1
|
Dissanayake WC, Shepherd PR. β-cells retain a pool of insulin-containing secretory vesicles regulated by adherens junctions and the cadherin binding protein p120 catenin. J Biol Chem 2022; 298:102240. [PMID: 35809641 PMCID: PMC9358467 DOI: 10.1016/j.jbc.2022.102240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Revised: 06/16/2022] [Accepted: 06/17/2022] [Indexed: 11/03/2022] Open
Abstract
The β-cells of the islets of Langerhans are the sole producers of insulin in the human body. In response to rising glucose levels, insulin-containing vesicles inside β-cells fuse with the plasma membrane and release their cargo. However, the mechanisms regulating this process are only partly understood. Previous evidence indicated reductions in α-catenin elevate insulin release, while reductions in β-catenin decrease insulin release. α- and β-catenin contribute to cellular regulation in a range of ways but one is as members of the adherens junction complex and these contribute to the development of cell polarity in b-cells. Therefore, we investigated the effects of adherens junctions on insulin release. We show in INS-1E β-cells knockdown of either E- or N-cadherin had only small effects on insulin secretion, but simultaneous knockout of both cadherins resulted in a significant increase in basal insulin release to the same level as glucose-stimulated release. This double knockdown also significantly attenuated levels of p120 catenin, a cadherin binding partner involved in regulating cadherin turnover. Conversely, reducing p120 catenin levels with siRNA destabilized both E- and N-cadherin, and this was also associated with an increase in levels of insulin secreted from INS-1E cells. Furthermore, there were also changes in these cells consistent with higher insulin release, namely reductions in levels of F-actin and increased intracellular free Ca2+ levels in response to KCl-induced membrane depolarization. Taken together, these data provide evidence that adherens junctions play important roles in retaining a pool of insulin secretory vesicles within the cell and establish a role for p120 catenin in regulating this process.
Collapse
Affiliation(s)
- Waruni C Dissanayake
- Department of Molecular Medicine and Pathology, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
| | - Peter R Shepherd
- Department of Molecular Medicine and Pathology, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
| |
Collapse
|
2
|
Abstract
Beta cells of the pancreatic islet express many different types of ion channels. These channels reside in the β-cell plasma membrane as well as subcellular organelles and their coordinated activity and sensitivity to metabolism regulate glucose-dependent insulin secretion. Here, we review the molecular nature, expression patterns, and functional roles of many β-cell channels, with an eye toward explaining the ionic basis of glucose-induced insulin secretion. Our primary focus is on KATP and voltage-gated Ca2+ channels as these primarily regulate insulin secretion; other channels in our view primarily help to sculpt the electrical patterns generated by activated β-cells or indirectly regulate metabolism. Lastly, we discuss why understanding the physiological roles played by ion channels is important for understanding the secretory defects that occur in type 2 diabetes. © 2021 American Physiological Society. Compr Physiol 11:1-21, 2021.
Collapse
Affiliation(s)
- Benjamin Thompson
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, USA
- Brehm Diabetes Research Center, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | | |
Collapse
|
3
|
ATP-sensitive K + channels and mitochondrial permeability transition pore mediate effects of hydrogen sulfide on cytosolic Ca 2+ homeostasis and insulin secretion in β-cells. Pflugers Arch 2019; 471:1551-1564. [PMID: 31713764 DOI: 10.1007/s00424-019-02325-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2019] [Revised: 09/29/2019] [Accepted: 10/21/2019] [Indexed: 12/19/2022]
Abstract
Hydrogen sulfide (H2S) is endogenously produced in pancreatic ß cells and its level is elevated in diabetes. Here, we report that H2S affects insulin secretion via two mechanisms that converge on cytosolic free Ca2+ ([Ca2+]i), a key mediator of insulin exocytosis. Cellular calcium imaging, using Fura-2 or Fluo-4, showed that exposure of INS-1E cells to H2S (30-100 μM) reduced both [Ca2+]i levels (by 21.7 ± 2.3%) and oscillation frequency (p < 0.01, n = 4). Consistent with a role of plasma membrane KATP channels (plasma-KATP), the effects of H2S on [Ca2+]i were blocked by gliclazide (a blocker of plasma-KATP channels), but were mimicked by diazoxide (an activator of plasma-KATP channels). Surprisingly, when Ca2+ entry via plasma membrane was inhibited using Ca2+-free external solutions, H2S increased [Ca2+]i by 39.7 ± 3.6% suggesting Ca2+ release from intracellular stores. H2S-induced [Ca2+]i increases were abolished by either FCCP (which depletes Ca2+ stored in mitochondria) or cyclosporine A (an inhibitor of mitochondrial permeability transition pore, mPTP) suggesting that H2S induces Ca2+ release from mitochondria. Measurement of mitochondrial membrane potential (MMP) suggested that H2S causes MMP depolarization, which was blocked by cyclosporine A. Finally, insulin measurements by ELISA indicated that H2S decreased insulin release from INS-1E cells, but after plasma membrane Ca2+ entry was blocked by nifedipine, H2S-induced mitochondrial Ca2+ release is able to increase insulin release. Together, our results indicate that H2S has dual effects on insulin release suggesting that, with different metabolic conditions, H2S may differentially modulate the insulin release from pancreatic ß cells and play a role in ß cell dysfunction.
Collapse
|
4
|
Esteghamat F, Broughton JS, Smith E, Cardone R, Tyagi T, Guerra M, Szabó A, Ugwu N, Mani MV, Azari B, Kayingo G, Chung S, Fathzadeh M, Weiss E, Bender J, Mane S, Lifton RP, Adeniran A, Nathanson MH, Gorelick FS, Hwa J, Sahin-Tóth M, Belfort-DeAguiar R, Kibbey RG, Mani A. CELA2A mutations predispose to early-onset atherosclerosis and metabolic syndrome and affect plasma insulin and platelet activation. Nat Genet 2019; 51:1233-1243. [PMID: 31358993 PMCID: PMC6675645 DOI: 10.1038/s41588-019-0470-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Accepted: 06/20/2019] [Indexed: 12/12/2022]
Abstract
Factors that underlie the clustering of metabolic syndrome traits are not fully known. We performed whole-exome sequence analysis in kindreds with extreme phenotypes of early-onset atherosclerosis and metabolic syndrome, and identified novel loss-of-function mutations in the gene encoding the pancreatic elastase chymotrypsin-like elastase family member 2A (CELA2A). We further show that CELA2A is a circulating enzyme that reduces platelet hyperactivation, triggers both insulin secretion and degradation, and increases insulin sensitivity. CELA2A plasma levels rise postprandially and parallel insulin levels in humans. Loss of these functions by the mutant proteins provides insight into disease mechanisms and suggests that CELA2A could be an attractive therapeutic target.
Collapse
Affiliation(s)
| | - James S Broughton
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Emily Smith
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Rebecca Cardone
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Tarun Tyagi
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Mateus Guerra
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - András Szabó
- Center for Exocrine Disorders, Department of Molecular and Cell Biology, Boston University Henry M. Goldman School of Dental Medicine, Boston, MA, USA
| | - Nelson Ugwu
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Mitra V Mani
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Bani Azari
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Gerald Kayingo
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Sunny Chung
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Mohsen Fathzadeh
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Ephraim Weiss
- Department of Medicine, NYU Medical Center, New York, NY, USA
| | - Jeffrey Bender
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Shrikant Mane
- Department of Genetics, Yale School of Medicine, New Haven, CT, USA
| | - Richard P Lifton
- Laboratory of Human Genetics and Genomics, The Rockefeller University, New York, NY, USA
| | | | - Michael H Nathanson
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Fred S Gorelick
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - John Hwa
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Miklós Sahin-Tóth
- Center for Exocrine Disorders, Department of Molecular and Cell Biology, Boston University Henry M. Goldman School of Dental Medicine, Boston, MA, USA
| | | | - Richard G Kibbey
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Arya Mani
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA.
- Department of Genetics, Yale School of Medicine, New Haven, CT, USA.
| |
Collapse
|
5
|
Postnatal Increases in Axonal Conduction Velocity of an Identified Drosophila Interneuron Require Fast Sodium, L-Type Calcium and Shaker Potassium Channels. eNeuro 2019; 6:ENEURO.0181-19.2019. [PMID: 31253715 PMCID: PMC6709211 DOI: 10.1523/eneuro.0181-19.2019] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2019] [Revised: 06/06/2019] [Accepted: 06/12/2019] [Indexed: 11/21/2022] Open
Abstract
During early postnatal life, speed up of signal propagation through many central and peripheral neurons has been associated with an increase in axon diameter or/and myelination. Especially in unmyelinated axons postnatal adjustments of axonal membrane conductances is potentially a third mechanism but solid evidence is lacking. Here, we show that axonal action potential (AP) conduction velocity in the Drosophila giant fiber (GF) interneuron, which is required for fast long-distance signal conduction through the escape circuit, is increased by 80% during the first day of adult life. Genetic manipulations indicate that this postnatal increase in AP conduction velocity in the unmyelinated GF axon is likely owed to adjustments of ion channel expression or properties rather than axon diameter increases. Specifically, targeted RNAi knock-down of either Para fast voltage-gated sodium, Shaker potassium (Kv1 homologue), or surprisingly, L-type like calcium channels counteracts postnatal increases in GF axonal conduction velocity. By contrast, the calcium-dependent potassium channel Slowpoke (BK) is not essential for postnatal speeding, although it also significantly increases conduction velocity. Therefore, we identified multiple ion channels that function to support fast axonal AP conduction velocity, but only a subset of these are regulated during early postnatal life to maximize conduction velocity. Despite its large diameter (∼7 µm) and postnatal regulation of multiple ionic conductances, mature GF axonal conduction velocity is still 20-60 times slower than that of vertebrate Aβ sensory axons and α motoneurons, thus unraveling the limits of long-range information transfer speed through invertebrate circuits.
Collapse
|
6
|
Ujike A, Otsuguro KI, Miyamoto R, Yamaguchi S, Ito S. Bidirectional effects of hydrogen sulfide via ATP-sensitive K+ channels and transient receptor potential A1 channels in RIN14B cells. Eur J Pharmacol 2015; 764:463-470. [DOI: 10.1016/j.ejphar.2015.07.029] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2015] [Revised: 07/09/2015] [Accepted: 07/10/2015] [Indexed: 12/22/2022]
|
7
|
Wang Y, Jarrard RE, Pratt EPS, Guerra ML, Salyer AE, Lange AM, Soderling IM, Hockerman GH. Uncoupling of Cav1.2 from Ca(2+)-induced Ca(2+) release and SK channel regulation in pancreatic β-cells. Mol Endocrinol 2014; 28:458-76. [PMID: 24506535 DOI: 10.1210/me.2013-1094] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
We investigated the role of Cav1.2 in pancreatic β-cell function by expressing a Cav1.2 II-III loop/green fluorescent protein fusion in INS-1 cells (Cav1.2/II-III cells) to disrupt channel-protein interactions. Neither block of KATP channels nor stimulation of membrane depolarization by tolbutamide was different in INS-1 cells compared with Cav1.2/II-III cells, but whole-cell Cav current density was significantly increased in Cav1.2/II-III cells. Tolbutamide (200 μM) stimulated insulin secretion and Ca(2+) transients in INS-1 cells, and Cav1.2/II-III cells were completely blocked by nicardipine (2 μM), but thapsigargin (1 μM) blocked tolbutamide-stimulated secretion and Ca(2+) transients only in INS-1 cells. Tolbutamide-stimulated endoplasmic reticulum [Ca(2+)] decrease was reduced in Cav1.2/II-III cells compared with INS-1 cells. However, Ca(2+) transients in both INS-1 cells and Cav1.2/II-III cells were significantly potentiated by 8-pCPT-2'-O-Me-cAMP (5 μM), FPL-64176 (0.5 μM), or replacement of extracellular Ca(2+) with Sr(2+). Glucose (10 mM) + glucagon-like peptide-1 (10 nM) stimulated discrete spikes in [Ca(2+)]i in the presence of verapamil at a higher frequency in INS-1 cells than in Cav1.2/II-II cells. Glucose (18 mM) stimulated more frequent action potentials in Cav1.2/II-III cells and primary rat β-cells expressing the Cav1.2/II-II loop than in control cells. Further, apamin (1 μM) increased glucose-stimulated action potential frequency in INS-1 cells, but not Cav1.2/II-III cells, suggesting that SK channels were not activated under these conditions in Cav1.2/II-III loop-expressing cells. We propose the II-III loop of Cav1.2 as a key molecular determinant that couples the channel to Ca(2+)-induced Ca(2+) release and activation of SK channels in pancreatic β-cells.
Collapse
Affiliation(s)
- Yuchen Wang
- Purdue University Life Sciences Graduate Program (R.E.J., E.P.S.P., A.M.L.) and Department of Medicinal Chemistry and Molecular Pharmacology (Y.W., M.L.G., A.E.S., I.M.S., G.H.H.), Purdue University, West Lafayette, Indiana 47907-2091
| | | | | | | | | | | | | | | |
Collapse
|
8
|
Huang H, Tan BZ, Shen Y, Tao J, Jiang F, Sung YY, Ng CK, Raida M, Köhr G, Higuchi M, Fatemi-Shariatpanahi H, Harden B, Yue DT, Soong TW. RNA editing of the IQ domain in Ca(v)1.3 channels modulates their Ca²⁺-dependent inactivation. Neuron 2012; 73:304-16. [PMID: 22284185 DOI: 10.1016/j.neuron.2011.11.022] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/29/2011] [Indexed: 11/29/2022]
Abstract
Adenosine-to-inosine RNA editing is crucial for generating molecular diversity, and serves to regulate protein function through recoding of genomic information. Here, we discover editing within Ca(v)1.3 Ca²⁺ channels, renown for low-voltage Ca²⁺-influx and neuronal pacemaking. Significantly, editing occurs within the channel's IQ domain, a calmodulin-binding site mediating inhibitory Ca²⁺-feedback (CDI) on channels. The editing turns out to require RNA adenosine deaminase ADAR2, whose variable activity could underlie a spatially diverse pattern of Ca(v)1.3 editing seen across the brain. Edited Ca(v)1.3 protein is detected both in brain tissue and within the surface membrane of primary neurons. Functionally, edited Ca(v)1.3 channels exhibit strong reduction of CDI; in particular, neurons within the suprachiasmatic nucleus show diminished CDI, with higher frequencies of repetitive action-potential and calcium-spike activity, in wild-type versus ADAR2 knockout mice. Our study reveals a mechanism for fine-tuning Ca(v)1.3 channel properties in CNS, which likely impacts a broad spectrum of neurobiological functions.
Collapse
Affiliation(s)
- Hua Huang
- Department of Physiology, Yong Loo Lin School Medicine, National University of Singapore, 117597 Singapore
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
9
|
Jacobo SMP, Guerra ML, Hockerman GH. Cav1.2 and Cav1.3 are differentially coupled to glucagon-like peptide-1 potentiation of glucose-stimulated insulin secretion in the pancreatic beta-cell line INS-1. J Pharmacol Exp Ther 2009; 331:724-32. [PMID: 19710366 PMCID: PMC2775263 DOI: 10.1124/jpet.109.158519] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2009] [Accepted: 08/25/2009] [Indexed: 02/06/2023] Open
Abstract
The incretin peptides, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), potentiate glucose-stimulated insulin secretion (GSIS) and beta-cell proliferation and differentiation. Ca(2+) influx via voltage-gated L-type Ca(2+) channels is required for GLP-1 and GIP potentiation of GSIS. We investigated the role of the L-type Ca(2+) channels Ca(v)1.2 and Ca(v)1.3 in mediating GLP-1- and GIP-stimulated events in INS-1 cells and INS-1 cell lines expressing dihydropyridine-insensitive (DHPi) mutants of either Ca(v)1.2 or Ca(v)1.3. Ca(v)1.3/DHPi channels supported full potentiation of GSIS by GLP-1 (50 nM) compared with untransfected INS-1 cells. However, GLP-1-potentiated GSIS mediated by Ca(v)1.2/DHPi channels was markedly reduced compared with untransfected INS-1 cells. In contrast, GIP (10 nM) potentiation of GSIS mediated by both Ca(v)1.2/DHPi and Ca(v)1.3/DHPi channels was similar to that observed in untransfected INS-1 cells. Disruption of intracellular Ca(2+) release with thapsigargin, ryanodine, or 2-aminoethyldiphenylborate and inhibition of protein kinase A (PKA) or protein kinase C (PKC) significantly reduced GLP-1 potentiation of GSIS by Ca(v)1.3/DHPi channels and by endogenous L-type channels in INS-1 cells, but not by Ca(v)1.2/DHPi channels. Inhibition of glucose-stimulated phospholipase C activity with 1-(6-((17b-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U73122) did not inhibit potentiation of GSIS by GLP-1 in INS-1 cells. In contrast, wortmannin, an inhibitor of phosphatidylinositol 3-kinase, and 2'-amino-3'-methoxyflavone (PD98059), an inhibitor of mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase, both markedly inhibited GLP-1 potentiation of GSIS by endogenous channels in INS-1 cells and Ca(v)1.3/DHPi channels, but not by Ca(v)1.2/DHPi channels. Thus, Ca(v)1.3 is preferentially coupled to GLP-1 potentiation of GSIS in INS-1 cells via a mechanism that requires intact intracellular Ca(2+) stores, PKA and PKC activity, and activation of ERK1/2.
Collapse
Affiliation(s)
- Sarah Melissa P Jacobo
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana, USA
| | | | | |
Collapse
|
10
|
Fu Y, Tian W, Pratt EB, Dirling LB, Shyng SL, Meshul CK, Cohen DM. Down-regulation of ZnT8 expression in INS-1 rat pancreatic beta cells reduces insulin content and glucose-inducible insulin secretion. PLoS One 2009; 4:e5679. [PMID: 19479076 PMCID: PMC2682581 DOI: 10.1371/journal.pone.0005679] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2009] [Accepted: 04/30/2009] [Indexed: 11/18/2022] Open
Abstract
The SLC30A8 gene codes for a pancreatic beta-cell-expressed zinc transporter, ZnT8. A polymorphism in the SLC30A8 gene is associated with susceptibility to type 2 diabetes, although the molecular mechanism through which this phenotype is manifest is incompletely understood. Such polymorphisms may exert their effect via impacting expression level of the gene product. We used an shRNA-mediated approach to reproducibly downregulate ZnT8 mRNA expression by >90% in the INS-1 pancreatic beta cell line. The ZnT8-downregulated cells exhibited diminished uptake of exogenous zinc, as determined using the zinc-sensitive reporter dye, zinquin. ZnT8-downregulated cells showed reduced insulin content and decreased insulin secretion (expressed as percent of total insulin content) in response to hyperglycemic stimulus, as determined by insulin immunoassay. ZnT8-depleted cells also showed fewer dense-core vesicles via electron microscopy. These data indicate that reduced ZnT8 expression in cultured pancreatic beta cells gives rise to a reduced insulin response to hyperglycemia. In addition, although we provide no direct evidence, these data suggest that an SLC30A8 expression-level polymorphism could affect insulin secretion and the glycemic response in vivo.
Collapse
Affiliation(s)
- Yi Fu
- Division of Nephrology & Hypertension, Departments of Medicine, Cell and Developmental Biology, Oregon Health & Science University, Portland, Oregon, United States of America
- The Research Service, Portland V.A. Medical Center, Portland, Oregon, United States of America
| | - Wei Tian
- Division of Nephrology & Hypertension, Departments of Medicine, Cell and Developmental Biology, Oregon Health & Science University, Portland, Oregon, United States of America
- The Research Service, Portland V.A. Medical Center, Portland, Oregon, United States of America
| | - Emily B. Pratt
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon, United States of America
- Center for Research in Occupational and Environmental Toxicity, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Lisa B. Dirling
- Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon, United States of America
- Department of Pathology, Oregon Health & Science University, Portland, Oregon, United States of America
- The Research Service, Portland V.A. Medical Center, Portland, Oregon, United States of America
| | - Show-Ling Shyng
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon, United States of America
- Center for Research in Occupational and Environmental Toxicity, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Charles K. Meshul
- Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon, United States of America
- Department of Pathology, Oregon Health & Science University, Portland, Oregon, United States of America
- The Research Service, Portland V.A. Medical Center, Portland, Oregon, United States of America
| | - David M. Cohen
- Division of Nephrology & Hypertension, Departments of Medicine, Cell and Developmental Biology, Oregon Health & Science University, Portland, Oregon, United States of America
- The Research Service, Portland V.A. Medical Center, Portland, Oregon, United States of America
- * E-mail:
| |
Collapse
|
11
|
Jacobo SMP, Guerra ML, Jarrard RE, Przybyla JA, Liu G, Watts VJ, Hockerman GH. The intracellular II-III loops of Cav1.2 and Cav1.3 uncouple L-type voltage-gated Ca2+ channels from glucagon-like peptide-1 potentiation of insulin secretion in INS-1 cells via displacement from lipid rafts. J Pharmacol Exp Ther 2009; 330:283-93. [PMID: 19351867 DOI: 10.1124/jpet.109.150672] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
L-type Ca(2+) channels play a key role in the integration of physiological signals regulating insulin secretion that probably requires their localization to specific subdomains of the plasma membrane. We investigated the role of the intracellular II-III loop domains of the L-type channels Ca(v)1.2 and 1.3 in coupling of Ca(2+) influx with glucose-stimulated insulin secretion (GSIS) potentiated by the incretin hormone glucagon-like peptide (GLP)-1. In INS-1 cell lines expressing the Ca(v)1.2/II-III or Ca(v)1.3/II-III peptides, GLP-1 potentiation of GSIS was inhibited markedly, coincident with a decrease in GLP-1-stimulated cAMP accumulation and the redistribution of Ca(v)1.2 and Ca(v)1.3 out of lipid rafts. Neither the Ca(v)1.2/II-III nor the Ca(v)1.3/II-III peptide decreased L-type current density compared with untransfected INS-1 cells. GLP-1 potentiation of GSIS was restored by the L-type channel agonist 2,5-dimethyl-4-[2-(phenylmethyl)benzoyl]-1H-pyrrole-3-carboxylic acid methyl ester (FPL-64176). In contrast, potentiation of GSIS by 8-bromo-cAMP (8-Br-cAMP) was inhibited in Ca(v)1.2/II-III but not Ca(v)1.3/II-III cells. These differences may involve unique protein-protein interactions because the Ca(v)1.2/II-III peptide, but not the Ca(v)1.3/II-III peptide, immunoprecipitates Rab3-interacting molecule (RIM) 2 from INS-1 cell lysates. RIM2, and its binding partner Piccolo, localize to lipid rafts, and they may serve as anchors for Ca(v)1.2 localization to lipid rafts in INS-1 cells. These findings suggest that the II-III interdomain loops of Ca(v)1.2, and possibly Ca(v)1.3, direct these channels to membrane microdomains in which the proteins that mediate potentiation of GSIS by GLP-1 and 8-Br-cAMP assemble.
Collapse
Affiliation(s)
- Sarah Melissa P Jacobo
- Program in Biochemistry and Molecular Biology, Purdue University, West Lafayette, Indiana, USA
| | | | | | | | | | | | | |
Collapse
|
12
|
Santana LF, Navedo MF, Amberg GC, Nieves-Cintrón M, Votaw VS, Ufret-Vincenty CA. Calcium sparklets in arterial smooth muscle. Clin Exp Pharmacol Physiol 2008; 35:1121-6. [PMID: 18215181 PMCID: PMC5832963 DOI: 10.1111/j.1440-1681.2007.04867.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Voltage-dependent, L-type Ca2+ channels (LTCC) play an essential role in arterial smooth muscle contraction and, consequently, the regulation of arterial diameter, tissue perfusion and blood pressure. However, the spatial organization of functional LTCC in arterial myocytes is incompletely understood. Total internal reflection fluorescence and swept-field confocal microscopy revealed that the opening of a single or a cluster of LTCC produces local elevations in [Ca2+]i called Ca2+ sparklets. In arterial myocytes, Ca2+ sparklets are produced by the opening of Cav1.2 channels. The Ca2+ sparklet activity is bimodal. In low activity mode, rare stochastic openings of solitary LTCC produce limited Ca2+ influx ('low activity Ca2+ sparklets'). In contrast, discrete clusters of LTCC associated with protein kinase Ca (PKCa) operate in a sustained, high-activity mode resulting in substantial Ca2+ influx ('persistent Ca2+ sparklets'). The Ca2+ sparklet activity varies regionally within a myocyte depending on the relative activities of nearby PKCa and opposing protein phosphates 2A and 2B. Low- and high-activity persistent Ca2+ sparklets modulate local and global [Ca2+]i in arterial smooth muscle, suggesting that this Ca2+ signal may play an important role in the regulation of vascular function.
Collapse
Affiliation(s)
- Luis F Santana
- Department of Physiology and Biophysics, University of Washington School of Medicine, Box 357290, Seattle, WA 98195, USA.
| | | | | | | | | | | |
Collapse
|
13
|
Karl MO, Kroeger W, Wimmers S, Milenkovic VM, Valtink M, Engelmann K, Strauss O. Endogenous Gas6 and Ca2+ -channel activation modulate phagocytosis by retinal pigment epithelium. Cell Signal 2008; 20:1159-68. [PMID: 18395422 DOI: 10.1016/j.cellsig.2008.02.005] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2007] [Revised: 01/27/2008] [Accepted: 02/06/2008] [Indexed: 11/25/2022]
Abstract
Mutation or loss of MerTK as well as deficiency of alphavbeta5-integrins, gives rise to retinal-degeneration due to inefficient phagocytosis of photoreceptor outer-segment fragments by the retinal pigment epithelium (RPE). This study shows that Gas6 expressed endogenously by human RPE promotes phagocytosis. The RPE expresses Gas6 more highly in vivo and in serum-reduced conditions in vitro than in high-serum conditions, suggesting a negative-feedback control. An antibody-blockage approach revealed that Gas6-expressing RPE phagocytizes photoreceptor outer-segment fragments due to stimulation of MerTK by endogenous Gas6 in vitro. MerTK- and Gas6-antibodies reduced phagocytosis. Blocking L-type Ca(2+)-channels with nifedipine inhibited MerTK dependent phagocytosis in vitro. Application of integrin inhibitory, soluble, RGD-containing peptides or soluble vitronectin reduced L-type Ca(2+)-channel currents in RPE. Herbimycin A, which reduces phosphorylation of integrin receptor-associated proteins and decreases L-type Ca(2+)-channel currents in RPE, eliminates the inhibiting vitronectin effect and abolishes phagocytosis. Thus, Gas6-promoted phagocytosis was inhibited by L-type Ca(2+)-channel blockage, which in turn may be activated by integrin receptor stimulation. These results suggest that L-type Ca(2+)-channels could be regulated downstream of both MerTK and alphavbeta5-integrin, indicating that the binding and uptake mechanisms of phagocytosis are part of a converging pathway.
Collapse
Affiliation(s)
- Mike O Karl
- University Eye Hospital Hamburg, Martinistrasse 52, 20246 Hamburg, Germany.
| | | | | | | | | | | | | |
Collapse
|
14
|
Navedo MF, Amberg GC, Westenbroek RE, Sinnegger-Brauns MJ, Catterall WA, Striessnig J, Santana LF. Ca(v)1.3 channels produce persistent calcium sparklets, but Ca(v)1.2 channels are responsible for sparklets in mouse arterial smooth muscle. Am J Physiol Heart Circ Physiol 2007; 293:H1359-70. [PMID: 17526649 DOI: 10.1152/ajpheart.00450.2007] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ca(2+) sparklets are local elevations in intracellular Ca(2+) produced by the opening of a single or a cluster of L-type Ca(2+) channels. In arterial myocytes, Ca(2+) sparklets regulate local and global intracellular Ca(2+). At present, the molecular identity of the L-type Ca(2+) channels underlying Ca(2+) sparklets in these cells is undetermined. Here, we tested the hypotheses that voltage-gated calcium channel-alpha 1.3 subunit (Ca(v)1.3) can produce Ca(2+) sparklets and that Ca(v)1.2 and/or Ca(v)1.3 channels are responsible for Ca(2+) sparklets in mouse arterial myocytes. First, we investigated the functional properties of single Ca(v)1.3 channels in tsA201 cells. With 110 mM Ba(2+) as the charge carrier, Ca(v)1.3 channels had a conductance of 20 pS. This value is similar to that of Ca(v)1.2 and native L-type Ca(2+) channels. As previously shown for Ca(v)1.2 channels, Ca(v)1.3 channels can operate in two gating modes characterized by short and long open times. Expressed Ca(v)1.3 channels also produced Ca(2+) sparklets. Ca(v)1.3 sparklets had properties similar to those produced by Ca(v)1.2 and native L-type channels, including quantal amplitude, dihydropyridine sensitivity, bimodal gating, and dual-event duration times. However, the voltage dependencies of conductance and steady-state inactivation of the Ca(2+) current (I(Ca)) in arterial myocytes were similar to those recorded from cells expressing Ca(v)1.2 but not Ca(v)1.3 channels. Furthermore, nifedipine (10 microM) eliminated Ca(2+) sparklets in wild-type myocytes but not in myocytes expressing dihydropyridine-insensitive Ca(v)1.2 channels. Accordingly, Ca(v)1.3 transcript and protein were not detected in isolated arterial myocytes. We conclude that although Ca(v)1.3 channels can produce Ca(2+) sparklets, Ca(v)1.2 channels underlie I(Ca), Ca(2+) sparklets, and hence dihydropyridine-sensitive Ca(2+) influx in mouse arterial myocytes.
Collapse
MESH Headings
- Animals
- Calcium/metabolism
- Calcium Channel Blockers/pharmacology
- Calcium Channels, L-Type/drug effects
- Calcium Channels, L-Type/physiology
- Calcium Signaling/physiology
- Cells, Cultured
- Electrophysiology
- Mice
- Mice, Inbred C57BL
- Mice, Mutant Strains
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Myocytes, Smooth Muscle/cytology
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/metabolism
- Nifedipine/pharmacology
- Patch-Clamp Techniques
Collapse
Affiliation(s)
- Manuel F Navedo
- Department of Physiology and Biophysics, University of Washington, Box 357290, Seattle, WA 98195, USA
| | | | | | | | | | | | | |
Collapse
|
15
|
Yang SN, Berggren PO. The role of voltage-gated calcium channels in pancreatic beta-cell physiology and pathophysiology. Endocr Rev 2006; 27:621-76. [PMID: 16868246 DOI: 10.1210/er.2005-0888] [Citation(s) in RCA: 175] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Voltage-gated calcium (CaV) channels are ubiquitously expressed in various cell types throughout the body. In principle, the molecular identity, biophysical profile, and pharmacological property of CaV channels are independent of the cell type where they reside, whereas these channels execute unique functions in different cell types, such as muscle contraction, neurotransmitter release, and hormone secretion. At least six CaValpha1 subunits, including CaV1.2, CaV1.3, CaV2.1, CaV2.2, CaV2.3, and CaV3.1, have been identified in pancreatic beta-cells. These pore-forming subunits complex with certain auxiliary subunits to conduct L-, P/Q-, N-, R-, and T-type CaV currents, respectively. beta-Cell CaV channels take center stage in insulin secretion and play an important role in beta-cell physiology and pathophysiology. CaV3 channels become expressed in diabetes-prone mouse beta-cells. Point mutation in the human CaV1.2 gene results in excessive insulin secretion. Trinucleotide expansion in the human CaV1.3 and CaV2.1 gene is revealed in a subgroup of patients with type 2 diabetes. beta-Cell CaV channels are regulated by a wide range of mechanisms, either shared by other cell types or specific to beta-cells, to always guarantee a satisfactory concentration of Ca2+. Inappropriate regulation of beta-cell CaV channels causes beta-cell dysfunction and even death manifested in both type 1 and type 2 diabetes. This review summarizes current knowledge of CaV channels in beta-cell physiology and pathophysiology.
Collapse
Affiliation(s)
- Shao-Nian Yang
- The Rolf Luft Research Center for Diabetes and Endocrinology L1:03, Karolinska University Hospital Solna, SE-171 76 Stockholm, Sweden.
| | | |
Collapse
|
16
|
Manning Fox JE, Gyulkhandanyan AV, Satin LS, Wheeler MB. Oscillatory membrane potential response to glucose in islet beta-cells: a comparison of islet-cell electrical activity in mouse and rat. Endocrinology 2006; 147:4655-63. [PMID: 16857746 DOI: 10.1210/en.2006-0424] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In contrast to mouse, rat islet beta-cell membrane potential is reported not to oscillate in response to elevated glucose despite demonstrated oscillations in calcium and insulin secretion. We aim to clarify the electrical activity of rat islet beta-cells and characterize and compare the electrical activity of both alpha- and beta-cells in rat and mouse islets. We recorded electrical activity from alpha- and beta-cells within intact islets from both mouse and rat using the perforated whole-cell patch clamp technique. Fifty-six percent of both mouse and rat beta-cells exhibited an oscillatory response to 11.1 mm glucose. Responses to both 11.1 mm and 2.8 mm glucose were identical in the two species. Rat beta-cells exhibited incremental depolarization in a glucose concentration-dependent manner. We also demonstrated electrical activity in human islets recorded under the same conditions. In both mouse and rat alpha-cells 11 mm glucose caused hyperpolarization of the membrane potential, whereas 2.8 mm glucose produced action potential firing. No species differences were observed in the response of alpha-cells to glucose. This paper is the first to demonstrate and characterize oscillatory membrane potential fluctuations in the presence of elevated glucose in rat islet beta-cells in comparison with mouse. The findings promote the use of rat islets in future electrophysiological studies, enabling consistency between electrophysiological and insulin secretion studies. An inverse response of alpha-cell membrane potential to glucose furthers our understanding of the mechanisms underlying glucose sensitive glucagon secretion.
Collapse
|
17
|
Liu G, Jacobo SMP, Hilliard N, Hockerman GH. Differential modulation of Cav1.2 and Cav1.3-mediated glucose-stimulated insulin secretion by cAMP in INS-1 cells: distinct roles for exchange protein directly activated by cAMP 2 (Epac2) and protein kinase A. J Pharmacol Exp Ther 2006; 318:152-60. [PMID: 16565168 DOI: 10.1124/jpet.105.097477] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Using insulin-secreting cell line (INS)-1 cells stably expressing dihydropyridine-insensitive mutants of either Cav1.2 or Cav1.3, we previously demonstrated that Cav1.3 is preferentially coupled to insulin secretion and [Ca2+]i oscillations stimulated by 11.2 mM glucose. Using the same system, we found that insulin secretion in 7.5 mM glucose plus 1 mM 8-bromo-cAMP (8-Br-cAMP) is mediated by both Cav1.2 and Cav1.3. Treatment of INS-1 cells or INS-1 cells stably expressing Cav1.2/dihydropyridine-insensitive (DHPi) channels in the presence of 10 microM nifedipine, with effector-specific cAMP analogs 8-(4-chlorophenylthio)-2'-O-methyladenosine-cAMP [8-pCPT-2'-O-Me-cAMP; 100 microM; Exchange Protein directly Activated by cAMP 2 (Epac2)-selective] or N6-benzoyl-cAMP [50 microM; Protein Kinase A (PKA)-selective] partially increased insulin secretion. Secretion stimulated by a combination of the two cAMP analogs was additive and comparable with that stimulated by 1 mM 8-Br-cAMP. In INS-1 cells stably expressing Cav1.3/DHPi in the presence of 10 microM nifedipine, N6-benzoyl-cAMP, but not 8-pCPT-2'-O-Me-cAMP, significantly increased glucose-stimulated insulin secretion. However, the combination of N6-benzoyl-cAMP and 8-pCPT-2'-O-Me-cAMP significantly increased glucose-stimulated secretion compared with N6-benzoyl-cAMP alone. In INS-1 cells, 8-Br-cAMP potentiation of insulin secretion in 7.5 mM glucose is blocked by thapsigargin (1 microM) and ryanodine (0.5 microM). In contrast, ryanodine has no effect on insulin secretion or [Ca2+]i oscillations stimulated by 11.2 mM glucose in INS-1 cells. Our data suggest that both Cav1.2 and Cav1.3 mediate insulin secretion stimulated by 7.5 mM glucose and cAMP via a mechanism that requires internal stores of Ca2+. Furthermore, cAMP modulation of secretion mediated by Cav1.2 seems to involve both Epac2 and PKA independently. In contrast, cAMP modulation of Cav1.3-mediated secretion depends upon PKA activation, whereas the contribution of Epac2 is dependent upon PKA activation.
Collapse
Affiliation(s)
- Guohong Liu
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, 575 Stadium Mall Drive, West Lafayette, IN 47907-2091, USA
| | | | | | | |
Collapse
|
18
|
Abstract
L-type calcium channels couple membrane depolarization in neurons to numerous processes including gene expression, synaptic efficacy, and cell survival. To establish the contribution of L-type calcium channels to various signaling cascades, investigators have relied on their unique pharmacological sensitivity to dihydropyridines. The traditional view of dihydropyridine-sensitive L-type calcium channels is that they are high-voltage–activating and have slow activation kinetics. These properties limit the involvement of L-type calcium channels to neuronal functions triggered by strong and sustained depolarizations. This review highlights literature, both long-standing and recent, that points to significant functional diversity among L-type calcium channels expressed in neurons and other excitable cells. Past literature contains several reports of low-voltage–activated neuronal L-type calcium channels that parallel the unique properties of recently cloned CaV1.3 L-type channels. The fast kinetics and low activation thresholds of CaV1.3 channels stand in stark contrast to criteria currently used to describe L-type calcium channels. A more accurate view of neuronal L-type calcium channels encompasses a broad range of activation thresholds and recognizes their potential contribution to signaling cascades triggered by subthreshold depolarizations.
Collapse
Affiliation(s)
- Diane Lipscombe
- Department of Neuroscience, Brown University, 190 Thayer Street, Providence, RI 02912, USA.
| | | | | |
Collapse
|