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Michelucci A, Catacuzzeno L. Piezo1, the new actor in cell volume regulation. Pflugers Arch 2024; 476:1023-1039. [PMID: 38581527 PMCID: PMC11166825 DOI: 10.1007/s00424-024-02951-y] [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: 01/11/2024] [Revised: 02/29/2024] [Accepted: 03/20/2024] [Indexed: 04/08/2024]
Abstract
All animal cells control their volume through a complex set of mechanisms, both to counteract osmotic perturbations of the environment and to enable numerous vital biological processes, such as proliferation, apoptosis, and migration. The ability of cells to adjust their volume depends on the activity of ion channels and transporters which, by moving K+, Na+, and Cl- ions across the plasma membrane, generate the osmotic gradient that drives water in and out of the cell. In 2010, Patapoutian's group identified a small family of evolutionarily conserved, Ca2+-permeable mechanosensitive channels, Piezo1 and Piezo2, as essential components of the mechanically activated current that mediates mechanotransduction in vertebrates. Piezo1 is expressed in several tissues and its opening is promoted by a wide range of mechanical stimuli, including membrane stretch/deformation and osmotic stress. Piezo1-mediated Ca2+ influx is used by the cell to convert mechanical forces into cytosolic Ca2+ signals that control diverse cellular functions such as migration and cell death, both dependent on changes in cell volume and shape. The crucial role of Piezo1 in the regulation of cell volume was first demonstrated in erythrocytes, which need to reduce their volume to pass through narrow capillaries. In HEK293 cells, increased expression of Piezo1 was found to enhance the regulatory volume decrease (RVD), the process whereby the cell re-establishes its original volume after osmotic shock-induced swelling, and it does so through Ca2+-dependent modulation of the volume-regulated anion channels. More recently we reported that Piezo1 controls the RVD in glioblastoma cells via the modulation of Ca2+-activated K+ channels. To date, however, the mechanisms through which this mechanosensitive channel controls cell volume and maintains its homeostasis have been poorly investigated and are still far from being understood. The present review aims to provide a broad overview of the literature discussing the recent advances on this topic.
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Affiliation(s)
- A Michelucci
- Department of Chemistry, Biology and Biotechnology, University of Perugia, 06123, Perugia, Italy.
| | - L Catacuzzeno
- Department of Chemistry, Biology and Biotechnology, University of Perugia, 06123, Perugia, Italy.
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2
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Tranter JD, Kumar A, Nair VK, Sah R. Mechanosensing in Metabolism. Compr Physiol 2023; 14:5269-5290. [PMID: 38158369 DOI: 10.1002/cphy.c230005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2024]
Abstract
Electrical mechanosensing is a process mediated by specialized ion channels, gated directly or indirectly by mechanical forces, which allows cells to detect and subsequently respond to mechanical stimuli. The activation of mechanosensitive (MS) ion channels, intrinsically gated by mechanical forces, or mechanoresponsive (MR) ion channels, indirectly gated by mechanical forces, results in electrical signaling across lipid bilayers, such as the plasma membrane. While the functions of mechanically gated channels within a sensory context (e.g., proprioception and touch) are well described, there is emerging data demonstrating functions beyond touch and proprioception, including mechanoregulation of intracellular signaling and cellular/systemic metabolism. Both MR and MS ion channel signaling have been shown to contribute to the regulation of metabolic dysfunction, including obesity, insulin resistance, impaired insulin secretion, and inflammation. This review summarizes our current understanding of the contributions of several MS/MR ion channels in cell types implicated in metabolic dysfunction, namely, adipocytes, pancreatic β-cells, hepatocytes, and skeletal muscle cells, and discusses MS/MR ion channels as possible therapeutic targets. © 2024 American Physiological Society. Compr Physiol 14:5269-5290, 2024.
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Affiliation(s)
- John D Tranter
- Department of Internal Medicine, Cardiovascular Division, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Ashutosh Kumar
- Department of Internal Medicine, Cardiovascular Division, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Vinayak K Nair
- Department of Internal Medicine, Cardiovascular Division, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Rajan Sah
- Department of Internal Medicine, Cardiovascular Division, Washington University School of Medicine, St. Louis, Missouri, USA
- Center for Cardiovascular Research, Washington University, St. Louis, Missouri, USA
- St. Louis VA Medical Center, St. Louis, Missouri, USA
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3
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Michelucci A, Sforna L, Di Battista A, Franciolini F, Catacuzzeno L. Ca 2+ -activated K + channels regulate cell volume in human glioblastoma cells. J Cell Physiol 2023; 238:2120-2134. [PMID: 37431808 DOI: 10.1002/jcp.31072] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2023] [Revised: 06/10/2023] [Accepted: 06/20/2023] [Indexed: 07/12/2023]
Abstract
Glioblastoma (GBM), the most lethal form of brain tumors, bases its malignancy on the strong ability of its cells to migrate and invade the narrow spaces of healthy brain parenchyma. Cell migration and invasion are both critically dependent on changes in cell volume and shape driven by the transmembrane transport of osmotically important ions such as K+ and Cl- . However, while the Cl- channels participating in cell volume regulation have been clearly identified, the precise nature of the K+ channels involved is still uncertain. Using a combination of electrophysiological and imaging approaches in GBM U87-MG cells, we found that hypotonic-induced cell swelling triggered the opening of Ca2+ -activated K+ (KCa ) channels of large and intermediate conductance (BKCa and IKCa , respectively), both highly expressed in GBM cells. The influx of Ca2+ mediated by the hypotonic-induced activation of mechanosensitive channels was found to be a key step for opening both the BKCa and the IKCa channels. Finally, the activation of both KCa channels mediated by mechanosensitive channels was found to be essential for the development of the regulatory volume decrease following hypotonic shock. Taken together, these data indicate that KCa channels are the main K+ channels responsible for the volume regulation in U87-MG cells.
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Affiliation(s)
- Antonio Michelucci
- Department of Chemistry, Biology, and Biotechnology, University of Perugia, Perugia, Italy
| | - Luigi Sforna
- Department of Chemistry, Biology, and Biotechnology, University of Perugia, Perugia, Italy
| | - Angela Di Battista
- Department of Chemistry, Biology, and Biotechnology, University of Perugia, Perugia, Italy
| | - Fabio Franciolini
- Department of Chemistry, Biology, and Biotechnology, University of Perugia, Perugia, Italy
| | - Luigi Catacuzzeno
- Department of Chemistry, Biology, and Biotechnology, University of Perugia, Perugia, Italy
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4
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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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Sforna L, Michelucci A, Morena F, Argentati C, Franciolini F, Vassalli M, Martino S, Catacuzzeno L. Piezo1 controls cell volume and migration by modulating swelling-activated chloride current through Ca 2+ influx. J Cell Physiol 2021; 237:1857-1870. [PMID: 34913176 DOI: 10.1002/jcp.30656] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Revised: 11/23/2021] [Accepted: 11/25/2021] [Indexed: 12/21/2022]
Abstract
Regulatory volume decrease (RVD), a homeostatic process responsible for the re-establishment of the original cell volume upon swelling, is critical in controlling several functions, including migration. RVD is mainly sustained by the swelling-activated Cl- current (ICl,swell ), which can be modulated by cytoplasmic Ca2+ . Cell swelling also activates mechanosensitive channels, including the ubiquitously expressed Ca2+ -permeable channel Piezo1. We hypothesized that, by controlling cytoplasmic Ca2+ and in turn ICl,swell , Piezo1 is involved in the fine regulation of RVD and cell migration. We compared RVD and ICl,swell in wild-type (WT) HEK293T cells, which express endogenous levels of Piezo1, and in cells overexpressing (OVER) or knockout (KO) for Piezo1. Compared to WT, RVD was markedly increased in OVER, while virtually absent in KO cells. Consistently, ICl,swell amplitude was highest in OVER and lowest in KO cells, with WT cells displaying an intermediate level, suggesting a Ca2+ -dependent modulation of the current by Piezo1 channels. Indeed, in the absence of external Ca2+ , ICl,swell in both WT and OVER cells, as well as the RVD probed in OVER cells, were significantly lower than in the presence of Ca2+ and no longer different compared to KO cells. However, the Piezo-mediated Ca2+ influx was ineffective in enhancing ICl,swell in the absence of releasable Ca2+ from intracellular stores. The different expression levels of Piezo1 affected also cell migration which was strongly enhanced in OVER, while reduced in KO cells, as compared to WT. Taken together, our data indicate that Piezo1 controls RVD and migration in HEK293T cells by modulating ICl,swell through Ca2+ influx.
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Affiliation(s)
- Luigi Sforna
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
| | - Antonio Michelucci
- Department of Neuroscience, Imaging and Clinical Sciences, University G. d'Annunzio of Chieti, Chieti, Italy
| | - Francesco Morena
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
| | - Chiara Argentati
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
| | - Fabio Franciolini
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
| | - Massimo Vassalli
- James Watt School of Engineering, University of Glasgow, Center for the Cellular Microenvironment, School of Engineering, G12 8LT, Glasgow, UK
| | - Sabata Martino
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy.,CEMIN, Center of Excellence on Nanostructured Innovative Materials, University of Perugia, Perugia, Italy
| | - Luigi Catacuzzeno
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
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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: 26] [Impact Index Per Article: 5.2] [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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7
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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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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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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: 59] [Impact Index Per Article: 9.8] [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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Babai N, Kanevsky N, Dascal N, Rozanski GJ, Singh DP, Fatma N, Thoreson WB. Anion-sensitive regions of L-type CaV1.2 calcium channels expressed in HEK293 cells. PLoS One 2010; 5:e8602. [PMID: 20066046 PMCID: PMC2798859 DOI: 10.1371/journal.pone.0008602] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2009] [Accepted: 12/09/2009] [Indexed: 11/21/2022] Open
Abstract
L-type calcium currents (ICa) are influenced by changes in extracellular chloride, but sites of anion effects have not been identified. Our experiments showed that CaV1.2 currents expressed in HEK293 cells are strongly inhibited by replacing extracellular chloride with gluconate or perchlorate. Variance-mean analysis of ICa and cell-attached patch single channel recordings indicate that gluconate-induced inhibition is due to intracellular anion effects on Ca2+ channel open probability, not conductance. Inhibition of CaV1.2 currents produced by replacing chloride with gluconate was reduced from ∼75%–80% to ∼50% by omitting β subunits but unaffected by omitting α2δ subunits. Similarly, gluconate inhibition was reduced to ∼50% by deleting an α1 subunit N-terminal region of 15 residues critical for β subunit interactions regulating open probability. Omitting β subunits with this mutant α1 subunit did not further diminish inhibition. Gluconate inhibition was unchanged with expression of different β subunits. Truncating the C terminus at AA1665 reduced gluconate inhibition from ∼75%–80% to ∼50% whereas truncating it at AA1700 had no effect. Neutralizing arginines at AA1696 and 1697 by replacement with glutamines reduced gluconate inhibition to ∼60% indicating these residues are particularly important for anion effects. Expressing CaV1.2 channels that lacked both N and C termini reduced gluconate inhibition to ∼25% consistent with additive interactions between the two tail regions. Our results suggest that modest changes in intracellular anion concentration can produce significant effects on CaV1.2 currents mediated by changes in channel open probability involving β subunit interactions with the N terminus and a short C terminal region.
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Affiliation(s)
- Norbert Babai
- Department of Ophthalmology & Visual Science, University of Nebraska Medical Center, Omaha, Nebraska, United States of America
| | - Nataly Kanevsky
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Ramat Aviv, Israel
| | - Nathan Dascal
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Ramat Aviv, Israel
| | - George J. Rozanski
- Department of Cellular & Integrative Physiology, University of Nebraska Medical Center, Omaha, Nebraska, United States of America
| | - Dhirendra P. Singh
- Department of Ophthalmology & Visual Science, University of Nebraska Medical Center, Omaha, Nebraska, United States of America
| | - Nigar Fatma
- Department of Ophthalmology & Visual Science, University of Nebraska Medical Center, Omaha, Nebraska, United States of America
| | - Wallace B. Thoreson
- Department of Ophthalmology & Visual Science, University of Nebraska Medical Center, Omaha, Nebraska, United States of America
- * E-mail:
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11
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Hoffmann EK, Lambert IH, Pedersen SF. Physiology of cell volume regulation in vertebrates. Physiol Rev 2009; 89:193-277. [PMID: 19126758 DOI: 10.1152/physrev.00037.2007] [Citation(s) in RCA: 1004] [Impact Index Per Article: 66.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The ability to control cell volume is pivotal for cell function. Cell volume perturbation elicits a wide array of signaling events, leading to protective (e.g., cytoskeletal rearrangement) and adaptive (e.g., altered expression of osmolyte transporters and heat shock proteins) measures and, in most cases, activation of volume regulatory osmolyte transport. After acute swelling, cell volume is regulated by the process of regulatory volume decrease (RVD), which involves the activation of KCl cotransport and of channels mediating K(+), Cl(-), and taurine efflux. Conversely, after acute shrinkage, cell volume is regulated by the process of regulatory volume increase (RVI), which is mediated primarily by Na(+)/H(+) exchange, Na(+)-K(+)-2Cl(-) cotransport, and Na(+) channels. Here, we review in detail the current knowledge regarding the molecular identity of these transport pathways and their regulation by, e.g., membrane deformation, ionic strength, Ca(2+), protein kinases and phosphatases, cytoskeletal elements, GTP binding proteins, lipid mediators, and reactive oxygen species, upon changes in cell volume. We also discuss the nature of the upstream elements in volume sensing in vertebrate organisms. Importantly, cell volume impacts on a wide array of physiological processes, including transepithelial transport; cell migration, proliferation, and death; and changes in cell volume function as specific signals regulating these processes. A discussion of this issue concludes the review.
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Affiliation(s)
- Else K Hoffmann
- Department of Biology, University of Copenhagen, Copenhagen, Denmark.
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12
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Kaneko T, Takahashi N, Kikuyama M. Membrane stretching triggers mechanosensitive Ca2+ channel activation in Chara. J Membr Biol 2009; 228:33-42. [PMID: 19234734 DOI: 10.1007/s00232-009-9156-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2008] [Accepted: 01/22/2009] [Indexed: 11/25/2022]
Abstract
In order to confirm that mechanosensitive Ca(2+) channels are activated by membrane stretching, we stretched or compressed the plasma membrane of Chara by applying osmotic shrinkage or swelling of the cell by varying the osmotic potential of the bathing medium. Aequorin studies revealed that treatments causing membrane stretching induced a transient but large increase in cytoplasmic concentration of Ca(2+) (Delta[Ca(2+)](c)). However, the observed Delta[Ca(2+)](c) decreased during the treatments, resulting in membrane compression. A second experiment was carried out to study the relationship between changes in membrane potential (DeltaE(m)) and stretching or compression of the plasma membrane. Significant DeltaE(m) values, often accompanied by an action potential, were observed during the initial exchange of the bathing medium from a hypotonic medium to a hypertonic one (plasmolysis). DeltaE(m) appears to be triggered by a partial stretching of the membrane as it was peeled from the cell wall. After plasmolysis, other exchanges from hypertonic to hypotonic media, with their accompanying membrane stretching, always induced large DeltaE(m) values and were often accompanied by an action potential. By contrast, action potentials were scarcely observed during other exchanges from hypotonic to hypertonic solutions (=membrane compression). Thus, we concluded that activation of the mechanosensitive channels is triggered by membrane stretching in Chara.
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Affiliation(s)
- Toshiyuki Kaneko
- Graduate School of Science and Technology, Niigata University, Ikarashi, Nishi-ku, Niigata, Japan
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13
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Chen AK, Latz MI, Sobolewski P, Frangos JA. Evidence for the role of G-proteins in flow stimulation of dinoflagellate bioluminescence. Am J Physiol Regul Integr Comp Physiol 2007; 292:R2020-7. [PMID: 17322118 DOI: 10.1152/ajpregu.00649.2006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Luminescent dinoflagellates respond to flow by the production of light. The primary mechanotransduction event is unknown, although downstream events include a calcium flux in the cytoplasm, a self-propagating action potential across the vacuole membrane, and a proton flux into the cytoplasm that activates the luminescent chemistry. Given the role of GTP-binding (G) proteins in the mechanotransduction of flow by nonmarine cells and the presence of G-proteins in dinoflagellates, it was hypothesized that flow-stimulated dinoflagellate bioluminescence involves mechanotransduction by G-proteins. In the present study, osmotic swelling of cells of the dinoflagellate Lingulodinium polyedrum was used as a drug delivery system to introduce GDPbetaS, an inhibitor of G-protein activation. Osmotically swollen cells produced higher levels of flow-stimulated bioluminescence at a lower threshold of shear stress, indicating they were more flow sensitive. GDPbetaS inhibited flow-stimulated bioluminescence in osmotically swollen cells and in cells that were restored to the isosmotic condition following hypoosmotic treatment with GDPbetaS. These results provide evidence that G-proteins are involved in the mechanotransduction of flow in dinoflagellates and suggest that G-protein involvement in mechanotransduction may be a fundamental evolutionary adaptation.
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Affiliation(s)
- Antony K Chen
- La Jolla Bioengineering Institute, La Jolla, CA 92037, USA
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14
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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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15
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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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16
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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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Hafting T, Haug TM, Ellefsen S, Sand O. Hypotonic stress activates BK channels in clonal kidney cells via purinergic receptors, presumably of the P2Y subtype. Acta Physiol (Oxf) 2006; 188:21-31. [PMID: 16911250 DOI: 10.1111/j.1748-1716.2006.01601.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
AIM Membrane stretch due to cell swelling may cause a minute leakage of adenosine triphosphate (ATP) that stimulates endogenous purinergic receptors. The following elevation of the cytosolic-free Ca(2+) concentration ([Ca(2+)](i)) may then participate in cell volume regulation. The aim of the present study was to test if purinergic receptors and large conductance Ca(2+) activated K(+) (BK) channels are activated in response to hypotonic stress in clonal kidney cells (Vero cells). METHODS The methods used are fura-2 microfluorometry, cell-attached patch clamp and reverse-transcriptase polymerase chain reaction (RT-PCR). METHODS Subjecting cells to hypotonic stress for 10 s by exposure to a solution with 45% reduced osmolality induced a transient rise in [Ca(2+)](i). This response persisted in virtually Ca(2+)-free extracellular solution, demonstrating that Ca(2+) was mainly released from intracellular stores. The hypotonically induced elevation of [Ca(2+)](i) was completely inhibited by the P2 receptor antagonists suramine (100 microM) and pyridoxalphosphate-6-azophenyl-2'4'-disulphonate (PPADS; 20 microM), indicating that extracellular ATP is crucial for the [Ca(2+)](i) increase. RT-PCR revealed the expression of mRNA for P2Y(1) receptors in Vero cells. The putatively selective P2Y(1) antagonist PPADS did completely block Ca(2+) responses to both ATP and hypotonic stress, suggesting that P2Y(1) receptors are mediating the response. Furthermore, patch clamp recordings in cell-attached configuration revealed that BK channels are activated in response to hypotonic stress. conclusion: Vero cells express functional purinergic receptors, presumably of the P2Y(1) subtype. These receptors are responsible for the elevation of [Ca(2+)](i) evoked by hypotonic stress. The concurrent activation of BK channels permits K(+) efflux that may contribute to regulatory volume decrease.
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Affiliation(s)
- T Hafting
- Department of Molecular Biosciences, University of Oslo, Oslo, Norway
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Kaneko T, Saito C, Shimmen T, Kikuyama M. Possible involvement of mechanosensitive Ca2+ channels of plasma membrane in mechanoperception in Chara. PLANT & CELL PHYSIOLOGY 2005; 46:130-135. [PMID: 15659450 DOI: 10.1093/pcp/pci004] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
When an internodal cell of Chara corallina was stimulated with a mechanical pulse of various amplitudes lasting for 0.1 s (mechanical stimulus), the cell generated a receptor potential, which was highly dependent not only on the strength of the stimulus but also on the extracellular Cl- concentration. Extracellular Ca2+ was indispensable for generating receptor potential, since removal of Ca2+ reversibly inhibited generation of the receptor potential. The cytoplasmic Ca2+ level transiently rose upon mechanical stimulation. The stronger the mechanical stimulus, the larger was the increase in the cytoplasmic level of Ca2+. It is proposed that the first step of receptor potential is an activation of mechanosensitive Ca2+ channels at the plasma membrane.
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Affiliation(s)
- Toshiyuki Kaneko
- Graduate School of Science and Technology, Niigata University, Niigata, 950-2181 Japan
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Kwon SH, Guggino WB. Multiple sequences in the C terminus of MaxiK channels are involved in expression, movement to the cell surface, and apical localization. Proc Natl Acad Sci U S A 2004; 101:15237-42. [PMID: 15469924 PMCID: PMC524057 DOI: 10.1073/pnas.0404877101] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Apical expression of the large-conductance, calcium- and voltage-activated potassium (MaxiK) channel in the cortical collecting duct is responsible for flow-stimulated potassium secretion. Here, we identify two cytoplasmic regions controlling apical expression of the MaxiK channel. Disruption of the proximal region results in the intracellular retention of the MaxiK channel without affecting channel assembly, thereby reducing surface expression. Coexpression of the WT channel with this mutant results in a reduction of WT MaxiK channel at the cell surface. Our data indicate that this proximal region is necessary for export of the MaxiK channel from the endoplasmic reticulum as a way to assess the final assembly of the channel. Deletion of a more distal region disrupts apical sorting, resulting in a nonpolarized distribution of the channel without impairing its surface delivery. In summary, we have found that sequences of amino acids in the C terminus of the MaxiK channel operate after the channel is assembled into a multimer and play a role in its expression, movement to the cell surface, and apical localization.
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Affiliation(s)
- Sang-Ho Kwon
- Department of Physiology, School of Medicine, The Johns Hopkins University, Baltimore, MD 21205, USA
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20
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Falktoft B, Lambert IH. Ca2+-mediated Potentiation of the Swelling-induced Taurine Efflux from HeLa Cells: On the Role of Calmodulin and Novel Protein Kinase C Isoforms. J Membr Biol 2004; 201:59-75. [PMID: 15630544 DOI: 10.1007/s00232-004-0705-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2004] [Revised: 07/19/2004] [Indexed: 11/27/2022]
Abstract
The present work sets out to investigate how Ca(2+) regulates the volume-sensitive taurine-release pathway in HeLa cells. Addition of Ca(2+)-mobilizing agonists at the time of exposure to hypotonic NaCl medium augments the swelling-induced taurine release and subsequently accelerates the inactivation of the release pathway. The accelerated inactivation is not observed in hypotonic Ca(2+)-free or high-K(+) media. Addition of Ca(2+)-mobilizing agonists also accelerates the regulatory volume decrease, which probably reflects activation of Ca(2+)-activated K(+) channels. The taurine release from control cells and cells exposed to Ca(2+) agonists is equally affected by changes in cell volume, application of DIDS and arachidonic acid, indicating that the volume-sensitive taurine leak pathway mediates the Ca(2+)-augmented taurine release. Exposure to Ca(2+)-mobilizing agonists prior to a hypotonic challenge also augments a subsequent swelling-induced taurine release even though the intracellular Ca(2+)-concentration has returned to the unstimulated level. The Ca(2+)-induced augmentation of the swelling-induced taurine release is abolished by inhibition of calmodulin, but unaffected by inhibition of calmodulin-dependent kinase II, myosin light chain kinase and calcineurin. The effect of Ca(2+)-mobilizing agonists is mimicked by protein kinase C (PKC) activation and abolished in the presence of the PKC inhibitor Gö6850 and following downregulation of phorbol ester-sensitive PKC isoforms. It is suggested that Ca(2+) regulates the volume-sensitive taurine-release pathway through activation of calmodulin and PKC isoforms belonging to the novel subclass (nPKC).
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Affiliation(s)
- B Falktoft
- Biochemical Department, August Krogh Institute, Universitetsparken 13, Copenhagen, DK-2100 Denmark
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Basavappa S, Mangel AW, Boulpaep EL. Calcium-dependent, swelling-activated K+ conductance in human neuroblastoma cells. Biochem Biophys Res Commun 2003; 308:759-63. [PMID: 12927783 DOI: 10.1016/s0006-291x(03)01481-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In most mammalian cells, regulatory volume decrease (RVD) is mediated by swelling-activated Cl(-) and K(+) channels. Previous studies in the human neuroblastoma cell line CHP-100 have demonstrated that exposure to hypoosmotic solutions activates Cl(-) channels which are sensitive to Ca(2+). Whether a Ca(2+)-dependent K(+) conductance is activated after cell swelling was investigated in the present studies. Reducing the extracellular osmolarity from 290 to 190 mOsm/kg H(2)O rapidly activated 86Rb effluxes. Hypoosmotic stress also increased cytosolic Ca(2+) in fura-2 loaded cells. Pretreatment with 2.5 mM EGTA and nominally Ca(2+) free extracellular solution significantly decreased the hypoosmotically induced rise in cytosolic Ca(2+) and the swelling-activated 86Rb efflux. In cell-attached patch-clamp studies, decreasing the extracellular osmolarity activated a K(+) conductance that was blocked by Ba(2+). In addition, the swelling-activated K(+) channels were significantly inhibited in the presence of nominally free extracellular Ca(2+) and 2.5mM EGTA. These results suggest that in response to hypoosmotic stress, a Ca(2+)-dependent K(+) conductance is activated in the human neuroblastoma cell line CHP-100.
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Affiliation(s)
- Srisaila Basavappa
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520, USA.
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