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Cai SY, Yu D, Soroka CJ, Wang J, Boyer JL. Hepatic NFAT signaling regulates the expression of inflammatory cytokines in cholestasis. J Hepatol 2021; 74:550-559. [PMID: 33039404 PMCID: PMC7897288 DOI: 10.1016/j.jhep.2020.09.035] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/24/2020] [Revised: 09/18/2020] [Accepted: 09/24/2020] [Indexed: 12/14/2022]
Abstract
BACKGROUND & AIMS The nuclear factor of activated T-cells (NFAT) plays an important role in immune responses by regulating the expression of inflammatory genes. However, it is not known whether NFAT plays any role in the bile acid (BA)-induced hepatic inflammatory response. Thus, we aimed to examine the functional role of NFATc3 in cholestatic liver injury in mice and humans. METHODS Gene and protein expression and cellular localization were assessed in primary hepatocyte cultures (mouse and human) and cholestatic liver tissues (murine models and patients with primary biliary cholangitis [PBC] or primary sclerosing cholangitis [PSC]) by quantitative PCR, western blot and immunohistochemistry. Specific NFAT inhibitors were used in vivo and in vitro. Gene reporter assays and ChIP-PCR were used to determine promoter activity. RESULTS NFAT isoforms c1 and c3 were expressed in human and mouse hepatocytes. When treated with cholestatic levels of BAs, nuclear translocation of NFATc3 was increased in both human and mouse hepatocytes and was associated with elevated mRNA levels of IL-8, CXCL2, and CXCL10 in these cells. Blocking NFAT activation with pathway-specific inhibitors or knocking down Nfatc3 expression significantly decreased BA-driven induction of these cytokines in mouse hepatocytes. Nuclear expression of NFATc3/Nfatc3 protein was increased in cholestatic livers, both in mouse models (bile duct ligation or Abcb4-/- mice) and in patients with PBC and PSC in association with elevated tissue levels of Cxcl2 (mice) or IL-8 (humans). Gene reporter assays and ChIP-PCR demonstrated that the NFAT response element in the IL-8 promoter played a key role in BA-induced human IL-8 expression. Finally, blocking NFAT activation in vivo in Abcb4-/- mice reduced cholestatic liver injury. CONCLUSIONS NFAT plays an important role in BA-stimulated hepatic cytokine expression in cholestasis. Blocking hepatic NFAT activation may reduce cholestatic liver injury in humans. LAY SUMMARY Bile acid induces liver injury by stimulating the expression of inflammatory genes in hepatocytes through activation of the transcription factor NFAT. Blocking this activation in vitro (in hepatocyte cultures) and in vivo (in cholestatic mice) decreased the expression of inflammatory genes and reduced liver injury.
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Affiliation(s)
- Shi-Ying Cai
- Department of Internal Medicine, Liver Center, Yale University School of Medicine, New Haven, CT 06520.
| | - Dongke Yu
- Department of Internal Medicine, Liver Center, Yale University School of Medicine, New Haven, CT 06520
| | - Carol J Soroka
- Department of Internal Medicine, Liver Center, Yale University School of Medicine, New Haven, CT 06520
| | - Jing Wang
- Department of Internal Medicine, Liver Center, Yale University School of Medicine, New Haven, CT 06520
| | - James L Boyer
- Department of Internal Medicine, Liver Center, Yale University School of Medicine, New Haven, CT 06520.
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Penman SL, Sharma P, Aerts H, Park BK, Weaver RJ, Chadwick AE. Differential toxic effects of bile acid mixtures in isolated mitochondria and physiologically relevant HepaRG cells. Toxicol In Vitro 2019; 61:104595. [PMID: 31288073 PMCID: PMC6853172 DOI: 10.1016/j.tiv.2019.104595] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Revised: 07/05/2019] [Accepted: 07/05/2019] [Indexed: 12/19/2022]
Abstract
Bile acids (BAs) are recognised as the causative agents of toxicity in drug-induced cholestasis (DIC). Research in isolated mitochondria and HepG2 cells have demonstrated BA-mediated mitochondrial dysfunction as a key mechanism of toxicity in DIC. However, HepG2 cells are of limited suitability for DIC studies as they do not express the necessary physiological characteristics. In this study, the mitotoxic potentials of BA mixtures were assessed in isolated mitochondria and a better-suited hepatic model, HepaRG cells. BAs induced structural alterations and a loss of mitochondrial membrane potential (MMP) in isolated mitochondria however, this toxicity did not translate to HepaRG cells. There were no changes in oxygen consumption rate, MMP or ATP levels in glucose and galactose media, indicating that there was no direct mitochondrial toxicity mediated via electron transport chain dysfunction in HepaRG cells. Assessment of key biliary transporters revealed that there was a time-dependent reduction in the expression and activity of multi-drug resistance protein 2 (MRP2), which was consistent with the induction of cytotoxicity in HepaRG cells. Overall, the findings from this study have demonstrated that mitochondrial dysfunction is not a mechanism of BA-induced toxicity in HepaRG cells. HepaRG cells are a better suited in vitro model for cholestatic studies than HepG2 cell. Bile acids cause mitochondrial toxicity in isolated mitochondria but not in HepaRG cells. Time-dependent alterations in biliary transporters are consistent with the cytotoxicity of bile acid mixtures. There are important mechanistic differences when bile acids interact at the organelle level versus the whole cell.
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Affiliation(s)
- Sophie L Penman
- MRC Centre for Drug Safety Science, Department of Molecular and Clinical Pharmacology, University of Liverpool, Liverpool L69 3GE, UK
| | - Parveen Sharma
- MRC Centre for Drug Safety Science, Department of Molecular and Clinical Pharmacology, University of Liverpool, Liverpool L69 3GE, UK
| | - Hélène Aerts
- Biologie Servier, 905 Rue de Saran, 45520 Gidy, France
| | - B Kevin Park
- MRC Centre for Drug Safety Science, Department of Molecular and Clinical Pharmacology, University of Liverpool, Liverpool L69 3GE, UK
| | - Richard J Weaver
- Institute de Recherches Internationales Servier, Biopharmacy, rue Carnot, 92284 Suresnes, France
| | - Amy E Chadwick
- MRC Centre for Drug Safety Science, Department of Molecular and Clinical Pharmacology, University of Liverpool, Liverpool L69 3GE, UK.
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3
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Abstract
Cholestasis is a common pathological component of numerous liver diseases. The initiating event during cholestatic liver injury is widely believed to be the accumulation of bile acids in hepatocytes and the hepatic parenchyma. As bile acids are considered the primary toxic compounds in the injury, numerous in vitro models of bile acid-induced injury and bile acid-induced changes in gene expression have been developed to attempt to better define cholestasis at a cellular level. This chapter focuses on the establishment of a system for determining the effects of cholestatic concentrations of bile acids on hepatocytes using primary hepatocytes or hepatoma cell lines. Moreover, this chapter addresses significant differences in the response of different species to bile acid exposure and novel information on the relevance of treating hepatocytes with concentrations of specific bile acids.
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Ye J, Rozdeba PJ, Morone UI, Daou A, Abarbanel HDI. Estimating the biophysical properties of neurons with intracellular calcium dynamics. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:062714. [PMID: 25019821 DOI: 10.1103/physreve.89.062714] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2014] [Indexed: 06/03/2023]
Abstract
We investigate the dynamics of a conductance-based neuron model coupled to a model of intracellular calcium uptake and release by the endoplasmic reticulum. The intracellular calcium dynamics occur on a time scale that is orders of magnitude slower than voltage spiking behavior. Coupling these mechanisms sets the stage for the appearance of chaotic dynamics, which we observe within certain ranges of model parameter values. We then explore the question of whether one can, using observed voltage data alone, estimate the states and parameters of the voltage plus calcium (V+Ca) dynamics model. We find the answer is negative. Indeed, we show that voltage plus another observed quantity must be known to allow the estimation to be accurate. We show that observing both the voltage time course V(t) and the intracellular Ca time course will permit accurate estimation, and from the estimated model state, accurate prediction after observations are completed. This sets the stage for how one will be able to use a more detailed model of V+Ca dynamics in neuron activity in the analysis of experimental data on individual neurons as well as functional networks in which the nodes (neurons) have these biophysical properties.
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Affiliation(s)
- Jingxin Ye
- Department of Physics, University of California, San Diego, La Jolla, California 92093-0374, USA
| | - Paul J Rozdeba
- Department of Physics, University of California, San Diego, La Jolla, California 92093-0374, USA
| | - Uriel I Morone
- Department of Physics, University of California, San Diego, La Jolla, California 92093-0374, USA
| | - Arij Daou
- Department of Organismal Biology and Anatomy, University of Chicago, Chicago, Illinois 60647, USA
| | - Henry D I Abarbanel
- Department of Physics and Marine Physical Laboratory (Scripps Institution of Oceanography) University of California, San Diego La Jolla, California 92093-0374, USA
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5
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Aromataris EC, Castro J, Rychkov GY, Barritt GJ. Store-operated Ca(2+) channels and Stromal Interaction Molecule 1 (STIM1) are targets for the actions of bile acids on liver cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1783:874-85. [PMID: 18342630 DOI: 10.1016/j.bbamcr.2008.02.011] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2007] [Revised: 02/07/2008] [Accepted: 02/11/2008] [Indexed: 12/18/2022]
Abstract
Cholestasis is a significant contributor to liver pathology and can lead to primary sclerosis and liver failure. Cholestatic bile acids induce apoptosis and necrosis in hepatocytes but these effects can be partially alleviated by the pharmacological application of choleretic bile acids. These actions of bile acids on hepatocytes require changes in the release of Ca(2+) from intracellular stores and in Ca(2+) entry. However, the nature of the Ca(2+) entry pathway affected is not known. We show here using whole cell patch clamp experiments with H4-IIE liver cells that taurodeoxycholic acid (TDCA) and other choleretic bile acids reversibly activate an inwardly-rectifying current with characteristics similar to those of store-operated Ca(2+) channels (SOCs), while lithocholic acid (LCA) and other cholestatic bile acids inhibit SOCs. The activation of Ca(2+) entry was observed upon direct addition of the bile acid to the incubation medium, whereas the inhibition of SOCs required a 12 h pre-incubation. In cells loaded with fura-2, choleretic bile acids activated a Gd(3+)-inhibitable Ca(2+) entry, while cholestatic bile acids inhibited the release of Ca(2+) from intracellular stores and Ca(2+) entry induced by 2,5-di-(tert-butyl)-1,4-benzohydro-quinone (DBHQ). TDCA and LCA each caused a reversible redistribution of stromal interaction molecule 1 (STIM1, the endoplasmic reticulum Ca(2+) sensor required for the activation of Ca(2+) release-activated Ca(2+) channels and some other SOCs) to puncta, similar to that induced by thapsigargin. Knockdown of Stim1 using siRNA caused substantial inhibition of Ca(2+)-entry activated by choleretic bile acids. It is concluded that choleretic and cholestatic bile acids activate and inhibit, respectively, the previously well-characterised Ca(2+)-selective hepatocyte SOCs through mechanisms which involve the bile acid-induced redistribution of STIM1.
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Affiliation(s)
- Edoardo C Aromataris
- School of Molecular and Biomedical Science, University of Adelaide, Adelaide, SA, Australia
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6
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Borghans JM, Dupont G, Goldbeter A. Complex intracellular calcium oscillations. A theoretical exploration of possible mechanisms. Biophys Chem 2007; 66:25-41. [PMID: 17029867 DOI: 10.1016/s0301-4622(97)00010-0] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/1996] [Revised: 01/13/1997] [Accepted: 01/16/1997] [Indexed: 11/16/2022]
Abstract
Intracellular Ca(2+) oscillations are commonly observed in a large number of cell types in response to stimulation by an extracellular agonist. In most cell types the mechanism of regular spiking is well understood and models based on Ca(2+)-induced Ca(2+) release (CICR) can account for many experimental observations. However, cells do not always exhibit simple Ca(2+) oscillations. In response to given agonists, some cells show more complex behaviour in the form of bursting, i.e. trains of Ca(2+) spikes separated by silent phases. Here we develop several theoretical models, based on physiologically plausible assumptions, that could account for complex intracellular Ca(2+) oscillations. The models are all based on one- or two-pool models based on CICR. We extend these models by (i) considering the inhibition of the Ca(2+)-release channel on a unique intracellular store at high cytosolic Ca(2+) concentrations, (ii) taking into account the Ca(2+)-activated degradation of inositol 1,4,5-trisphosphate (IP(3)), or (iii) considering explicity the evolution of the Ca(2+) concentration in two different pools, one sensitive and the other one insensitive to IP(3). Besides simple periodic oscillations, these three models can all account for more complex oscillatory behaviour in the form of bursting. Moreover, the model that takes the kinetics of IP(3) into account shows chaotic behaviour.
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Affiliation(s)
- J M Borghans
- Faculté des Sciences, Université Libre de Bruxelles, Campus Plaine, C.P. 231, B-1050 Brussels, Belgium
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Zhu CL, Jia Y, Liu Q, Yang LJ, Zhan X. A mesoscopic stochastic mechanism of cytosolic calcium oscillations. Biophys Chem 2007; 125:201-12. [PMID: 16952419 DOI: 10.1016/j.bpc.2006.08.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2006] [Revised: 08/01/2006] [Accepted: 08/02/2006] [Indexed: 10/24/2022]
Abstract
Based on a model of intracellular calcium (Ca(2+)) oscillation with self-modulation of inositol 1,4,5-trisphosphate signal, the mesoscopic stochastic differential equations for the intracellular Ca(2+) oscillations are theoretically derived by using the chemical Langevin equation method. The effects of the finite biochemical reaction molecule number on both simple and complex cytosolic Ca(2+) oscillations are numerically studied. In the case of simple intracellular Ca(2+) oscillation, it is found that, with the increase of molecule number, the coherence resonance or autonomous resonance phenomena can occur for some external stimulation parameter values. In the cases of complex cytosolic Ca(2+) oscillations, each extremum of concentration of cytosolic Ca(2+) oscillations corresponds to a peak in the histogram of Ca(2+) concentration, and the most probability appeared during the bursting plateau level for bursting, but at the largest minimum of Ca(2+) concentration for chaos. For quasi-periodicity, however, there are only two peaks in the histogram of Ca(2+) concentration, and the most probability is located at low concentration state.
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Affiliation(s)
- Chun-Lian Zhu
- Department of Physics, Jianghan University, Wuhan 430056, China
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Abstract
Cholangiocytes are exposed to high concentrations of bile acids at their apical membrane. A selective transporter for bile acids, the Apical Sodium Bile Acid Cotransporter (ASBT) (also referred to as Ibat; gene name Slc10a2) is localized on the cholangiocyte apical membrane. On the basolateral membrane, four transport systems have been identified (t-ASBT, multidrug resistance (MDR)3, an unidentified anion exchanger system and organic solute transporter (Ost) heteromeric transporter, Ostα-Ostβ. Together, these transporters unidirectionally move bile acids from ductal bile to the circulation. Bile acids absorbed by cholangiocytes recycle via the peribiliary plexus back to hepatocytes for re-secretion into bile. This recycling of bile acids between hepatocytes and cholangiocytes is referred to as the cholehepatic shunt pathway. Recent studies suggest that the cholehepatic shunt pathway may contribute in overall hepatobiliary transport of bile acids and to the adaptation to chronic cholestasis due to extrahepatic obstruction. ASBT is acutely regulated by an adenosine 3', 5’-monophosphate (cAMP)-dependent translocation to the apical membrane and by phosphorylation-dependent ubiquitination and proteasome degradation. ASBT is chronically regulated by changes in gene expression in response to biliary bile acid concentration and inflammatory cytokines. Another potential function of cholangiocyte ASBT is to allow cholangiocytes to sample biliary bile acids in order to activate intracellular signaling pathways. Bile acids trigger changes in intracellular calcium, protein kinase C (PKC), phosphoinositide 3-kinase (PI3K), mitogen-activated protein (MAP) kinase and extracellular signal-regulated protein kinase (ERK) intracellular signals. Bile acids significantly alter cholangiocyte secretion, proliferation and survival. Different bile acids have differential effects on cholangiocyte intracellular signals, and in some instances trigger opposing effects on cholangiocyte secretion, proliferation and survival. Based upon these concepts and observations, the cholangiocyte has been proposed to be the principle target cell for bile acids in the liver.
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Affiliation(s)
- Xuefeng Xia
- University of Texas at Houston Medical School, 6431 Fannin Street, MSB 4.234, Houston TX 77030, USA
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9
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Perc M, Gosak M, Marhl M. From stochasticity to determinism in the collective dynamics of diffusively coupled cells. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2006.01.065] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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10
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Larsen AZ, Olsen LF, Kummer U. On the encoding and decoding of calcium signals in hepatocytes. Biophys Chem 2004; 107:83-99. [PMID: 14871603 DOI: 10.1016/j.bpc.2003.08.010] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2003] [Revised: 08/25/2003] [Accepted: 08/25/2003] [Indexed: 11/24/2022]
Abstract
Many different agonists use calcium as a second messenger. Despite intensive research in intracellular calcium signalling it is an unsolved riddle how the different types of information represented by the different agonists, is encoded using the universal carrier calcium. It is also still not clear how the information encoded is decoded again into the intracellular specific information at the site of enzymes and genes. After the discovery of calcium oscillations, one likely mechanism is that information is encoded in the frequency, amplitude and waveform of the oscillations. This hypothesis has received some experimental support. However, the mechanism of decoding of oscillatory signals is still not known. Here, we study a mechanistic model of calcium oscillations, which is able to reproduce both spiking and bursting calcium oscillations. We use the model to study the decoding of calcium signals on the basis of co-operativity of calcium binding to various proteins. We show that this co-operativity offers a simple way to decode different calcium dynamics into different enzyme activities.
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Affiliation(s)
- Ann Zahle Larsen
- Celcom, Department of Biochemistry and Molecular Biology, Syddansk Universitet, Campusvej 55, Odense M DK-5230, Denmark.
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11
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Rozi A, Jia Y. A theoretical study of effects of cytosolic Ca2+ oscillations on activation of glycogen phosphorylase. Biophys Chem 2004; 106:193-202. [PMID: 14556891 DOI: 10.1016/s0301-4622(03)00192-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Taking into account the Ca(2+)-stimulated degradation of inositol 1,4,5-trisphosphate (IP(3)) by a 3-kinase, we have theoretically explored the effects of both simple and complex Ca(2+) oscillations on the regulation of a phosphorylation-dephosphorylation cycle process involved in glycogen degradation by glycogen phosphorylase a-form, respectively. For the case of simple Ca(2+) oscillations, the roles of cytosolic Ca(2+) oscillations in the regulation of active phosphorylase depend upon the maximum rate of IP(3) degradation by the 3-kinase, V(M5). In particular, the smaller the values of V(M5) are, the lower the effective Ca(2+) threshold for the activation of glycogen phosphorylase will be. For the case of complex Ca(2+) oscillations, the average level of fraction of active phosphorylase is nearly independent from the level of stimulation increasing in the bursting oscillatory domain. Both simple and complex Ca(2+) oscillations can contribute to increase the efficiency and specificity of cellular signalling, and some theoretical results of activation of glycogen phosphorylase regulated by Ca(2+) oscillations are close to the experimental results for gene expression in lymphocytes.
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Affiliation(s)
- Anvar Rozi
- Department of Physics, Central China Normal University, Wuhan 430079, Hubei, PR China
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12
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Camello C, Lomax R, Petersen OH, Tepikin AV. Calcium leak from intracellular stores--the enigma of calcium signalling. Cell Calcium 2002; 32:355-61. [PMID: 12543095 DOI: 10.1016/s0143416002001926] [Citation(s) in RCA: 137] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Wherever you travel through the cytoplasm of the cells you will find organelles with internal [Ca(2+)] levels higher than in the surrounding cytosol. This is particularly true of the endoplasmic reticulum (ER) (or sarcoplasmic reticulum (SR) in muscle cells); such organelles serve as the main sources of releasable Ca(2+) for cytosolic cellular signalling. Calcium pumps of the SERCA family (sarcoplasmic and endoplasmic reticulum calcium ATP-ases) import calcium into the organelle lumen. The other mechanism that is responsible for the steady state calcium level within the lumen of ER or SR is a calcium leak that balances the influx created by the pumps. The leak remains the most enigmatic of the processes involved in calcium regulation. The molecular nature of the leak mechanism is not known. The basal leak is a relatively slow process, which is difficult to investigate and which is easily outmatched (both in the amplitude of calcium responses and in attractiveness to experimenters) by substantially faster second messenger-induced release. Nevertheless, information on the properties of the calcium leak, although thinly scattered through the pages of PubMed, has been slowly accumulating. In this review we will discuss the properties of the calcium leak and speculate about possible mechanisms, which could mediate this process.
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Affiliation(s)
- C Camello
- The Physiological Laboratory, The University of Liverpool, Crown Street, L69 3BX, Liverpool, UK
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Voronina S, Longbottom R, Sutton R, Petersen OH, Tepikin A. Bile acids induce calcium signals in mouse pancreatic acinar cells: implications for bile-induced pancreatic pathology. J Physiol 2002; 540:49-55. [PMID: 11927668 PMCID: PMC2290202 DOI: 10.1113/jphysiol.2002.017525] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The effect of the natural bile acid, taurolithocholic acid 3-sulfate (TLC-S), on calcium signalling in pancreatic acinar cells has been investigated. TLC-S induced global calcium oscillations and extended calcium transients as well as calcium signals localised to the secretory granule (apical) region of acinar cells. These calcium signals could still be triggered by TLC-S in a calcium-free external solution. TLC-S-induced calcium signals were not inhibited by atropine, but were abolished by caffeine or by depletion of calcium stores, due to prolonged application of ACh. Global calcium signals, produced by TLC-S application, displayed vectorial apical-to-basal polarity. The signals originated in the apical part and were then propagated to the basal region. Other natural bile acids, taurocholate (TC) and taurodeoxycholate (TDC), were also able to produce local and global calcium oscillations (but at higher concentrations than TLC-S). Bile, which can enter pancreas by reflux, has been implicated in the pathology of acute pancreatitis. The calcium releasing properties of bile acids suggest that calcium toxicity could be an important contributing factor in the bile acid-induced cellular damage.
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Affiliation(s)
- Svetlana Voronina
- The Physiological Laboratory, The University of Liverpool, Crown Street, Liverpool L69 3BX, UK
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14
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Haberichter T, Marhl M, Heinrich R. Birhythmicity, trirhythmicity and chaos in bursting calcium oscillations. Biophys Chem 2001; 90:17-30. [PMID: 11321672 DOI: 10.1016/s0301-4622(01)00127-2] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
We have analyzed various types of complex calcium oscillations. The oscillations are explained with a model based on calcium-induced calcium release (CICR). In addition to the endoplasmic reticulum as the main intracellular Ca2+ store, mitochondrial and cytosolic Ca2+ binding proteins are also taken into account. This model was previously proposed for the study of the physiological role of mitochondria and the cytosolic proteins in gene rating complex Ca2+ oscillations [1]. Here, we investigated the occurrence of different types of Ca2+ oscillations obtained by the model, i.e. simple oscillations, bursting, and chaos. In a bifurcation diagram, we have shown that all these various modes of oscillatory behavior are obtained by a change of only one model parameter, which corresponds to the physiological variability of an agonist. Bursting oscillations were studied in more detail because they express birhythmicity, trirhythmicity and chaotic behavior. Two different routes to chaos are observed in the model: in addition to the usual period doubling cascade, we also show intermittency. For the characterization of the chaotic behavior, we made use of return maps and Lyapunov exponents. The potential biological role of chaos in intracellular signaling is discussed.
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Affiliation(s)
- T Haberichter
- Humboldt University Berlin, Institute of Biology, Theoretical Biophysics, Germany.
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15
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Abstract
Bile acids, which are synthesized in the liver from cholesterol, are important in the production of bile flow, excretion of cholesterol, and intestinal digestion and absorption of fats and fat-soluble vitamins. Increases and/or alterations in concentrations of bile acids in serum are specific and sensitive indicators of hepatobiliary disorders. Synthesis of bile acids in hepatocytes involves steps in endoplasmic reticulum, cytosol, mitochondria, and peroxisomes. Other important hepatocellular processes involving bile acids include active uptake by the basolateral membrane, intracellular transport, P-450-mediated conjugations and hydroxylations, and canalicular secretion. Hydrophobic bile acids produce hepatotoxicity in vivo and in vitro. In experimental and epidemiologic studies, some of these forms have been identified as causative agents in the development of colon and liver (experimental only) cancer. Conversely, several hydrophilic forms, primarily ursodeoxycholic acid, have demonstrated cytoprotective properties in a variety of clinical and experimental hepatobiliary diseases and disorders. Because bile acids can have dramatically different properties and effects, determination of mechanisms of action of these compounds has become an active area of research. Primary isolated hepatocytes provide an opportunity to investigate bile acid-related functions and effects in well-designed, carefully controlled studies. Short-term cultures have been used to study a variety of issues related to bile acids, including cytotoxicity, synthesis, and hepatocellular processing. With these systems, however, many functions of mature hepatocytes, including those pertaining to bile acids, can be lost when cultures are maintained for more than several days. Recent developments in culture techniques permit long-term maintenance of functionally stable, differentiated cells. Pertaining to bile acid research, these systems remain to be fully characterized but, in appropriate situations, they should provide important alternatives to in vivo studies and short-term in vitro assays.
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Affiliation(s)
- M B Thompson
- Laboratory of Experimental Pathology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA
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