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Li W, Kirchner T, Ho G, Bonilla F, D'Aquino K, Littrell J, Zhang R, Jian W, Qiu X, Zheng S, Gao B, Wong P, Leonard JN, Camacho RC. Amino acids are sensitive glucagon receptor-specific biomarkers for glucagon-like peptide-1 receptor/glucagon receptor dual agonists. Diabetes Obes Metab 2020; 22:2437-2450. [PMID: 33463043 DOI: 10.1111/dom.14173] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Revised: 08/10/2020] [Accepted: 08/12/2020] [Indexed: 12/31/2022]
Abstract
AIM The aim of this study was to evaluate amino acids as glucagon receptor (GCGR)-specific biomarkers in rodents and cynomolgus monkeys in the presence of agonism of both glucagon-like peptide-1 receptor (GLP1R) and GCGR with a variety of dual agonist compounds. MATERIALS AND METHODS Primary hepatocytes, rodents (normal, diet-induced obese and GLP1R knockout) and cynomolgus monkeys were treated with insulin (hepatocytes only), glucagon (hepatocytes and cynomolgus monkeys), the GLP1R agonist, dulaglutide, or a variety of dual agonists with varying GCGR potencies. RESULTS A long-acting dual agonist, Compound 2, significantly decreased amino acids in both wild-type and GLP1R knockout mice in the absence of changes in food intake, body weight, glucose or insulin, and increased expression of hepatic amino acid transporters. Dulaglutide, or a variant of Compound 2 lacking GCGR agonism, had no effect on amino acids. A third variant with ~31-fold less GCGR potency than Compound 2 significantly decreased amino acids, albeit to a significantly lesser extent than Compound 2. Dulaglutide (with saline infusion) had no effect on amino acids, but an infusion of glucagon dose-dependently decreased amino acids on the background of GLP1R engagement (dulaglutide) in cynomolgus monkeys, as did Compound 2. CONCLUSIONS These results show that amino acids are sensitive and translatable GCGR-specific biomarkers.
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Affiliation(s)
- Wenyu Li
- Cardiovascular Metabolism Discovery, Janssen R&D, Spring House, Pennsylvania, USA
| | - Thomas Kirchner
- Cardiovascular Metabolism Discovery, Janssen R&D, Spring House, Pennsylvania, USA
| | - George Ho
- Cardiovascular Metabolism Discovery, Janssen R&D, Spring House, Pennsylvania, USA
| | - Fany Bonilla
- Cardiovascular Metabolism Discovery, Janssen R&D, Spring House, Pennsylvania, USA
| | - Katharine D'Aquino
- Cardiovascular Metabolism Discovery, Janssen R&D, Spring House, Pennsylvania, USA
| | - James Littrell
- Cardiovascular Metabolism Discovery, Janssen R&D, Spring House, Pennsylvania, USA
| | - Rui Zhang
- Cardiovascular Metabolism Discovery, Janssen R&D, Spring House, Pennsylvania, USA
| | - Wenying Jian
- Pharmacokinetics, Dynamics, and Metabolism, Janssen R&D, Spring House, Pennsylvania, USA
| | - Xi Qiu
- Pharmacokinetics, Dynamics, and Metabolism, Janssen R&D, Spring House, Pennsylvania, USA
| | - Songmao Zheng
- Janssen Biotherapeutics, Janssen R&D, Spring House, Pennsylvania, USA
| | - Bin Gao
- Translational Medicine and Early Development Statistics, Janssen R&D, Spring House, Pennsylvania, USA
| | - Peggy Wong
- Quantitative Sciences, Janssen R&D, Raritan, New Jersey, USA
| | - James N Leonard
- Cardiovascular Metabolism Discovery, Janssen R&D, Spring House, Pennsylvania, USA
| | - Raul C Camacho
- Cardiovascular Metabolism Discovery, Janssen R&D, Spring House, Pennsylvania, USA
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2
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Galsgaard KD, Jepsen SL, Kjeldsen SAS, Pedersen J, Wewer Albrechtsen NJ, Holst JJ. Alanine, arginine, cysteine, and proline, but not glutamine, are substrates for, and acute mediators of, the liver-α-cell axis in female mice. Am J Physiol Endocrinol Metab 2020; 318:E920-E929. [PMID: 32255678 DOI: 10.1152/ajpendo.00459.2019] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The aim of this study was to identify the amino acids that stimulate glucagon secretion in mice and whose metabolism depends on glucagon receptor signaling. Pancreata of female C57BL/6JRj mice were perfused with 19 individual amino acids and pyruvate (at 10 mM), and secretion of glucagon was assessed using a specific glucagon radioimmunoassay. Separately, a glucagon receptor antagonist (GRA; 25-2648, 100 mg/kg) or vehicle was administered to female C57BL/6JRj mice 3 h before an intraperitoneal injection of four different isomolar amino acid mixtures (in total 7 µmol/g body wt) as follows: mixture 1 contained alanine, arginine, cysteine, and proline; mixture 2 contained aspartate, glutamate, histidine, and lysine; mixture 3 contained citrulline, methionine, serine, and threonine; and mixture 4 contained glutamine, leucine, isoleucine, and valine. Blood glucose, plasma glucagon, amino acid, and insulin concentrations were measured using well-characterized methodologies. Alanine (P = 0.03), arginine (P < 0.0001), cysteine (P = 0.01), glycine (P = 0.02), lysine (P = 0.02), and proline (P = 0.03), but not glutamine (P = 0.9), stimulated glucagon secretion from the perfused mouse pancreas. However, when the four isomolar amino acid mixtures were administered in vivo, the four mixtures elicited similar glucagon responses (P > 0.5). Plasma concentrations of total amino acids in vivo were higher after administration of GRA when mixture 1 (P = 0.004) or mixture 3 (P = 0.04) were injected. Our data suggest that alanine, arginine, cysteine, and proline, but not glutamine, are involved in the acute regulation of the liver-α-cell axis in female mice, as they all increased glucagon secretion and their disappearance rate was altered by GRA.
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Affiliation(s)
- Katrine D Galsgaard
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Sara L Jepsen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Sasha A S Kjeldsen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jens Pedersen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- Department of Nephrology and Endocrinology, Nordsjaellands Hospital Hilleroed, University of Copenhagen, Hilleroed, Denmark
| | - Nicolai J Wewer Albrechtsen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- Department of Clinical Biochemistry, Rigshospitalet, Copenhagen, Denmark
- Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jens J Holst
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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3
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Galsgaard KD, Pedersen J, Kjeldsen SAS, Winther-Sørensen M, Stojanovska E, Vilstrup H, Ørskov C, Wewer Albrechtsen NJ, Holst JJ. Glucagon receptor signaling is not required for N-carbamoyl glutamate- and l-citrulline-induced ureagenesis in mice. Am J Physiol Gastrointest Liver Physiol 2020; 318:G912-G927. [PMID: 32174131 DOI: 10.1152/ajpgi.00294.2019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Glucagon regulates the hepatic amino acid metabolism and increases ureagenesis. Ureagenesis is activated by N-acetylglutamate (NAG), formed via activation of N-acetylglutamate synthase (NAGS). With the aim to identify the steps whereby glucagon both acutely and chronically regulates ureagenesis, we investigated whether glucagon receptor-mediated activation of ureagenesis is required in a situation where NAGS activity and/or NAG levels are sufficient to activate the first step of the urea cycle in vivo. Female C57BL/6JRj mice treated with a glucagon receptor antagonist (GRA), glucagon receptor knockout (Gcgr-/-) mice, and wild-type (Gcgr+/+) littermates received an intraperitoneal injection of N-carbamoyl glutamate (Car; a stable variant of NAG), l-citrulline (Cit), Car and Cit (Car + Cit), or PBS. In separate experiments, Gcgr-/- and Gcgr+/+ mice were administered N-carbamoyl glutamate and l-citrulline (wCar + wCit) in the drinking water for 8 wk. Car, Cit, and Car + Cit significantly (P < 0.05) increased plasma urea concentrations, independently of pharmacological and genetic disruption of glucagon receptor signaling (P = 0.9). Car increased blood glucose concentrations equally in GRA- and vehicle-treated mice (P = 0.9), whereas the increase upon Car + Cit was impaired in GRA-treated mice (P = 0.008). Blood glucose concentrations remained unchanged in Gcgr-/- mice upon Car (P = 0.2) and Car + Cit (P = 0.9). Eight weeks administration of wCar + wCit did not change blood glucose (P > 0.2), plasma amino acid (P > 0.4), and urea concentrations (P > 0.3) or the area of glucagon-positive cells (P > 0.3) in Gcgr-/- and Gcgr+/+ mice. Our data suggest that glucagon-mediated activation of ureagenesis is not required when NAGS activity and/or NAG levels are sufficient to activate the first step of the urea cycle.NEW & NOTEWORTHY Hepatic ureagenesis is essential in amino acid metabolism and is importantly regulated by glucagon, but the exact mechanism is unclear. With the aim to identify the steps whereby glucagon both acutely and chronically regulates ureagenesis, we here show, contrary to our hypothesis, that glucagon receptor-mediated activation of ureagenesis is not required when N-acetylglutamate synthase activity and/or N-acetylglutamate levels are sufficient to activate the first step of the urea cycle in vivo.
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Affiliation(s)
- Katrine D Galsgaard
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jens Pedersen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Department of Endocrinology and Nephrology, Nordsjaellands Hospital Hilleroed, Hilleroed, Denmark
| | - Sasha A S Kjeldsen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Marie Winther-Sørensen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Elena Stojanovska
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Hendrik Vilstrup
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
| | - Cathrine Ørskov
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Nicolai J Wewer Albrechtsen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Department of Clinical Biochemistry, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark.,Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jens J Holst
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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4
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Hamdi MM, Mutungi G. Dihydrotestosterone stimulates amino acid uptake and the expression of LAT2 in mouse skeletal muscle fibres through an ERK1/2-dependent mechanism. J Physiol 2011; 589:3623-40. [PMID: 21606113 DOI: 10.1113/jphysiol.2011.207175] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Dihydrotestosterone (DHT) has acute/non-genomic actions in adult mammalian skeletal muscles whose physiological functions are still poorly understood. Therefore, the primary aim of this study was to investigate the acute/non-genomic effects of DHT on amino acid uptake as well as the cellular signal transduction events underlying these actions in mouse fast- and slow-twitch skeletal muscle fibre bundles. 14C-Labelled amino acids were used to investigate the effects of DHT and testosterone (T) on amino acid uptake and pharmacological interventions were used to determine the cellular signal transduction events mediating these actions. While T had no effect on the uptake of isoleucine (Ile) and α-methylaminoisobutyric acid (MeAIB) in both fibre types, DHT increased their uptake in the fast-twitch fibre bundles. This effect was reversed by inhibitors of protein translation, the epidermal growth factor receptor (EGFR), system A, system L, mTOR and MEK. However, it was relatively insensitive to inhibitors of transcription, androgen receptors and PI3K/Akt. Additionally, DHT treatment increased the expression of LAT2 and the phosphorylation of the EGFR in the fast-twitch fibre bundles and that of ERK1/2, RSK1/2 and ATF2 in both fibre types. Also, it decreased the phosphorylation of eEF2 and increased the incorporation of Ile into proteins in both fibre types. Most of these effects were reversed by EGFR and MEK inhibitors. From these findings we suggest that another physiological function of the acute/non-genomic actions of DHT in isolated mammalian skeletal muscle fibres is to stimulate amino acid uptake. This effect is mediated through the EGFR and involves the activation of the MAPK pathway and an increase in LAT2 expression.
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Affiliation(s)
- M M Hamdi
- Biomedical and Clinical Sciences Research Institute, School of Medicine, Health Policy and Practice, University of East Anglia, Norwich NR4 7TJ, UK
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5
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6
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Gómez T, Medina V, Ramírez CM, Dópido R, Lorenzo A, Díaz M. Regulation of L-alanine transport systems A and ASC by cyclic AMP and calcium in a reptilian duodenal model. J Exp Biol 2003; 206:1589-98. [PMID: 12654897 DOI: 10.1242/jeb.00280] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The regulation of neutral amino acid transport by cyclic AMP (cAMP) and calcium across the isolated duodenum of the lizard Gallotia galloti has been studied under short-circuit conditions. Active L-alanine transport was stimulated by forskolin, theophylline and dibutyryl cyclic AMP (db-cAMP). All these agents increased transmural potential difference (PD) and short-circuit current (I(sc)) in a manner consistent with the activation of a chloride secretory pathway. Both forskolin and theophylline increased intracellular cAMP levels in the lizard duodenal mucosa. Addition of calcium ionophore A23187 rapidly reduced mucosa-to-serosa L-alanine fluxes and diminished net L-alanine transport. Despite the reduction of alanine fluxes by A23187, transepithelial PD and I(sc) values were increased by the ionophore. Analyses of the responses of isolated transport pathways indicated that the Na(+)-independent L-alanine transport system was unaffected by db-cAMP or calcium ionophore. By contrast, Na(+)-dependent transport activities were profoundly modified by these agents. Thus, while system A [alpha-methylamino-isobutiric acid (MeAIB)-transporting pathway] was stimulated by increased calcium, system ASC activity was nearly abolished. Calcium ionophore also potentiated the electrogenic response of system A. Forskolin strongly stimulated system ASC activity but left system A activity unchanged. Activation of system ASC by forskolin was clearly electroneutral, as pre-incubation of the tissues with the chloride channel blocker diphenylamine-2-carboxilic acid (DPC) completely prevented forskolin-induced transepithelial electrical responses. It is concluded that intracellular messengers cAMP and calcium oppositely modulate active Na(+)-dependent (L)-alanine transport in the lizard intestine. The different sensitivity exhibited by individual transport pathways may well account for the changes observed in overall alanine transport.
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Affiliation(s)
- Tomás Gómez
- Laboratorio de Fisiología Animal, Departamento de Biología Animal, Universidad de La Laguna, 38206 Tenerife, Spain
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7
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Abstract
The effects of vasoactive intestinal polypeptide (VIP) and of forskolin on alanine metabolism in hepatocytes isolated from fed and fasted rats were examined. VIP and 17 microM forskolin stimulated glucose production, gluconeogenesis from alanine, and ureagenesis, and inhibited glyconeogenesis to comparable degrees. However, combination of 17 microM forskolin with a maximal dose of VIP significantly augmented only the inhibition of glyconeogenesis. At 100 microM, forskolin induced metabolic responses comparable to those induced by glucagon, but similarly, in combination with maximal doses of VIP or glucagon, augmented only inhibition of glycogen synthesis. In addition to demonstrating modulation of alanine metabolism by VIP and forskolin, these results raise questions about the nature of the coupling between VIP receptor occupancy and metabolic response.
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8
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García F, Kierbel A, Larocca MC, Gradilone SA, Splinter P, LaRusso NF, Marinelli RA. The water channel aquaporin-8 is mainly intracellular in rat hepatocytes, and its plasma membrane insertion is stimulated by cyclic AMP. J Biol Chem 2001; 276:12147-52. [PMID: 11278499 DOI: 10.1074/jbc.m009403200] [Citation(s) in RCA: 162] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
We previously found that water transport across hepatocyte plasma membranes occurs mainly via a non-channel mediated pathway. Recently, it has been reported that mRNA for the water channel, aquaporin-8 (AQP8), is present in hepatocytes. To further explore this issue, we studied protein expression, subcellular localization, and regulation of AQP8 in rat hepatocytes. By subcellular fractionation and immunoblot analysis, we detected an N-glycosylated band of approximately 34 kDa corresponding to AQP8 in hepatocyte plasma and intracellular microsomal membranes. Confocal immunofluorescence microscopy for AQP8 in cultured hepatocytes showed a predominant intracellular vesicular localization. Dibutyryl cAMP (Bt(2)cAMP) stimulated the redistribution of AQP8 to plasma membranes. Bt(2)cAMP also significantly increased hepatocyte membrane water permeability, an effect that was prevented by the water channel blocker dimethyl sulfoxide. The microtubule blocker colchicine but not its inactive analog lumicolchicine inhibited the Bt(2)cAMP effect on both AQP8 redistribution to cell surface and hepatocyte membrane water permeability. Our data suggest that in rat hepatocytes AQP8 is localized largely in intracellular vesicles and can be redistributed to plasma membranes via a microtubule-depending, cAMP-stimulated mechanism. These studies also suggest that aquaporins contribute to water transport in cAMP-stimulated hepatocytes, a process that could be relevant to regulated hepatocyte bile secretion.
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Affiliation(s)
- F García
- Instituto de Fisiologia Experimental, Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET), Universidad Nacional de Rosario, Rosario, Santa Fe, Argentina 2000
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9
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Battezzati A, Simonson DC, Luzi L, Matthews DE. Glucagon increases glutamine uptake without affecting glutamine release in humans. Metabolism 1998; 47:713-23. [PMID: 9627372 DOI: 10.1016/s0026-0495(98)90036-1] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Glucagon causes transient hyperglycemia and persistent hypoaminoacidemia, but the mechanisms of this action are unclear. To address this question, the present study measured the effects of glucagon on glucose, leucine, phenylalanine, and glutamine kinetics. Seven healthy subjects each underwent three pancreatic clamp studies (octreotide 30 ng/kg/min, insulin 0.15 mU/kg/min, and glucagon 1.4 ng/kg/min) lasting 7 hours. During the last 3.5 hours of the studies, glucagon infusion was either unchanged (study 0) or increased to 4 and 7 ng/kg/min (studies 1 and 2). The higher glucagon infusion rates increased the glucagon concentration by 50% and 100%, respectively. [6,6-(2)H2]glucose, [2-(15)N]glutamine, 2H5-phenylalanine, and 2H3-leucine were infused to quantify the respective fluxes. Glucagon transiently increased glucose concentrations by stimulating glucose production, which peaked in 15 minutes to 3.82 +/- 0.36 and 4.21 +/- 0.33 mg/kg/min in studies 1 and 2 and then returned to the postabsorptive levels. Glucagon decreased the glutamine concentration (-10% +/- 2% and -22% +/- 2% in studies 1 and 2 v study 0, P < .05), because glutamine uptake became greater than glutamine release (balance from -1.9 +/- 0.9 in study 0 to -8.1 +/- 1.1 and -13.6 +/- 1.0 micromol/kg/h in studies 1 and 2, P < .01). Glucagon decreased the leucine concentration (-11% +/- 3% in study 2 v study 0, P < .02) and caused a small increment in proteolysis (+6% in study 2 v study 0, P < .01) that was related to the decrement in glutamine concentrations. Phenylalanine kinetics were not significantly affected. These results show that glucagon promotes the uptake of gluconeogenic substrates but does not increase their release, suggesting that glucagon-induced hyperglycemia is short-lived because glucagon fails to provide more fuel for gluconeogenesis. The small increase in proteolysis and the depletion of circulating glutamine prove that physiologic hyperglucagonemia can contribute to protein catabolism.
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Affiliation(s)
- A Battezzati
- Department of Medicine, Brigham and Women's Hospital, Boston, MA, USA
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10
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Mukhopadhayay S, Ananthanarayanan M, Stieger B, Meier PJ, Suchy FJ, Anwer MS. cAMP increases liver Na+-taurocholate cotransport by translocating transporter to plasma membranes. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:G842-8. [PMID: 9357825 DOI: 10.1152/ajpgi.1997.273.4.g842] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Adenosine 3',5'-cyclic monophosphate (cAMP), acting via protein kinase A, increases transport maximum of Na+-taurocholate cotransport within 15 min in hepatocytes (S. Grüne, L. R. Engelking, and M. S. Anwer. J. Biol. Chem. 268: 17734-17741, 1993); the mechanism of this short-term stimulation was investigated. Cycloheximide inhibited neither basal nor cAMP-induced increases in taurocholate uptake in rat hepatocytes, indicating that cAMP does not stimulate transporter synthesis. Studies in plasma membrane vesicles showed that taurocholate uptake was not stimulated by the catalytic subunit of protein kinase A but was higher when hepatocytes were pretreated with cAMP. Immunoblot studies with anti-fusion protein antibodies to the cloned Na+-taurocholate cotransport polypeptide (Ntcp) showed that pretreatment of hepatocytes with cAMP increased Ntcp content in plasma membranes but not in homogenates. Ntcp was detected in microsomes, endosomes, and Golgi fractions, and cAMP pretreatment resulted in a decrease only in endosomal Ntcp content. It is proposed that cAMP increases transport maximum of Na+-taurocholate cotransport, at least in part, by translocating Ntcp from endosomes to plasma membranes.
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Affiliation(s)
- S Mukhopadhayay
- Department of Medicine, Tufts University School of Veterinary Medicine, North Grafton, Massachusetts 01536, USA
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11
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Lim SK, De Bandt JP, Aussel C, Pernet P, Giboudeau J, Cynober L. No evidence for a tumor necrosis factor alpha stimulated 2-methylaminoisobutyric acid uptake in hepatocyte monolayer. J Cell Physiol 1995; 162:422-6. [PMID: 7860649 DOI: 10.1002/jcp.1041620314] [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: 01/27/2023]
Abstract
This study investigates the short-term effects of glucagon and human recombinant tumor necrosis factor alpha (TNF alpha) singly and in association on 2-methylaminoisobutyric acid (MeAIB) transport in hepatocyte monolayers. As expected, glucagon induced a time-dependent stimulation of MeAIB transport. In our experimental conditions, TNF alpha did not induce cytolysis. A 2 hour exposure to TNF alpha (0.05-500 ng/l) with or without glucagon (10(-9) to 10(-6) M) did not modify the basal or glucagon-stimulated MeAIB transport. Varying the duration of exposure to TNF alpha 5 ng/l up to 6 h was equally ineffective. The presence of hydrocortisone potentiated the glucagon-stimulated transport, but TNF alpha remained ineffective. Finally, the association of interferon (IFN gamma) with TNF alpha and/or glucagon was unable to modify the transport activity. These data demonstrate that TNF alpha does not exert a direct effect on MeAIB transport in hepatocytes, at least on a short-term basis.
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Affiliation(s)
- S K Lim
- Laboratoire de Biochimie A, Hôpital Saint-Antoine, Paris, France
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12
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McGivan JD, Pastor-Anglada M. Regulatory and molecular aspects of mammalian amino acid transport. Biochem J 1994; 299 ( Pt 2):321-34. [PMID: 8172590 PMCID: PMC1138275 DOI: 10.1042/bj2990321] [Citation(s) in RCA: 264] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- J D McGivan
- Department of Biochemistry, School of Medical Sciences, Bristol, U.K
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13
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Komori T, Hotta N, Kobayashi M, Sakakibara F, Koh N, Sakamoto N. Biguanides may produce hypoglycemic action in isolated rat hepatocytes through their effects on L-alanine transport. Diabetes Res Clin Pract 1993; 22:11-7. [PMID: 8137711 DOI: 10.1016/0168-8227(93)90127-q] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
We investigated the mechanisms of the effects of the biguanides metformin and buformin on hepatic gluconeogenesis in hepatocytes isolated from normal rats. Both 10 nM glucagon and 50 microM dibutyryl cAMP increased [3H]alanine uptake in isolated hepatocytes of normal rats by about 150% and 55%, respectively, compared with the effect of 5 mM alanine alone. Metformin (3 mM) reduced glucagon-stimulated [3H]alanine uptake to the level seen with alanine alone; buformin (3 mM) inhibited glucagon-stimulated [3H]alanine uptake by about 69%. The effects of biguanides on dibutyryl cAMP-stimulated [3H]alanine uptake were similar, but of smaller magnitude compared with those observed in the presence of glucagon. Ouabain (3 mM) had a stronger inhibitory effect on [3H]alanine uptake than the biguanides. However, 3 mM tolbutamide failed to suppress [3H]alanine uptake in the presence or absence of glucagon or dibutyryl cAMP. Our results suggest that the inhibition of alanine uptake, related to a reduction in the Na+/L-alanine transport system, is a possible mechanism of biguanide-related inhibition of hepatic gluconeogenesis.
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Affiliation(s)
- T Komori
- Third Department of Internal Medicine, Nagoya University School of Medicine, Japan
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14
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Low SY, Taylor PM, Hundal HS, Pogson CI, Rennie MJ. Transport of L-glutamine and L-glutamate across sinusoidal membranes of rat liver. Effects of starvation, diabetes and corticosteroid treatment. Biochem J 1992; 284 ( Pt 2):333-40. [PMID: 1350902 PMCID: PMC1132642 DOI: 10.1042/bj2840333] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
There is increasing evidence that membrane transporters for glutamine and glutamate are involved in control of liver metabolism in health and disease. We therefore investigated the effects of three catabolic states [starvation (60 h), diabetes (4 days after streptozotocin treatment) and corticosteroid (8-day dexamethasone) treatment] associated with altered hepatic amino acid metabolism on the activity of glutamine and glutamate transporters in sinusoidal membrane vesicles from livers of treated rats. In control preparations, L-[14C]glutamine uptake was largely Na(+)-dependent, but L-[14C]glutamate uptake was largely Na(+)-independent. Vmax. values for Na(+)-dependent uptake of glutamine and/or glutamate exceeded control values (by about 2- and 12-fold respectively) in liver membrane vesicles from starved (glutamine), diabetic (glutamate) or steroid-treated (glutamine and glutamate) rats. The Km values for Na(+)-dependent transport of glutamine or glutamate and the rates of their Na(+)-independent uptake were not significantly altered by any treatment. Na(+)-independent glutamate uptake appeared to include a dicarboxylate-exchange component. The patterns of inhibition of glutamine and glutamate uptake by other amino acids indicated that the apparent induction of Na(+)-dependent amino acid transport in catabolic states included increased functional expression of systems A, N (both for glutamine) and X-ag (for glutamate). The results demonstrate that conditions resulting in increased secretion of catabolic hormones (e.g. corticosteroid, glucagon) are associated with increased capacity for Na(+)-dependent transport of amino acids into liver cells from the blood. The modulation of hepatic permeability to glutamine and glutamate in these situations may control the availability of amino acids for intrahepatic metabolic processes such as ureagenesis, ammonia detoxification and gluconeogenesis.
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Affiliation(s)
- S Y Low
- Department of Anatomy and Physiology, University of Dundee, U.K
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Cheeseman CI. Molecular mechanisms involved in the regulation of amino acid transport. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1991; 55:71-84. [PMID: 1871316 DOI: 10.1016/0079-6107(91)90001-9] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- C I Cheeseman
- Department of Physiology, University of Alberta, Edmonton, Canada
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Moule SK, McGivan JD. Regulation of the plasma membrane potential in hepatocytes--mechanism and physiological significance. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1031:383-97. [PMID: 1977473 DOI: 10.1016/0304-4157(90)90016-6] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- S K Moule
- Department of Biochemistry, School of Medical Sciences, University of Bristol, U.K
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Expression of rat liver Na+/L-alanine co-transport in Xenopus laevis oocytes. Effect of glucagon in vivo. Biochem J 1990; 270:189-95. [PMID: 2396979 PMCID: PMC1131697 DOI: 10.1042/bj2700189] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Poly(A)+ RNA (mRNA) isolated from rat liver was injected into Xenopus laevis oocytes, and expression of Na+/L-alanine transport was assayed by measuring Na(+)-dependent uptake of L-[3H]alanine. Expression of Na+/L-alanine transport was detected 3-7 days after mRNA injection, and was due to an increment of the Na(+)-dependent component. After injection of 40 ng of total mRNA, Na(+)-dependent uptake of L-alanine was 2.5-fold higher than in water-injected oocytes. In contrast with Na+/L-alanine transport by water-injected oocytes, expressed Na+/L-alanine transport was inhibited by N-methylaminoisobutyric acid, was inhibited by an extracellular pH of 6.5 and was saturated at approx. 1 mM-L-alanine. After sucrose-density-gradient fractionation, highest expression of Na+/L-alanine uptake was observed with mRNA of 1.9-2.5 kb in length. Compared with mRNA isolated from control rats, mRNA isolated from glucagon-treated rats showed a approx. 2-fold higher expression of Na+/L-alanine transport. The results demonstrate that both liver Na+/L-alanine transport systems (A and ASC) can be expressed in X. laevis oocytes. Furthermore, the data obtained with mRNA isolated from glucagon-treated rats suggest that glucagon regulates liver Na+/L-alanine transport (at least in part) via the availability of the corresponding mRNA.
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Moule SK, McGivan JD. Epidermal growth factor and cyclic AMP stimulate Na+/H+ exchange in isolated rat hepatocytes. EUROPEAN JOURNAL OF BIOCHEMISTRY 1990; 187:677-82. [PMID: 2154379 DOI: 10.1111/j.1432-1033.1990.tb15353.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Na+/H+ exchange in acid-loaded isolated hepatocytes was measured using the intracellular pH indicator biscarboxyethyl-carboxyfluorescein (BCECF) to follow intracellular pH (pHi). The rate of amiloride-sensitive Na(+)-dependent recovery from cytoplasmic-acid-loading was found to be increased in cells treated with epidermal growth factor (EGF), 8-(4-chlorophenylthio)adenosine 3',5'-monophosphate (ClPhScAMP) or phorbol 12-myristate 13-acetate (PMA). These three agents increased the rate of Na+/H+ exchange to similar extents and their effects were not additive. The stimulation was shown in all three cases to be due an alkaline shift of 0.1 in the set point pH of the Na+/H+ exchanger. Experiments measuring the uptake of 22Na+ into acid-loaded primary hepatocyte monolayer cultures confirmed these results. EGF, ClPhScAMP and PMA significantly increased the amiloride-inhibitable accumulation of 22Na+, thus providing further evidence that Na+/H+ exchange is stimulated by these effectors.
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Affiliation(s)
- S K Moule
- Department of Biochemistry, School of Medical Sciences, Bristol, England
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Moule SK, McGivan JD. Epidermal growth factor, like glucagon, exerts a short-term stimulation of alanine transport in rat hepatocytes. Biochem J 1987; 247:233-5. [PMID: 3500715 PMCID: PMC1148393 DOI: 10.1042/bj2470233] [Citation(s) in RCA: 35] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Epidermal growth factor causes a transient stimulation of alanine transport in hepatocytes. The stimulation is maximal after 30 min, and the rate returns to the control value after 90 min. These characteristics are very similar to the short-term stimulation of alanine transport by glucagon, which has been attributed to cell membrane hyperpolarization.
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Affiliation(s)
- S K Moule
- Department of Biochemistry, University of Bristol Medical School, U.K
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Gebhardt R, Kleemann E. Hormonal regulation of amino acid transport system N in primary cultures of rat hepatocytes. EUROPEAN JOURNAL OF BIOCHEMISTRY 1987; 166:339-44. [PMID: 3301340 DOI: 10.1111/j.1432-1033.1987.tb13520.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The transport of histidine and glutamine via system N in cultured hepatocytes was found to be subject to hormonal control. This long-term regulation showed the following characteristics. The transport capacity for histidine and glutamine (system N) increased slowly in response to the combination of dexamethasone and insulin to about 4-fold that of controls after 18-30 h. A similar time course was found for the stimulation of system N (2.5-fold) by dexamethasone and glucagon. In contrast the uptake of alpha-aminoisobutyric acid (system A) was rapidly stimulated 3-fold by dexamethasone and insulin and 5-fold by dexamethasone and glucagon within 3-6 h but decreased towards control rates after 24 h of cultivation in minimal essential medium. Dexamethasone, insulin and glucagon each stimulated glutamine uptake about 2-fold in cultures maintained in W/AB 77 medium, while the combination of dexamethasone with either glucagon or insulin resulted in a 3-4-fold increase. Dexamethasone was most effective at about 0.1 microM. Higher concentrations were less efficient. Insulin reached its optimal effect at concentrations above 1 microM. Kinetic analysis revealed that the increased capacity of glutamine transport in response to hormones was due to an increase in Vmax, while Km was essentially unchanged. The hormone-induced stimulation of system N was prevented by cycloheximide. The induced uptake of glutamine was inhibited by excess amounts of asparagine and histidine but not of alpha-methylaminoisobutyric acid or cysteine. These results clearly differentiate the hormonal regulation of system N from that of system A.
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Moule SK, Bradford NM, McGivan JD. Short-term stimulation of Na+-dependent amino acid transport by dibutyryl cyclic AMP in hepatocytes. Characteristics and partial mechanism. Biochem J 1987; 241:737-43. [PMID: 3036071 PMCID: PMC1147625 DOI: 10.1042/bj2410737] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The short-term protein-synthesis-independent stimulation of alanine transport in hepatocytes was further investigated. Cyclic AMP increased the Vmax. of alanine transport. Amino acid transport via systems A, ASC and N was stimulated. A good correlation was found between the initial rate of transport and the cell membrane potential as calculated from the distribution of Cl-. Cyclic AMP increased the rate of alanine transport, stimulated Na+/K+ ATPase (Na+/K+-transporting ATPase) activity and caused membrane hyperpolarization. The time courses and cyclic AMP dose-dependencies of all three effects were similar. Ouabain abolished the effect of cyclic AMP on Cl- distribution and on transport of alanine. The effect of cyclic AMP on alanine transport and Cl- distribution was mimicked by the antibiotic nigericin; the effect of nigericin was also abolished by ouabain. It is concluded that the effect of cyclic AMP on transport is mediated via membrane hyperpolarization. It is suggested that the primary action of cyclic AMP is to increase the activity of an electroneutral Na+/K+-exchange system in the liver cell plasma membrane, thus hyperpolarizing the membrane by stimulating the electrogenic Na+/K+ ATPase.
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The use of 36Cl- to measure cell plasma membrane potential in isolated hepatocytes--effects of cyclic AMP and bicarbonate ions. BIOCHIMICA ET BIOPHYSICA ACTA 1985; 845:10-6. [PMID: 2983771 DOI: 10.1016/0167-4889(85)90047-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The plasma membrane potential of hepatocytes was calculated from the distribution of 36Cl-. The potential observed under several conditions was equivalent to that previously measured using microelectrodes in perfused liver. Dibutyryl cAMP increased the membrane potential. Replacement of bicarbonate ions by morpholinosulphonate decreased the potential and reduced the effect of cAMP. The effect of both bicarbonate and cAMP was abolished by ouabain. Both bicarbonate and cAMP stimulated the activity of the (Na+ + K+)-ATPase as measured by ouabain-inhibitable 86Rb+ uptake. It is suggested that the stimulation of alanine transport by these effectors is mediated by an increase in cell membrane potential via stimulation of the (Na+ + K+)-ATPase.
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Rabkin M, Blum JJ. Quantitative analysis of intermediary metabolism in hepatocytes incubated in the presence and absence of glucagon with a substrate mixture containing glucose, ribose, fructose, alanine and acetate. Biochem J 1985; 225:761-86. [PMID: 3919712 PMCID: PMC1144654 DOI: 10.1042/bj2250761] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Hepatocytes were isolated from the livers of fed rats and incubated, in the presence and absence of 100 nM-glucagon, with a substrate mixture containing glucose (10 mM), fructose (4 mM), alanine (3.5 mM), acetate (1.25 mM), and ribose (1 mM). In any given incubation one substrate was labelled with 14C. Incorporation of 14C into glucose, glycogen, CO2, lactate, alanine, glutamate, lipid glycerol and fatty acids was measured after 20 and 40 min of incubation under quasi-steady-state conditions [Borowitz, Stein & Blum (1977) J. Biol. Chem. 252, 1589-1605]. These data and the measured O2 consumption were analysed with the aid of a structural metabolic model incorporating all reactions of the glycolytic, gluconeogenic, and pentose phosphate pathways, and associated mitochondrial and cytosolic reactions. A considerable excess of experimental measurements over independent flux parameters and a number of independent measurements of changes in metabolite concentrations allowed for a stringent test of the model. A satisfactory fit to the data was obtained for each condition. Significant findings included: control cells were glycogenic and glucagon-treated cells glycogenolytic during the second interval; an ordered (last in, first out) model of glycogen degradation [Devos & Hers (1979) Eur. J. Biochem. 99, 161-167] was required in order to fit the experimental data; the pentose shunt contributed approx. 15% of the carbon for gluconeogenesis in both control and glucagon-treated cells; net flux through the lower Embden-Meyerhof pathway was in the glycolytic direction except during the 20-40 min interval in glucagon-treated cells; the increased gluconeogenesis in response to glucagon was correlated with a decreased pyruvate kinase flux and lactate output; fluxes through pyruvate kinase, pyruvate carboxylase, and phosphoenolpyruvate carboxykinase were not coordinately controlled; Krebs cycle activity did not change with glucagon treatment; flux through the malic enzyme was towards pyruvate formation except for control cells during interval II; and 'futile' cycling at each of the five substrate cycles examined (including a previously undescribed cycle at acetate/acetyl-CoA) consumed about 26% of cellular ATP production in control hepatocytes and 21% in glucagon-treated cells.
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Kilberg MS, Barber EF, Handlogten ME. Characteristics and hormonal regulation of amino acid transport system A in isolated rat hepatocytes. CURRENT TOPICS IN CELLULAR REGULATION 1985; 25:133-63. [PMID: 2410197 DOI: 10.1016/b978-0-12-152825-6.50009-6] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Lerner J. Effectors of amino acid transport processes in animal cell membranes. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. A, COMPARATIVE PHYSIOLOGY 1985; 81:713-39. [PMID: 2863064 DOI: 10.1016/0300-9629(85)90903-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Various effectors, which act upon ion gradients, protein synthesis, membrane components or cellular functional groups, have been employed to provide insights into the nature of amino acid-membrane transport processes in animal cells. Such effectors, for example, include ions, hormones, metabolites and various organic reagents and their judicious use has allowed the following list of conclusions. Sodium ion has been found to stimulate amino acid transport in a wide variety of cell systems, although depending on the tissue and/or substrate, this ion may have no effect on such transport, or even inhibit it. Amino acid transport can be stimulated in some cell systems by other ions such as K+, Li+, H+ or Cl-. Both H+ and K+ have been found to be inhibitory in other systems. Amino acid transport is dependent in many cell systems upon an inwardly directed Na+ gradient and is stimulated by a membrane potential (negative cell interior). In some cell systems an inwardly directed Cl- and H+ gradient or an outwardly directed K+ gradient can energize transport. Structurally dissimilar effectors such as ouabain, Clostridium enterotoxin, aspirin and amiloride inhibit amino acid transport presumably through dissipation of the Na+ gradient. Inhibition by certain sugars or metabolic intermediates of the tricarboxylic acid cycle may compete with the substrate for the energy of the Na+ gradient or interact with the substrate at the carrier level either allosterically or at a common site. Stimulation of transport by other sugars or intermediates may result from their catabolism to furnish energy for transport. Insulin and glucagon stimulate transport of amino acids in a variety of cell systems by a mechanism which involves protein synthesis. Microtubules may be involved in the regulation of transport by insulin or glucagon. Some reports also suggest that insulin has a direct effect on membranes. In addition, a number of growth hormones and factors have stimulatory effects on amino acid transport which are also mediated by protein synthesis. Steroid hormones have been noted to enhance or diminish transport of amino acids depending on the nature of the hormone. These agents appear to function at the level of protein synthesis. While stimulation may involve increased carrier synthesis, inhibition probably involves synthesis of a labile protein which either decreases the rate of synthesis or increases the rate of degradation of a component of the transport system.(ABSTRACT TRUNCATED AT 400 WORDS)
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Hayes MR, McGivan JD. Comparison of the effects of certain thiol reagents on alanine transport in plasma membrane vesicles from rat liver and their use in identifying the alanine carrier. Biochem J 1983; 214:489-95. [PMID: 6615478 PMCID: PMC1152271 DOI: 10.1042/bj2140489] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The Na+-dependent uptake of alanine into plasma membrane vesicles from rat liver was inhibited by N-ethylmaleimide (NEM) and by mersalyl. NEM did not inhibit alanine-independent Na+ uptake and the inhibition of alanine transport by NEM was protected by pre-incubation with an excess of substrate. It was therefore concluded that NEM acted by binding to the alanine carrier. A protein of Mr 20 000 was found to bind NEM with a concentration dependence parallel to the NEM inhibition of alanine transport. The inhibition of binding of [3H]NEM to this protein by mersalyl had a concentration dependence similar to that of the inhibition of transport by mersalyl. Preincubation with L-alanine, but not with D-alanine, led to protection of the Mr 20 000 protein from binding NEM. It is concluded that this protein is an essential component of the alanine transport system.
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Shotwell MA, Kilberg MS, Oxender DL. The regulation of neutral amino acid transport in mammalian cells. BIOCHIMICA ET BIOPHYSICA ACTA 1983; 737:267-84. [PMID: 6303424 DOI: 10.1016/0304-4157(83)90003-5] [Citation(s) in RCA: 378] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Kilberg MS, Vida TA, Barber EF. Regulation of neutral amino acid transport in hepatocytes isolated from adrenalectomized rats. J Cell Physiol 1983; 114:45-52. [PMID: 6338022 DOI: 10.1002/jcp.1041140108] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The present report shows that System A-mediated 2-aminoisobutyric acid (AIB) uptake is elevated in hepatocytes isolated from adrenalectomized rats when they are compared to control cells. Although System ASC activity also shows this perturbation, Systems N, beta, L1, and L2 are unaffected. Transport of AIB in both cell types is stimulated by dexamethasone, insulin, and glucagon, yet the hepatocytes from the adrenalectomized rats are much less responsive to these hormones. This apparent decrease in competence is seen for adaptive regulation of System A as well. The in vitro addition of dexamethasone to the hepatocytes from the adrenalectomized animals does not restore fully their ability to respond to hormones or amino acid deprivation. These effects are observed even after the cells have been held in primary culture for 24 hr. The simultaneous addition of glucagon and dexamethasone to either cell type resulted in stimulation of transport to rates significantly greater than the sum of the increases produced by the two hormones when added separately. In contrast, insulin and dexamethasone were additive in their effects rather than synergistic. These results suggest that hepatocytes from adrenalectomized rats are less competent than control cells with respect to regulation of neutral amino acid transport, including stimulation by insulin or amino acid starvation, two processes which appear not to depend on glucocorticoid for maximal response.
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Barber EF, Handlogten ME, Vida TA, Kilberg MS. Neutral amino acid transport in hepatocytes isolated from streptozotocin-induced diabetic rats. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)33377-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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Mohri T, Sasaki H. Stimulatory effect of glucagon and dibutyryl-cAMP specifically on the Na+-independent amino acid transport of Chang liver cell. Biochem Biophys Res Commun 1982; 108:854-60. [PMID: 6293505 DOI: 10.1016/0006-291x(82)90909-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Fafournoux P, Rémésy C, Demigné C. Stimulation of amino acid transport into liver cells from rats adapted to a high-protein diet. Biochem J 1982; 206:13-8. [PMID: 7126187 PMCID: PMC1158543 DOI: 10.1042/bj2060013] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
After adaptation of rats to a 90%-casein diet, hepatic uptake of alanine is strikingly increased in vivo, with concomitant appearance of a concentration of favourable for uptake. With a high-protein diet, uptake of 2-aminoisobutyrate by isolated hepatocytes in the presence of various concentrations of substrates suggested induction of the A system (high-affinity system), whose emergence has been reported during starvation or after glucagon treatment. The other system (ASC, L) were characterized: induction processes only affected the A system. Dibutyryl cyclic AMP addition resulted in an increase in 2-aminoisobutyrate transport at low substrate concentration, the response being greater after adaptation to a high-protein diet. Evidence is presented suggesting that the increased uptake of amino acids by the liver of rats fed on high-protein diets is obtained by developing favourable gradients and enhancing transport capacities. These adaptations allow sufficient amounts of amino acids to enter the liver, where accelerated metabolism plays a decisive role.
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Bourdel G, Forestier M. Circadian variations of A-mediated transport in rat-liver plasma membrane vesicles. FEBS Lett 1982; 143:81-5. [PMID: 6288453 DOI: 10.1016/0014-5793(82)80278-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Abstract
Improvements in the collagenase perfusion techniques have made isolated rat hepatocytes a popular model in which to study hepatic function. Our knowledge of hepatic amino acid transport has been advanced as a result of this methodology. Translocation across the hepatocyte plasma membrane can, in some instances, represent the rate-limiting step in the overall metabolism of certain amino acids. Furthermore, regulation of amino acid uptake by hepatocytes appears to play a role in diabetes, and perhaps in malignant transformation. Comparisons between normal adult hepatocytes and several hepatoma cell lines show basic differences in amino acid transport. There are at least eight distinct systems in normal hepatocytes for transport of the hormones. Systems A and N exhibit enhanced uptake rates after the cells have been maintained in the absence of extracellular amino acids, a phenomenon termed adaptive control. Further studies using isolated hepatocytes will increase our basic understanding of membrane transport processes and their regulation.
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McGivan JD, Ramsell JC, Lacey JH. Stimulation of alanine transport and metabolism by dibutyryl cyclic AMP in the hepatocytes from fed rats. Assessment of transport as a potential rate-limiting step for alanine metabolism. BIOCHIMICA ET BIOPHYSICA ACTA 1981; 644:295-304. [PMID: 6266469 DOI: 10.1016/0005-2736(81)90387-4] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
(1) Cyclic AMP stimulated alanine transport in isolated hepatocytes by approx. 30%, in the range 0.2-5 mM alanine. (2) Alanine utilisation was also stimulated by cyclic AMP. The rates of transport and metabolism were comparable, both in the presence and absence of cyclic AMP. (3) At concentrations of alanine above 1 mM, addition of ouabain, or the reduction of the Na+ concentration, could partially inhibit transport without affecting the rate of metabolism. (4) At these alanine concentrations, stimulation of metabolism by cyclic AMP was associated with a decrease in the intracellular to extracellular alanine concentration ratio. (5) At alanine concentrations below 0.5 mM, or at higher concentrations when transport was inhibited by reducing the Na+ concentration, cyclic AMP caused an increase in the alanine concentration ratio. (6) It is concluded that at concentrations of alanine above 1 mM, alanine transport is not rate-limiting for alanine metabolism in hepatocytes from fed rats, and cyclic AMP stimulates alanine metabolism primarily by an effect on an intracellular reaction. At physiological concentrations of alanine, however, alanine transport appears to be rate-limiting in agreement with a previous report.
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Mak WW, Pitot HC. Microfilament accumulation and the transport of amino acids and glucose in adult rat hepatocytes cultured on collagen gel/nylon mesh. Biochem Biophys Res Commun 1981; 98:203-10. [PMID: 7213384 DOI: 10.1016/0006-291x(81)91889-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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38
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