pancreatic alpha-cells, which like beta-cells are regulated by glucose, and intestinal epithelial Caco-2 cells which are unresponsive to glucose. Cell volume changes were monitored by a video-imaging method. Increasing the extracellular glucose concentration caused a concentration-dependent increase in alpha-cell volume over the range 1-20mM. Glucose-induced swelling was not, however, observed in Caco-2 cells. The glucose-induced swelling in both alpha- and beta-cells was abolished by 0.5mM phloretin, an inhibitor of the GLUT proteins, indicating that GLUT mediated glucose transport is a pre-requisite for swelling. Glucose metabolism also appears to be essential, as islet cell swelling was not observed with 16 mM 3-O-methyl glucose. These data suggest that glucose-induced swelling may be a property exclusive to glucose-regulated cells.
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Affiliation(s)
- Sarah L Davies
- Faculty of Life Sciences, University of Manchester, 2nd Floor Core Technology Facility, 46 Grafton Street, Manchester M13 9NT, United Kingdom
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Beauwens R, Best L, Markadieu N, Crutzen R, Louchami K, Brown P, Yates AP, Malaisse WJ, Sener A. Stimulus-secretion coupling of hypotonicity-induced insulin release in BRIN-BD11 cells. Endocrine 2006; 30:353-63. [PMID: 17526948 DOI: 10.1007/s12020-006-0014-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/21/2006] [Revised: 12/15/2006] [Accepted: 12/21/2006] [Indexed: 11/25/2022]
Abstract
The stimulus-secretion coupling for hypotonicity-induced insulin release was investigated in BRIN-BD11 cells. A 50 mM decrease in extracellular NaCl caused a twofold increase in insulin release. The release of insulin evoked by hypotonicity progressively decreased in an exponential manner. The response to extracellular hypotonicity displayed a threshold value close to 20 mOsmol/L and a maximal response at about 70 mOsmol/ L. Hypotonicity also caused a rapid increase in cell volume followed by a regulatory volume decrease (RVD), cell membrane depolarization with induction of spike activity, and a rise in cytosolic Ca2+ concentration. 5-Nitro-2-(3-phenylpropylamino)benzoate inhibited the secretory response to hypoosmolarity, failed to affect the early increase in cell volume but prevented the RVD, and suppressed the hypotonicity-induced plasma membrane depolarization. Insulin release provoked by hypotonicity was inhibited by verapamil, absence of Ca2+, thapsigargin, furosemide, tributyltin, and diazoxide. On the contrary, tolbutamide augmented modestly insulin release recorded in the hypoosmolar medium. Last, a rise in extracellular K+ concentration, while augmenting basal insulin output, failed to affect insulin release in the hypoosmolar medium. Thus, the insulin secretory response to hypotonicity apparently represents a Ca2+-dependent process triggered by the gating of volume-sensitive anion channels with subsequent depolarization and gating of voltage-sensitive Ca2+ channels.
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Affiliation(s)
- Renaud Beauwens
- Laboratorie of Cell and Molecular Physiology, Brussels Free University, Brussels, Belgium
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Takii M, Ishikawa T, Tsuda H, Kanatani K, Sunouchi T, Kaneko Y, Nakayama K. Involvement of stretch-activated cation channels in hypotonically induced insulin secretion in rat pancreatic β-cells. Am J Physiol Cell Physiol 2006; 291:C1405-11. [PMID: 16822943 DOI: 10.1152/ajpcell.00519.2005] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In isolated rat pancreatic β-cells, hypotonic stimulation elicited an increase in cytosolic Ca2+ concentration ([Ca2+]c) at 2.8 mM glucose. The hypotonically induced [Ca2+]c elevation was significantly suppressed by nicardipine, a voltage-dependent Ca2+ channel blocker, and by Gd3+, amiloride, 2-aminoethoxydiphenylborate, and ruthenium red, all cation channel blockers. In contrast, the [Ca2+]c elevation was not inhibited by suramin, a P2 purinoceptor antagonist. Whole cell patch-clamp analyses showed that hypotonic stimulation induced membrane depolarization of β-cells and produced outwardly rectifying cation currents; Gd3+ inhibited both responses. Hypotonic stimulation also increased insulin secretion from isolated rat islets, and Gd3+ significantly suppressed this secretion. Together, these results suggest that osmotic cell swelling activates cation channels in rat pancreatic β-cells, thereby causing membrane depolarization and subsequent activation of voltage-dependent Ca2+ channels and thus elevating insulin secretion.
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Affiliation(s)
- Miki Takii
- Department of Cellular and Molecular Pharmacology, Graduate School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka City, Shizuoka, Japan
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