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Miller RA, Shi Y, Lu W, Pirman DA, Jatkar A, Blatnik M, Wu H, Cárdenas C, Wan M, Foskett JK, Park JO, Zhang Y, Holland WL, Rabinowitz JD, Birnbaum MJ. Targeting hepatic glutaminase activity to ameliorate hyperglycemia. Nat Med 2018; 24:518-524. [PMID: 29578539 PMCID: PMC6089616 DOI: 10.1038/nm.4514] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Accepted: 02/08/2018] [Indexed: 02/07/2023]
Affiliation(s)
- Russell A Miller
- Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.,Pfizer Internal Medicine Research Units, Cambridge, Massachusetts, USA
| | - Yuji Shi
- Pfizer Internal Medicine Research Units, Cambridge, Massachusetts, USA
| | - Wenyun Lu
- Chemistry and Integrative Genomics, Princeton University, Princeton, New Jersey, USA
| | - David A Pirman
- Pfizer Worldwide Research and Development, Groton, Connecticut, USA
| | - Aditi Jatkar
- Pfizer Internal Medicine Research Units, Cambridge, Massachusetts, USA
| | - Matthew Blatnik
- Pfizer Worldwide Research and Development, Groton, Connecticut, USA
| | - Hong Wu
- Pfizer Worldwide Research and Development, Groton, Connecticut, USA
| | - César Cárdenas
- Anatomy and Developmental Biology Program, Institute of Biomedical Sciences, University of Chile, Santiago, Chile.,Geroscience Center for Brain Health and Metabolism, Santiago, Chile.,Buck Institute for Research on Aging, Novato, California, USA.,Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, California, USA
| | - Min Wan
- Pfizer Internal Medicine Research Units, Cambridge, Massachusetts, USA
| | - J Kevin Foskett
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.,Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Junyoung O Park
- Chemistry and Integrative Genomics, Princeton University, Princeton, New Jersey, USA.,Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey, USA
| | - Yiyi Zhang
- Touchstone Diabetes Center, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - William L Holland
- Touchstone Diabetes Center, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Joshua D Rabinowitz
- Chemistry and Integrative Genomics, Princeton University, Princeton, New Jersey, USA
| | - Morris J Birnbaum
- Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.,Pfizer Internal Medicine Research Units, Cambridge, Massachusetts, USA.,Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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Zhang B, Crankshaw W, Nesemeier R, Patel J, Nweze I, Lakshmanan J, Harbrecht BG. Calcium-mediated signaling and calmodulin-dependent kinase regulate hepatocyte-inducible nitric oxide synthase expression. J Surg Res 2014; 193:795-801. [PMID: 25150084 DOI: 10.1016/j.jss.2014.07.042] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Revised: 07/14/2014] [Accepted: 07/18/2014] [Indexed: 02/07/2023]
Abstract
BACKGROUND Induced nitric oxide synthase (iNOS) is induced in hepatocytes by shock and inflammatory stimuli. Excessive NO from iNOS mediates shock-induced hepatic injury and death, so understanding the regulation of iNOS will help elucidate the pathophysiology of septic shock. In vitro, cytokines induce iNOS expression through activation of signaling pathways including mitogen-activated protein kinases and nuclear factor κB. Cytokines also induce calcium (Ca(2+)) mobilization and activate calcium-mediated intracellular signaling pathways, typically through activation of calmodulin-dependent kinases (CaMK). Calcium regulates NO production in macrophages but the role of calcium and calcium-mediated signaling in hepatocyte iNOS expression has not been defined. MATERIALS AND METHODS Primary rat hepatocytes were isolated, cultured, and induced to produce NO with proinflammatory cytokines. Calcium mobilization and Ca(2+)-mediated signaling were altered with ionophore, Ca(2+) channel blockers, and inhibitors of CaMK. RESULTS The Ca(2+) ionophore A23187 suppressed cytokine-stimulated NO production, whereas Ethylene glycol tetraacetic acid and nifedipine increased NO production, iNOS messenger RNA, and iNOS protein expression. Inhibition of CaMK with KN93 and CBD increased NO production but the calcineurin inhibitor FK 506 decreased iNOS expression. CONCLUSIONS These data demonstrate that calcium-mediated signaling regulates hepatocyte iNOS expression and does so through a mechanism independent of calcineurin. Changes in intracellular calcium levels may regulate iNOS expression during hepatic inflammation induced by proinflammatory cytokines.
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Affiliation(s)
- Baochun Zhang
- The Hiram C. Polk, Jr. MD Department of Surgery, the Price Institute for Surgical Research, University of Louisville, Louisville, Kentucky
| | - Will Crankshaw
- The Hiram C. Polk, Jr. MD Department of Surgery, the Price Institute for Surgical Research, University of Louisville, Louisville, Kentucky
| | - Ryan Nesemeier
- The Hiram C. Polk, Jr. MD Department of Surgery, the Price Institute for Surgical Research, University of Louisville, Louisville, Kentucky
| | - Jay Patel
- The Hiram C. Polk, Jr. MD Department of Surgery, the Price Institute for Surgical Research, University of Louisville, Louisville, Kentucky
| | - Ikenna Nweze
- The Hiram C. Polk, Jr. MD Department of Surgery, the Price Institute for Surgical Research, University of Louisville, Louisville, Kentucky
| | - Jaganathan Lakshmanan
- The Hiram C. Polk, Jr. MD Department of Surgery, the Price Institute for Surgical Research, University of Louisville, Louisville, Kentucky
| | - Brian G Harbrecht
- The Hiram C. Polk, Jr. MD Department of Surgery, the Price Institute for Surgical Research, University of Louisville, Louisville, Kentucky.
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Ca(2+) -permeable channels in the hepatocyte plasma membrane and their roles in hepatocyte physiology. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1783:651-72. [PMID: 18291110 DOI: 10.1016/j.bbamcr.2008.01.016] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2007] [Revised: 01/16/2008] [Accepted: 01/17/2008] [Indexed: 01/24/2023]
Abstract
Hepatocytes are highly differentiated and spatially polarised cells which conduct a wide range of functions, including intermediary metabolism, protein synthesis and secretion, and the synthesis, transport and secretion of bile acids. Changes in the concentrations of Ca(2+) in the cytoplasmic space, endoplasmic reticulum (ER), mitochondria, and other intracellular organelles make an essential contribution to the regulation of these hepatocyte functions. While not yet fully understood, the spatial and temporal parameters of the cytoplasmic Ca(2+) signals and the entry of Ca(2+) through Ca(2+)-permeable channels in the plasma membrane are critical to the regulation by Ca(2+) of hepatocyte function. Ca(2+) entry across the hepatocyte plasma membrane has been studied in hepatocytes in situ, in isolated hepatocytes and in liver cell lines. The types of Ca(2+)-permeable channels identified are store-operated, ligand-gated, receptor-activated and stretch-activated channels, and these may vary depending on the animal species studied. Rat liver cell store-operated Ca(2+) channels (SOCs) have a high selectivity for Ca(2+) and characteristics similar to those of the Ca(2+) release activated Ca(2+) channels in lymphocytes and mast cells. Liver cell SOCs are activated by a decrease in Ca(2+) in a sub-region of the ER enriched in type1 IP(3) receptors. Activation requires stromal interaction molecule type 1 (STIM1), and G(i2alpha,) F-actin and PLCgamma1 as facilitatory proteins. P(2x) purinergic channels are the only ligand-gated Ca(2+)-permeable channels in the liver cell membrane identified so far. Several types of receptor-activated Ca(2+) channels have been identified, and some partially characterised. It is likely that TRP (transient receptor potential) polypeptides, which can form Ca(2+)- and Na(+)-permeable channels, comprise many hepatocyte receptor-activated Ca(2+)-permeable channels. A number of TRP proteins have been detected in hepatocytes and in liver cell lines. Further experiments are required to characterise the receptor-activated Ca(2+) permeable channels more fully, and to determine the molecular nature, mechanisms of activation, and precise physiological functions of each of the different hepatocyte plasma membrane Ca(2+) permeable channels.
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4
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Exton JH. Glucagon Signal‐Transduction Mechanisms. Compr Physiol 2001. [DOI: 10.1002/cphy.cp070213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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5
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Yamamoto NS, Merkle CJ, Kraus-Friedmann N. Disruption of filamentous actin diminishes hormonally evoked Ca2+ responses in rat liver. Metabolism 1999; 48:1241-7. [PMID: 10535385 DOI: 10.1016/s0026-0495(99)90262-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Previous studies have suggested a role for the actin cytoskeleton in hormonally evoked Ca2+ signaling in the liver. Here, we present evidence supporting a connection between filamentous actin (F-actin) organization and the ability of vasopressin and glucagon to increase cytosolic free-Ca2+ ([Ca2+]i) levels. F-actin was disrupted in hepatic cells by perfusion of rat liver with cytochalasin D. Epifluorescence microscopy of subsequently isolated cells showed reduced cortical fluorescent phalloidin staining in cytochalasin D-treated liver cells. Cytochalasin D pretreatment of liver cells reduced the vasopressin-stimulated elevation of [Ca2+]i by 60% and of glucagon by 50%. Experiments performed on cytochalasin D-treated cells using Mn2+ as an indicator of Ca2+ influx quenched fura-2 fluorescence signals following vasopressin administration. This indicates that a structurally intact cortical F-actin web is not a prerequisite for the influx of calcium. Therefore, the attenuation of the increase in cytosolic calcium observed in cytochalasin D-treated liver cells was likely caused either by the depletion of the calcium store by treatment with cytochalasin D or by the need for an intact cytoskeletal structure for its release. Because the resting level of calcium did not change in cells exposed to cytochalasin D, the latter is likely. The reduced [Ca2+]i response may be the mechanism by which cytochalasin D pretreatment inhibits vasopressin-induced metabolic effects. Cytochalasin D pretreatment also decreased the ability of glucagon to stimulate gluconeogenesis and reduced the stimulation of O2 uptake usually observed following glucagon administration. In conclusion, these results suggest that the hormonal elevation of [Ca2+]i and resultant activation of specific metabolic pathways require normal F-actin organization.
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Affiliation(s)
- N S Yamamoto
- Department of Integrative Biology, The University of Texas at Houston, 77225, USA
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Hansen LH, Gromada J, Bouchelouche P, Whitmore T, Jelinek L, Kindsvogel W, Nishimura E. Glucagon-mediated Ca2+ signaling in BHK cells expressing cloned human glucagon receptors. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:C1552-62. [PMID: 9611120 DOI: 10.1152/ajpcell.1998.274.6.c1552] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
From video imaging of fura 2-loaded baby hamster kidney (BHK) cells stably expressing the cloned human glucagon receptor, we found the Ca2+ response to glucagon to be specific, dose dependent, synchronous, sensitive to pertussis toxin, and independent of Ca2+ influx. Forskolin did not elicit a Ca2+ response, but treatment with a protein kinase A inhibitor, the Rp diastereomer of 8-bromoadenosine-3',5'-cyclic monophosphothioate, resulted in a reduced glucagon-mediated Ca2+ response as well as Ca2+ oscillations. The specific phospholipase C inhibitor U-73122 abolished the Ca2+ response to glucagon, and a modest twofold increase in inositol trisphosphate (IP3) production could be observed after stimulation with glucagon. In BHK cells coexpressing glucagon and muscarinic (M1) acetylcholine receptors, carbachol blocked the rise in intracellular free Ca2+ concentrations in response to glucagon, whereas glucagon did not affect the carbachol-induced increase in Ca2+. Furthermore, carbachol, but not glucagon, could block thapsigargin-activated increases in intracellular free Ca2+ concentration. These results indicate that, in BHK cells, glucagon receptors can activate not only adenylate cyclase but also a second independent G protein-coupled pathway that leads to the stimulation of phospholipase C and the release of Ca2+ from IP3-sensitive intracellular Ca2+ stores. Finally, we provide evidence to suggest that cAMP potentiates the IP3-mediated effects on intracellular Ca2+ handling.
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Affiliation(s)
- L H Hansen
- Department of Molecular Signaling, Hagedorn Research Institute, DK-2820 Gentofte, Denmark
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da Silva AC, Kelmer-Bracht AM, Constantin J, Ishii-Iwamoto EL, Yamamoto NS, Bracht A. The influence of Ca2+ on the effects of glucagon on hepatic glycolysis. GENERAL PHARMACOLOGY 1998; 30:655-62. [PMID: 9559315 DOI: 10.1016/s0306-3623(97)00381-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
1. The influence of Ca2+ on the effects of glucagon on glycolysis was investigated in the isolated perfused rat liver. Livers from fed rats were perfused in an open system with Krebs/Henseleit-bicarbonate buffer (pH 7.4). Glucose release, lactate plus pyruvate production (glycolysis) and oxygen uptake were measured. The following results were obtained: 2. In livers perfused with Ca(2+)-free Krebs/Henseleit-bicarbonate buffer and after depletion of the intracellular pools, the initial and transient stimulation of glycolysis, which is normally observed shortly after the onset of glucagon infusion, was more pronounced when compared to livers perfused with normal perfusion fluid (2.5 mM Ca2+) and without previous depletion of the intracellular pools (controls); the subsequent inhibition of glycolysis was delayed in Ca(2+)-free perfused livers and was less pronounced in comparison with the controls at the end of the glucagon infusion period (20 min). 3. Perfusion with a Ca(2+)-free medium supplemented with EDTA, without previous depletion of the intracellular pools, also produced a substantial reduction in the effects of glucagon on glycolysis. 4. Ca(2+)-free perfusion did not affect the stimulative action of glucagon on glucose release (glycogenolysis) and oxygen uptake. 5. Glycolysis inhibition by cAMP also was abolished in Ca(2+)-free perfused livers, and the initial stimulation was enhanced. 6. Mn2+, a metal ion known as a competitor of Ca2+, considerably reduced the action of glucagon on glycolysis; Mn2+ did not affect the basal rates of glycolysis. 7. Sr2+, a metal ion that is often recognized as Ca2+ by several biological structures and processes, increased the inhibitory action of glucagon on glycolysis. 8. Several organic compounds, which directly or indirectly take part in Ca2+ fluxes, were also able to diminish (e.g., verapamil) or even to abolish (carbenoxolone) the inhibitory action of glucagon on glycolysis. 9. It was concluded that, under the conditions of the living cell, Ca2+ is important for glycolysis inhibition by glucagon. In principle at least, the results can be explained in terms of the known Ca2+ dependencies of several protein kinases and protein phosphatases.
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Affiliation(s)
- A C da Silva
- Laboratory of Liver Metabolism, University of Maringá, Brazil
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8
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García MV, Hernández-Berciano R, López-Mediavilla C, Orfao A, Medina JM. cAMP and Ca2+ involvement in the mitochondrial response of cultured fetal rat hepatocytes to adrenaline. Exp Cell Res 1997; 237:403-9. [PMID: 9434636 DOI: 10.1006/excr.1997.3804] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The effect of adrenaline on the control of respiratory activity of mitochondria from fetal hepatocytes in primary culture was studied. In the absence of adrenaline, the respiratory control ratio (RCR) of mitochondria increased during the first 3 days of culture due to a decrease in the rate of state 4 respiration. The presence of adrenaline in the incubation medium further increased the mitochondrial RCR through a decrease in the rate of respiration in state 4 and to an increase in the respiration rate in state 3. The effect of adrenaline was mimicked by dibutyryl-cAMP, forskolin, and isobutyl methyl xanthine. All these compounds increased cAMP concentrations, suggesting that cAMP may be involved in the effect of adrenaline. The increase in intracellular free Ca2+ concentrations caused by phenylephrine, vasopressin, or thapsigargin was also accompanied by an increase in the RCR, suggesting that both phenomena are associated. Dibutyryl-cAMP also increased free Ca2+ concentrations, suggesting that the effects of cAMP may be mediated by free Ca2+ concentrations. Adrenaline, dibutyryl-cAMP, phenylephrine, vasopressin, and thapsigargin promoted adenine nucleotide accumulation in mitochondria; this may be an intermediate step in the activation of mitochondrial respiratory function. These results suggest that the stimulatory effect of adrenaline on mitochondrial maturation in cultured fetal rat hepatocytes may be exerted through a mechanism in which both cAMP and Ca2+ act as second messengers. It is concluded that the effect of adrenaline on mitochondrial maturation is exerted by both alpha- and beta-adrenergic mechanisms and is mediated by the increase in adenine nucleotide contents of mitochondria.
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Affiliation(s)
- M V García
- Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Universidad de Salamanca, Spain
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9
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Marques-da-Silva AC, D'Avila RB, Ferrari AG, Kelmer-Bracht AM, Constantin J, Yamamoto NS, Bracht A. Ca2+ dependence of gluconeogenesis stimulation by glucagon at different cytosolic NAD(+)-NADH redox potentials. Braz J Med Biol Res 1997; 30:827-36. [PMID: 9361705 DOI: 10.1590/s0100-879x1997000700002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The influence of Ca2+ on hepatic gluconeogenesis was measured in the isolated perfused rat liver at different cytosolic NAD(+)-NADH potentials. Lactate and pyruvate were the gluconeogenic substrates and the cytosolic NAD(+)-NADH potentials were changed by varying the lactate to pyruvate ratios from 0.01 to 100. The following results were obtained: a) gluconeogenesis from lactate plus pyruvate was not affected by Ca(2+)-free perfusion (no Ca2+ in the perfusion fluid combined with previous depletion of the intracellular pools); gluconeogenesis was also poorly dependent on the lactate to pyruvate ratios in the range of 0.1 to 100; only for a ratio equal to 0.01 was a significantly smaller gluconeogenic activity observed in comparison to the other ratios. b) In the presence of Ca2+, the increase in oxygen uptake caused by the infusion of lactate plus pyruvate at a ratio equal to 10 was the most pronounced one; in Ca(2+)-free perfusion the increase in oxygen uptake caused by lactate plus pyruvate infusion tended to be higher for all lactate to pyruvate ratios; the most pronounced difference was observed for lactate/pyruvate ratio equal to 1. c) In the presence of Ca2+ the effects of glucagon on gluconeogenesis showed a positive correlation with the lactate to pyruvate ratios; for a ratio equal to 0.01 no stimulation occurred, but in the 0.1 to 100 range stimulation increased progressively, producing a clear parabolic dependence between the effects of glucagon and the lactate to pyruvate ratio. d) In the absence of Ca2+ the relationship between the changes caused by glucagon in gluconeogenesis and the lactate to pyruvate ratio was substantially changed; the dependence curve was no longer parabolic but sigmoidal in shape with a plateau beginning at a lactate/pyruvate ratio equal to 1; there was inhibition at the lactate to pyruvate ratios of 0.01 and 0.1 and a constant stimulation starting with a ratio equal to 1; for the lactate to pyruvate ratios of 10 and 100, stimulation caused by glucagon was much smaller than that found when Ca2+ was present. e) The effects of glucagon on oxygen uptake in the presence of Ca2+ showed a parabolic relationship with the lactate to pyruvate ratios which was closely similar to that found in the case of gluconeogenesis; the only difference was that inhibition rather than stimulation of oxygen uptake was observed for a lactate to pyruvate ratio equal to 0.01; progressive stimulation was observed in the 0.1 to 100 range. f) In the absence of Ca2+ the effects of glucagon on oxygen uptake were different; the dependence curve was sigmoidal at the onset, with a well-defined maximum at a lactate to pyruvate ratio equal to 1; this maximum was followed by a steady decline at higher ratios; at the ratios of 0.01 and 0.1 inhibition took place; oxygen uptake stimulation caused by glucagon was generally lower in the absence of Ca2+ except when the lactate to pyruvate ratio was equal to 1. The results of the present study demonstrate that stimulation of gluconeogenesis by glucagon depends on Ca2+. However, Ca2+ is only effective in helping gluconeogenesis stimulation by glucagon at highly negative redox potentials of the cytosolic NAD(+)-NADH system. The triple interdependence of glucagon-Ca(2+)-NAD(+)-NADH redox potential reveals highly complex interrelations that can only be partially understood at the present stage of knowledge.
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Affiliation(s)
- J Christophe
- Department of Experimental Surgery Medical School, Université Libre de Bruxelles, Belgium
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Feng L, Subbaraya I, Yamamoto N, Baehr W, Kraus-Friedmann N. Expression of photoreceptor cyclic nucleotide-gated cation channel alpha subunit (CNGCalpha) in the liver and skeletal muscle. FEBS Lett 1996; 395:77-81. [PMID: 8849693 DOI: 10.1016/0014-5793(96)01011-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Glucagon and beta-adrenergic agents increase cAMP levels and stimulate Ca2+ influx in liver cells. There is no consensus as to the mechanism by which these hormones stimulate the influx of Ca2+. Using mouse retinal rod CNGCalpha cDNA probes, we cloned rat liver and skeletal muscle, and human hepatic CNGCalpha subunit sequences showing 97-100% identity with the human rod channel. In order to assess channel activity, the effect of cyclic nucleotides on free intracellular Ca2+ levels of isolated hepatocytes was measured. Dibutyryl-cAMP was more effective in increasing free Ca2+ levels than dibutyryl-cGMP. These data indicate that the CNGCalpha subunit is expressed in both the liver and skeletal muscle possibly mediating hormonal effects on ion fluxes.
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Affiliation(s)
- L Feng
- Department of Integrative Biology, University of Texas-Houston School of Medicine, USA
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12
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Abstract
A hypothesis for the hormonal regulation of gluconeogenesis, in which increases in cytosolic free-Ca2+ levels ([Ca2+]i) play a major role, is presented. This hypothesis is based on the observation that gluconeogenic hormones evoke a common pattern of Ca2+ redistribution, resulting in increases in [Ca2+]i. Current concepts of hormonally evoked Ca2+ fluxes are presented and discussed. It is suggested that the increase in [Ca2+]i is functionally linked to stimulation of gluconeogenesis. The stimulation of gluconeogenesis is accomplished in two ways: (1) by increasing the activities of the Krebs cycle and the electron-transfer chain, thereby supplying adenosine triphosphates (ATP) and reducing equivalents to the process; and (2) by stimulating the activities of key gluconeogenic enzymes, such as pyruvate carboxylase. The hypothesis presents a conceptual framework that ties together two interrelated manifestations of hormone action: signal transduction and metabolism.
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Affiliation(s)
- N Kraus-Friedmann
- Department of Integrative Biology, University of Texas Medical School at Houston, 77225-0708, USA
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Hernández ML, Martínez MJ, Ruiz JI, Ochoa B. Stimulation of microsomal cholesterol ester hydrolase by glucagon, cyclic AMP analogues, and vasopressin in isolated rat hepatocytes. Lipids 1996; 31:269-76. [PMID: 8900456 DOI: 10.1007/bf02529873] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Short-term activation of microsomal cholesterol ester hydrolase by glucagon, cAMP analogues, and vasopressin in isolated rat hepatocytes is described. Glucagon led to a dose- and time-dependent activation of cholesteryl oleate hydrolysis, but values returned to basal levels within 120 min. Exposure of isolated hepatocytes to 0.5 mM concentrations of dibutyryl-cAMP or 8-[4-chlorophenylthio]-cAMP, or 25 microM forskolin caused persistent activation of cholesterol ester hydrolase activity after a lag period of 30 min. The three agents resulted in early marked intracellular accumulation of cAMP that declined progressively, and moderate and sustained reductions in the diacylglycerol content. The actions of glucagon on hepatocytes were inhibited by pretreatment of cells with 10 nM [8-arginine] vasopressin. Vasopressin elicited a consistent and sustained increase in cholesterol ester hydrolase activity and diacylglycerol without affecting cAMP while reducing the effect of glucagon on cAMP. Furthermore, the effects of glucagon and vasopressin on the activation of cholesterol ester hydrolase were not additive despite the similarity of their stimulation of diacylglycerol formation. Blockade of vasopressin-mediated activation of cholesterol ester hydrolase and diacylglycerol content were induced by excess prazosin. These data suggest that stimulation of microsomal cholesterol ester hydrolase in isolated liver cells may involve at least two signal transduction systems.
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Affiliation(s)
- M L Hernández
- Department of Physiology, University of the Basque County Medical School, Bilbao, Spain
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14
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Monti JA, Carnovale CE, Scapini C, Favre C, Carrillo MC. Role of calcium fluxes in the action of glucagon on cytosolic glutathione S-transferase activity in rat liver slices. PHARMACOLOGY & TOXICOLOGY 1995; 77:316-9. [PMID: 8778742 DOI: 10.1111/j.1600-0773.1995.tb01033.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
In a previous study we demonstrated that the administration of 20 micrograms/kg b.wt. of glucagon to rats caused a significant diminution of hepatic cytosolic glutathione S-transferase (GST) activity. This inhibition was non-competitive and reversible. We suggested that the effect would be mediated by cytosolic effectors. The present work was performed to characterize the mechanism involved in this inhibition. Liver tissue slices (170 to 200 mg) were incubated during different periods of time (0, 5, 10, 15, 20 and 30 min.) with several concentrations of glucagon (10(-5) M, 10(-8) M and 10(-10) M), dibutiryl cyclic AMP (10(-4) M, 10(-6) M and 10(-9) M), divalent cation ionophore A23187 (10(-4) M, 10(-6) M and 10(-9) M) or vasopressin (10(-7) M, 5 x 10(-7) M and 10(-8) M). The incubation was done with or without calcium in the medium. In all cases the cytosolic GST activity were determined in liver slices. The percentage of inhibition of GST activity was directly related to the increase of concentration of the test substances. An inhibition between 40% to 45% after 10 min. of incubation with the highest concentrations was observed (except vasopressin which caused 10% of inhibition). 10(-10) M glucagon did not produce a decrease of GST activity. The inhibition disappeared in calcium-free incubated slices, but direct relationship between plasma-membrane calcium influx and inhibition of GST activity (r = 0.950, P < 0.001, n = 24) could be obtained. By using calmodulin antagonists, we conclude that the inhibition process of the enzyme was mediated by calmodulin. In summary, we propose that plasma-membrane calcium influx induced by high concentrations of glucagon activates calmodulin, which promotes a modification (actually a methylation, according to other authors) on GST, thereby causing a decrease in its activity.
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Affiliation(s)
- J A Monti
- Institute of Experimental Physiology, CONICET-UNR, Faculty of Biochemical and Pharmaceutical Sciences, University of Rosario, Argentina
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Christophe J. Glucagon receptors: from genetic structure and expression to effector coupling and biological responses. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1241:45-57. [PMID: 7742347 DOI: 10.1016/0304-4157(94)00015-6] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- J Christophe
- Department of Experimental Surgery, Medical School, Université Libre de Bruxelles, Belgium
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16
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Cheek TR, Murawsky MM, Stauderman KA. Histamine-induced Ca2+ entry precedes Ca2+ mobilization in bovine adrenal chromaffin cells. Biochem J 1994; 304 ( Pt 2):469-76. [PMID: 7998982 PMCID: PMC1137516 DOI: 10.1042/bj3040469] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The relationship between histamine-induced Ca2+ mobilization and Ca2+ entry in bovine adrenal chromaffin cells has been investigated. Stopped-flow fluorimetry of fura-2-loaded chromaffin cell populations revealed that 10 microM histamine promoted entry of Ca2+ or Mn2+ without measurable delay (< or = 20 ms), through a pathway that was insensitive to the dihydropyridine antagonist nifedipine. In the absence of extracellular Ca2+, or in the presence of 100 microM La3+, a blocker of receptor-mediated Ca2+ entry, 10 microM histamine triggered an elevation in intracellular calcium concentration ([Ca2+]i), but only after a delay of approx. 200 ms, which presumably represented the time required to mobilize intracellular Ca2+. These data suggested that histamine-induced bivalent-cation entry precedes extensive Ca2+ mobilization in chromaffin cells. In order to confirm that histamine can promote Ca2+ entry largely independently of mobilizing intracellular Ca2+, the ability of histamine to promote Ca2+ entry into cells whose intracellular Ca2+ store had been largely depleted was assessed. Fura-2-loaded chromaffin cells were treated with 10 microM ryanodine together with 40 mM caffeine, to deplete the hormone-sensitive Ca2+ store. This resulted in an approx. 95% inhibition of histamine-induced Ca2+ release. Under these conditions, histamine was still able to promote an entry of Ca2+ that was essentially indistinguishable from that promoted in control cells. In single cells, introduction of heparin (100 mg/ml), but not de-N-sulphated heparin (100 mg/ml), abolished the histamine-induced rise in [Ca2+]i. All these data suggest that histamine can induce G-protein- or inositol phosphate-dependent rapid (< or = 20 ms) Ca2+ entry without an extensive intracellular mobilization response in chromaffin cells, which points to activation of an entry mechanism distinct from the Ca(2+)-release-activated Ca2+ channel found in non-excitable cells.
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Affiliation(s)
- T R Cheek
- AFRC Laboratory of Molecular Signalling, Department of Zoology, Cambridge, U.K
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17
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Sparks JD, Sparks CE. Insulin regulation of triacylglycerol-rich lipoprotein synthesis and secretion. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1215:9-32. [PMID: 7948013 DOI: 10.1016/0005-2760(94)90088-4] [Citation(s) in RCA: 154] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
This review has considered a number of observations obtained from studies of insulin in perfused liver, hepatocytes, transformed liver cells and in vivo and each of the experimental systems offers advantages. The evaluation of insulin effects on component lipid synthesis suggests that overall, lipid synthesis is positively influenced by insulin. Short-term high levels of insulin through stimulation of intracellular degradation of freshly translated apo B and effects on synthesis limit the ability of hepatocytes to form and secrete TRL. The intracellular site of apo B degradation may involve membrane-bound apo B, cytoplasmic apo B and apo B which has entered the ER lumen. How insulin favors intracellular apo B degradation is not known. An area of recent investigation is in insulin-stimulated phosphorylation of intracellular substrates such as IRS-1 which activates insulin specific cellular signaling molecules [245]. Candidate molecules to study insulin action on apo B include IRS-1 and SH2-containing signaling molecules. Insulin dysregulation in carbohydrate metabolism occurs in non-insulin-dependent diabetes mellitus due to an imbalance between insulin sensitivity of tissue and pancreatic insulin secretion (reviewed in Refs. [307,308]). Insulin resistance in the liver results in the inability to suppress hepatic glucose production; in muscle, in impaired glucose uptake and oxidation and in adipose tissue, in the inability to suppress release of free FA. This lack of appropriate sensitivity towards insulin action leads to hyperglycemia which in turn stimulates compensatory insulin secretion by the pancreas leading to hyperinsulinemia. Ultimately, there may be failure of the pancreas to fully compensate, hyperglycemia worsens and diabetes develops. The etiology of insulin resistance is being intensively studied for the primary defect may be over secretion of insulin by the pancreas or tissue insulin resistance and both of these defects may be genetically predetermined. We suggest that, in addition to effects in carbohydrate metabolism, insulin resistance in liver results in the inability of first phase insulin to suppress hepatic TRL production which results in hypertriglyceridemia leading to high levels of plasma FA which accentuate insulin resistance in other target organs. As recently reviewed [17,254] the role of insulin as a stimulator of hepatic lipogenesis and TRL production has been long established. Several lines of evidence support that insulin is stimulatory to the production of hepatic TRL in vivo. First, population based studies support a positive relationship between plasma insulin and total TG and VLDL [253]. Second, there is a strong association between chronic hyperinsulinemia and VLDL overproduction [309].(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- J D Sparks
- Department of Pathology, University of Rochester, School of Medicine and Dentistry, NY 14642
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18
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Green AK, Cobbold PH, Dixon CJ. Elevated intracellular cyclic AMP exerts different modulatory effects on cytosolic free Ca2+ oscillations induced by ADP and ATP in single rat hepatocytes. Biochem J 1994; 302 ( Pt 3):949-55. [PMID: 7945225 PMCID: PMC1137322 DOI: 10.1042/bj3020949] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Single aequorin-injected hepatocytes respond to agonists acting via the phosphoinositide signalling pathway by the generation of oscillations in cytosolic free Ca2+ concentration ([Ca2+]free). The duration of [Ca2+]free transients is characteristic of the stimulating agonist. We have previously reported that ADP and ATP, which are believed to act through a single P(2y)-purinoceptor species, induce very different oscillatory [Ca2+]free responses in the majority of hepatocytes. We have interpreted these data as evidence for two separate Ca(2+)-mobilizing purinoceptors for these nucleotides. We show here that the elevation of intracellular cyclic AMP concentration, by the co-application of either dibutyryl cyclic AMP or 7 beta-desacetyl-7 beta-[gamma-(N-methylpiperazino)butyryl]- forskolin (L858051), exerts different modulatory effects on [Ca2+]free oscillations induced by ADP and ATP in single rat hepatocytes. Elevated intracellular cyclic AMP levels enhance the frequency and peak [Ca2+]free of transients induced by ADP. In contrast, the elevation of intracellular cyclic AMP levels in hepatocytes producing [Ca2+]free oscillations in response to ATP stimulates either an increase in the duration of transients or a sustained rise in [Ca2+]free. The data illustrate a further difference between the oscillatory [Ca2+]free responses of hepatocytes to ADP and ATP, thus further arguing against ADP and ATP acting via a single purinoceptor species.
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Affiliation(s)
- A K Green
- Department of Human Anatomy and Cell Biology, University of Liverpool, U.K
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19
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Gamberucci A, Innocenti B, Fulceri R, Bànhegyi G, Giunti R, Pozzan T, Benedetti A. Modulation of Ca2+ influx dependent on store depletion by intracellular adenine-guanine nucleotide levels. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)31557-0] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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20
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Ichas F, Jouaville LS, Sidash SS, Mazat JP, Holmuhamedov EL. Mitochondrial calcium spiking: a transduction mechanism based on calcium-induced permeability transition involved in cell calcium signalling. FEBS Lett 1994; 348:211-5. [PMID: 8034044 DOI: 10.1016/0014-5793(94)00615-6] [Citation(s) in RCA: 124] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We report reversible Ca(2+)-induced Ca2+ release from mitochondria, which takes the form of Ca2+ spikes. Mitochondrial Ca2+ spiking is an all-or-none process with a threshold dependence on both the frequency and the amplitude of the Ca2+ pulses used as stimuli. This spiking relies on the transient operation of the mitochondrial permeability transition pore, and is initiated--in a threshold-dependent manner--with inositol-triphosphate-mediated Ca2+ responses on permeabilized cells. Evidence that mitochondrial Ca(2+)-induced Ca2+ release contributes to inositol-triphosphate-mediated Ca2+ responses in intact cells is also reported.
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Affiliation(s)
- F Ichas
- Groupe d'Etude des Systèmes Biologiques Intégrés, D(BM)2, Universitè Bordeaux II, France
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21
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Lupu-Meiri M, Lipinsky D, Ozaki S, Watanabe Y, Oron Y. Independent external calcium entry and cellular calcium mobilization in Xenopus oocytes. Cell Calcium 1994; 16:20-8. [PMID: 7525072 DOI: 10.1016/s0143-4160(05)80004-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
We studied cellular calcium (Ca) mobilization and Ca entry from the medium following injection of various inositol phosphates (IPs) or activation of thyrotropin-releasing hormone receptors (TRH-Rs) in oocytes injected with TRH-R cRNA. We determined the order of potency of various IPs for evoking the rapid depolarizing current in Ca-free medium, which reflects the mobilization of cellular Ca. The most potent compound was inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), followed by inositol 1,2,4,5-tetrakisphosphate (Ins(1,2,4,5)-P4), which displayed 91% of the activity of Ins(1,4,5)P3, while inositol 1,3,4,6-tetrakisphosphate (Ins(1,3,4,6)P4) had only 29% effect. All other IPs used in the present study exhibited responses that were 40% or less than those elicited by Ins(1,4,5)P3. Cellular Ca mobilization was confirmed by 45Ca2+ efflux for Ins(1,4,5)P3, Ins(1,2,4,5)P4 and Ins(1,3,4,6)P4, or by Fura-2 ratio imaging studies for the latter. In parallel, we assayed the ability of these compounds to promote Ca entry into the cell, as reflected by Ca-evoked depolarizing current or Fura-2 imaging. These assays revealed a different order of potency, where Ins(1,4,5)P3 > inositol 4,5-bisphosphate (Ins(4,5)P2) > Ins(1,3,4,6)P4 = Ins(1,2,4,5)P4. All other inositol phosphates were largely ineffective. Heparin inhibited the response to TRH by 67% while Ca entry was inhibited only by 22%. The latency of the response to TRH was significantly shorter in the presence of extracellular Ca, suggesting Ca entry preceded the response, i.e. major depletion of Ca stores. These results strongly suggest that the activation of Ca entry is largely independent of cellular Ca mobilization and may be mediated by a receptor for an unidentified phosphorylated compound, different from that for Ins(1,4,5)P3 on the endoplasmic reticulum.
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Affiliation(s)
- M Lupu-Meiri
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Israel
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22
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Kass GE, Gahm A, Llopis J. Cyclic AMP stimulates Ca2+ entry in rat hepatocytes by interacting with the plasma membrane carriers involved in receptor-mediated Ca2+ influx. Cell Signal 1994; 6:493-501. [PMID: 7818985 DOI: 10.1016/0898-6568(94)90003-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The regulation of Ca2+ influx in rat hepatocytes by glucagon and cyclic AMP (cAMP) was investigated. Exposing hepatocytes to glucagon resulted in an increase in the initial rate of Ca2+ entry. The concentrations of glucagon producing half-maximal and maximal stimulation of Ca2+ entry were 10(-10) and 10(-8) M, respectively. A similar stimulation of Ca2+ influx was obtained in cells exposed to cAMP analogues or to forskolin. Exposing hepatocytes suspended in nominally Ca(2+)-free medium to glucagon for 3 min produced a 9% decrease in the size of the vasopressin-sensitive Ca2+ pool; in contrast, N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (Bt2cAMP) slightly augmented the size of this pool. Glucagon and Bt2cAMP synergized the initial vasopressin-stimulated Ca2+ and Mn2+ influx rates, but only moderately increased the initial rate of Ca2+ entry after thapsigargin addition. The glucagon- and Bt2cAMP-stimulated Ca2+ influx was inhibited by the same antagonists of the plasma membrane Ca2+ carriers that mediate Ca2+ entry during stimulation by vasopressin. Thus, cAMP does not stimulate Ca2+ entry through either a capacitative type of mechanism or inositol phosphate turnover. The authors' findings instead suggest that cAMP acts directly, or through protein kinase A on the same Ca2+ carriers that are activated by phospholipase C-linked receptor agonists.
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Affiliation(s)
- G E Kass
- Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden
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23
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Björnsson OG, Sparks JD, Sparks CE, Gibbons GF. Regulation of VLDL secretion in primary culture of rat hepatocytes: involvement of cAMP and cAMP-dependent protein kinases. Eur J Clin Invest 1994; 24:137-48. [PMID: 8206083 DOI: 10.1111/j.1365-2362.1994.tb00979.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
When hepatocytes were cultured for 24 h in the presence of forskolin (10(-4) mol l-1) or isobutylmethylxanthine (IBMX, 10(-3) mol l-1), the intracellular cAMP concentration peaked (320-380 pmol mg-1 protein) after 10-20 min of culture. This increase was accompanied by a decrease in the secretion of triacylglycerol, cholesterol and apoprotein B associated with VLDL. After 4 h cAMP levels had returned almost to basal values but the inhibition of VLDL secretion persisted. There was a small intracellular accumulation of triacylglycerol but not of apoprotein B. Addition of forskolin and IBMX together led to a further increase in intracellular cAMP and a further suppression of VLDL output. Similar effects on the secretion of VLDL were also observed after addition of Bt2cAMP. Exposure of cell cultures to glucagon (10(-7) mol l-1) for only 10 min raised cellular cAMP levels to > 200 pmol mg-1 protein, and suppressed VLDL secretion during the next 24 h to < 40% of control. All of the substances tested inhibited de novo synthesis of fatty acids but had little or no effect on cholesterol synthesis and did not inhibit oleate esterification to triacylglycerol. The cAMP-dependent protein kinase antagonist Rp-cAMPS prevented suppression of VLDL triacylglycerol secretion induced by glucagon (10(-7) mol l-1) and abolished glucagon-induced ketogenesis. Rp-cAMPS also inhibited Bt2cAMP (7.5 x 10(-6) mol l-1)-induced suppression of VLDL secretion and enhancement of ketogenesis. It is concluded that rat hepatic VLDL metabolism can be regulated by cAMP and cAMP-dependent protein kinases, and that the initial transient rise in cellular cAMP levels induced by glucagon is sufficient to maintain a long-term inhibitory effect on assembly and secretion of VLDL.
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Affiliation(s)
- O G Björnsson
- Metabolic Research Laboratory, Radcliffe Infirmary, Oxford, UK
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24
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Bygrave FL, Karjalainen A, Hamada Y. Crosstalk between calcium- and cyclic AMP-mediated signalling systems and the short-term modulation of bile flow in normal and cholestatic rat liver. Cell Signal 1994; 6:1-9. [PMID: 8011424 DOI: 10.1016/0898-6568(94)90055-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The flow of bile is subject to short-term modulation by glucagon and calcium-mobilizing hormones. Of potential relevance is the crosstalk between the second messenger-mediated signal transducing systems of these agonists. This latter point has revealed an area of investigation that should enable further insights to be made into a physiological network that interrelates bile flow, hepatocellular calcium movements and hormone action. This information in turn may provide insights into the etiology and treatment of human and animal diseases in which cholestasis is an underlying feature.
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Affiliation(s)
- F L Bygrave
- Division of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra
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25
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Bygrave FL, Benedetti A. Calcium: its modulation in liver by cross-talk between the actions of glucagon and calcium-mobilizing agonists. Biochem J 1993; 296 ( Pt 1):1-14. [PMID: 8250828 PMCID: PMC1137647 DOI: 10.1042/bj2960001] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- F L Bygrave
- Division of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra, ACT
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