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Mikkelsen ACD, Thomsen KL, Vilstrup H, Aamann L, Jones H, Mookerjee RP, Hamilton-Dutoit S, Frystyk J, Aagaard NK. Potassium deficiency decreases the capacity for urea synthesis and markedly increases ammonia in rats. Am J Physiol Gastrointest Liver Physiol 2021; 320:G474-G483. [PMID: 33404376 DOI: 10.1152/ajpgi.00136.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Accepted: 12/07/2020] [Indexed: 01/31/2023]
Abstract
Our study provides novel findings of experimental hypokalemia reducing urea cycle functionality and thereby severely increasing plasma ammonia. This is pathophysiologically interesting because plasma ammonia increases during hypokalemia by a hitherto unknown mechanism, which may be particular important in relation to the unexplained link between hypokalemia and hepatic encephalopathy. Potassium deficiency decreases gene expression, protein synthesis, and growth. The urea cycle maintains body nitrogen homeostasis including removal of toxic ammonia. Hyperammonemia is an obligatory trait of liver failure, increasing the risk for hepatic encephalopathy, and hypokalemia is reported to increase ammonia. We aimed to clarify the effects of experimental hypokalemia on the in vivo capacity of the urea cycle, on the genes of the enzymes involved, and on ammonia concentrations. Female Wistar rats were fed a potassium-free diet for 13 days. Half of the rats were then potassium repleted. Both groups were compared with pair- and free-fed controls. The following were measured: in vivo capacity of urea-nitrogen synthesis (CUNS); gene expression (mRNA) of urea cycle enzymes; plasma potassium, sodium, and ammonia; intracellular potassium, sodium, and magnesium in liver, kidney, and muscle tissues; and liver sodium/potassium pumps. Liver histology was assessed. The diet induced hypokalemia of 1.9 ± 0.4 mmol/L. Compared with pair-fed controls, the in vivo CUNS was reduced by 34% (P < 0.01), gene expression of argininosuccinate synthetase 1 (ASS1) was decreased by 33% (P < 0.05), and plasma ammonia concentrations were eightfold elevated (P < 0.001). Kidney and muscle tissue potassium contents were markedly decreased but unchanged in liver tissue. Protein expressions of liver sodium/potassium pumps were unchanged. Repletion of potassium reverted all the changes. Hypokalemia decreased the capacity for urea synthesis via gene effects. The intervention led to marked hyperammonemia, quantitatively explainable by the compromised urea cycle. Our findings motivate clinical studies of patients with liver disease.
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Affiliation(s)
| | - Karen Louise Thomsen
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
- UCL Institute of Liver and Digestive Health, University College London, London, United Kingdom
| | - Hendrik Vilstrup
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
| | - Luise Aamann
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
| | - Helen Jones
- UCL Institute of Liver and Digestive Health, University College London, London, United Kingdom
| | - Rajeshwar P Mookerjee
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
- UCL Institute of Liver and Digestive Health, University College London, London, United Kingdom
| | | | - Jan Frystyk
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Niels Kristian Aagaard
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
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Cochrane DR, Jacobsen BM, Connaghan KD, Howe EN, Bain DL, Richer JK. Progestin regulated miRNAs that mediate progesterone receptor action in breast cancer. Mol Cell Endocrinol 2012; 355:15-24. [PMID: 22330642 PMCID: PMC4716679 DOI: 10.1016/j.mce.2011.12.020] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/13/2011] [Revised: 11/23/2011] [Accepted: 12/29/2011] [Indexed: 01/01/2023]
Abstract
Progesterone receptors (PRs) mediate response to progestins in the normal breast and breast cancer. To determine if liganded PR regulate microRNAs (miRNAs) as a component of their action, we profiled mature miRNA levels following progestin treatment. Indeed, 28 miRNAs are significantly altered by 6h of progestin treatment. Many progestin-responsive genes are putative targets of progestin-regulated miRNAs; for example, progestin treatment decreases miR-29, thereby relieving repression of one of its direct targets, the gene encoding ATPase, Na(+)/K(+) transporting, beta 1 polypeptide (ATP1B1). Thus, liganded PR regulates ATP1B1 through sites in the promoter and the 3'UTR, to achieve maximal tight hormonal regulation of ATP1B1 protein via both transcriptional and translational control. We find that ATP1B1 serves to limit migration and invasion in breast cancer cells. Lastly, we demonstrate that PR itself is regulated by a progestin-upregulated miRNA, miR-513a-5p, providing a novel mechanism for tight control of PR protein expression.
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Affiliation(s)
- Dawn R. Cochrane
- Department of Pathology, University of Colorado Denver Anschutz Medical Campus, Denver, USA
| | - Britta M. Jacobsen
- Department of Medicine, University of Colorado Denver Anschutz Medical Campus, Denver, USA
| | - Keith D. Connaghan
- Department of Pharmaceutical Sciences, University of Colorado Denver Anschutz Medical Campus, Denver, USA
| | - Erin N. Howe
- Department of Pathology, University of Colorado Denver Anschutz Medical Campus, Denver, USA
| | - David L. Bain
- Department of Pharmaceutical Sciences, University of Colorado Denver Anschutz Medical Campus, Denver, USA
| | - Jennifer K. Richer
- Department of Pathology, University of Colorado Denver Anschutz Medical Campus, Denver, USA
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Connaghan KD, Heneghan AF, Miura MT, Bain DL. Na(+) and K(+) allosterically regulate cooperative DNA binding by the human progesterone receptor. Biochemistry 2010; 49:422-31. [PMID: 20000807 DOI: 10.1021/bi901525m] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Cooperativity is a common mechanism used by transcription factors to generate highly responsive yet stable gene regulation. For the two isoforms of human progesterone receptor (PR-A and PR-B), differences in cooperative DNA binding energetics may account for their differing transcriptional activation properties. Here we report on the molecular origins responsible for cooperativity, finding that it can be activated or repressed with Na(+) and K(+), respectively. We demonstrate that PR self-association and DNA-dependent cooperativity are linked to a monovalent cation binding event and that this binding is coupled to modulation of receptor structure. K(+) and Na(+) are therefore allosteric effectors of PR function. Noting that the apparent binding affinities of Na(+) and K(+) are comparable to their intracellular concentrations and that PR isoforms directly regulate the genes of a number of ion pumps and channels, these results suggest that Na(+) and K(+) may additionally function as physiological regulators of PR action.
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Affiliation(s)
- Keith D Connaghan
- Department of Pharmaceutical Sciences, University of Colorado Denver, Aurora, Colorado 80045, USA
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Yin W, Yin FZ, Shen WX, Cai BC, Hua ZC. Requirement of hydrogen peroxide and Sp1 in the stimulation of Na,K-ATPase by low potassium in MDCK epithelial cells. Int J Biochem Cell Biol 2008; 40:942-53. [DOI: 10.1016/j.biocel.2007.10.036] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2007] [Revised: 10/17/2007] [Accepted: 10/28/2007] [Indexed: 01/07/2023]
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Wang G, Kawakami K, Gick G. Divergent signaling pathways mediate induction of Na,K-ATPase α1 and β1 subunit gene transcription by low potassium. Mol Cell Biochem 2006; 294:73-85. [PMID: 16909306 DOI: 10.1007/s11010-006-9247-y] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2005] [Accepted: 05/16/2006] [Indexed: 11/25/2022]
Abstract
Prolonged inhibition of Na,K-ATPase enzymatic activity by exposure of a variety of mammalian cells to low external K+ yields a subsequent adaptive up-regulation of Na,K-ATPase expression. The aim of this study was to examine the intracellular signal transduction system that is responsible for mediating increased Na,K-ATPase subunit gene expression in primary cultures of neonatal rat cardiac myocytes. In this work, we show long-term inhibition of Na,K-ATPase function with 0.6 mM K+ resulted in hypertrophy of cardiac myocytes and augmentation of Na,K-ATPase alpha1 and beta1 subunit gene expression. Transient transfection experiments in neonatal rat cardiac myocytes demonstrated that low K+ induction of alpha1 and beta1 gene transcription was dependent on intracellular Ca2+ and activation of calcineurin. Based on effects of pharmacological inhibitors, protein kinase A (PKA), extracellular signal-regulated kinase 1/2 (ERK1/2) and histone deacetylase were found to be unique downstream components in the low K+ signal transduction pathway leading to increased alpha1 subunit promoter activity. Similarly, low K+-induced beta1 subunit gene transcription was dependent on activation of protein kinase C (PKC), c-Jun-N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK). These findings indicate that persistent inhibition of Na,K-ATPase activity with low external K+ activates overlapping and Na,K-ATPase subunit gene-specific signaling pathways in cardiac myocytes.
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Affiliation(s)
- Gang Wang
- Department of Biochemistry and Center for Cardiovascular and Muscle Research, State University of New York Health Science Center at Brooklyn, NY 11203, USA
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6
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Murphy KT, Macdonald WA, McKenna MJ, Clausen T. Ionic mechanisms of excitation-induced regulation of Na+-K+-ATPase mRNA expression in isolated rat EDL muscle. Am J Physiol Regul Integr Comp Physiol 2006; 290:R1397-406. [PMID: 16357096 DOI: 10.1152/ajpregu.00707.2005] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study investigated the effects of electrical stimulation on Na+-K+-ATPase isoform mRNA, with the aim to identify factors modulating Na+-K+-ATPase mRNA in isolated rat extensor digitorum longus (EDL) muscle. Interventions designed to mimic exercise-induced increases in intracellular Na+and Ca2+contents and membrane depolarization were examined. Muscles were mounted on force transducers and stimulated with 60-Hz 10-s pulse trains producing tetanic contractions three times at 10-min intervals. Ouabain (1.0 mM, 120 min), veratridine (0.1 mM, 30 min), and monensin (0.1 mM, 30 min) were used to increase intracellular Na+content. High extracellular K+(13 mM, 60 min) and the Ca2+ionophore A-23187 (0.02 mM, 30 min) were used to induce membrane depolarization and elevated intracellular Ca2+content, respectively. Muscles were analyzed for Na+-K+-ATPase α1–α3and β1–β3mRNA (real-time RT-PCR). Electrical stimulation had no immediate effect on Na+-K+-ATPase mRNA; however at 3 h after stimulation, it increased α1, α2, and α3mRNA by 223, 621, and 892%, respectively ( P = 0.010), without changing β mRNA. Ouabain, veratridine, and monensin increased intracellular Na+content by 769, 724, and 598%, respectively ( P = 0.001) but did not increase mRNA of any isoform. High intracellular K+concentration elevated α1mRNA by 160% ( P = 0.021), whereas A-23187 elevated α3mRNA by 123% ( P = 0.035) but reduced β1mRNA by 76% ( P = 0.001). In conclusion, electrical stimulation induced subunit-specific increases in Na+-K+-ATPase mRNA in isolated rat EDL muscle. Furthermore, Na+-K+-ATPase mRNA appears to be regulated by different stimuli, including cellular changes associated with membrane depolarization and increased intracellular Ca2+content but not increased intracellular Na+content.
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Affiliation(s)
- K T Murphy
- School of Human Movement, Recreation and Performance, Centre for Ageing, Rehabilitation and Sport Science, Victoria University of Technology, Melbourne, Australia.
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Murphy KT, Petersen AC, Goodman C, Gong X, Leppik JA, Garnham AP, Cameron-Smith D, Snow RJ, McKenna MJ. Prolonged submaximal exercise induces isoform-specific Na+-K+-ATPase mRNA and protein responses in human skeletal muscle. Am J Physiol Regul Integr Comp Physiol 2006; 290:R414-24. [PMID: 16179492 DOI: 10.1152/ajpregu.00172.2005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study investigated effects of prolonged submaximal exercise on Na+-K+-ATPase mRNA and protein expression, maximal activity, and content in human skeletal muscle. We also investigated the effects on mRNA expression of the transcription initiator gene, RNA polymerase II (RNAP II), and key genes involved in protein translation, eukaryotic initiation factor-4E (eIF-4E) and 4E-binding protein 1 (4E-BP1). Eleven subjects (6 men, 5 women) cycled at 75.5% (SD 4.8%) peak O2uptake and continued until fatigue. A vastus lateralis muscle biopsy was taken at rest, fatigue, and 3 and 24 h postexercise. We analyzed muscle for Na+-K+-ATPase α1, α2, α3, β1, β2, and β3, as well for RNAP II, eIF-4E, and 4E-BP1 mRNA expression by real-time RT-PCR and Na+-K+-ATPase isoform protein abundance using immunoblotting. Muscle homogenate maximal Na+-K+-ATPase activity was determined by 3 -O-methylfluorescein phosphatase activity and Na+-K+-ATPase content by [3H]ouabain binding. Cycling to fatigue [54.5 (SD 20.6) min] immediately increased α3( P = 0.044) and β2mRNA ( P = 0.042) by 2.2- and 1.9-fold, respectively, whereas α1mRNA was elevated by 2.0-fold at 24 h postexercise ( P = 0.036). A significant time main effect was found for α3protein abundance ( P = 0.046). Exercise transiently depressed maximal Na+-K+-ATPase activity ( P = 0.004), but Na+-K+-ATPase content was unaltered throughout recovery. Exercise immediately increased RNAP II mRNA by 2.6-fold ( P = 0.011) but had no effect on eIF-4E and 4E-BP1 mRNA. Thus a single bout of prolonged submaximal exercise induced isoform-specific Na+-K+-ATPase responses, increasing α1, α3, and β2mRNA but only α3protein expression. Exercise also increased mRNA expression of RNAP II, a gene initiating transcription, but not of eIF-4E and 4E-BP1, key genes initiating protein translation.
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Affiliation(s)
- K T Murphy
- Muscle, Ions, and Exercise Group, School of Human Movement, Recreation and Performance, Victoria University of Technology, Melbourne, Victoria, Australia
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Petersen AC, Murphy KT, Snow RJ, Leppik JA, Aughey RJ, Garnham AP, Cameron-Smith D, McKenna MJ. Depressed Na+-K+-ATPase activity in skeletal muscle at fatigue is correlated with increased Na+-K+-ATPase mRNA expression following intense exercise. Am J Physiol Regul Integr Comp Physiol 2005; 289:R266-74. [PMID: 15790751 DOI: 10.1152/ajpregu.00378.2004] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We investigated whether depressed muscle Na+-K+-ATPase activity with exercise reflected a loss of Na+-K+-ATPase units, the time course of its recovery postexercise, and whether this depressed activity was related to increased Na+-K+-ATPase isoform gene expression. Fifteen subjects performed fatiguing, knee extensor exercise at ∼40% maximal work output per contraction. A vastus lateralis muscle biopsy was taken at rest, fatigue, 3 h, and 24 h postexercise and analyzed for maximal Na+-K+-ATPase activity via 3- O-methylfluorescein phosphatase (3- O-MFPase) activity, Na+-K+-ATPase content via [3H]ouabain binding sites, and Na+-K+-ATPase α1-, α2-, α3-, β1-, β2- and β3-isoform mRNA expression by real-time RT-PCR. Exercise [352 (SD 267) s] did not affect [3H]ouabain binding sites but decreased 3- O-MFPase activity by 10.7 (SD 8)% ( P < 0.05), which had recovered by 3 h postexercise, without further change at 24 h. Exercise elevated α1-isoform mRNA by 1.5-fold at fatigue ( P < 0.05). This increase was inversely correlated with the percent change in 3- O-MFPase activity from rest to fatigue (%Δ3- O-MFPaserest-fatigue) ( r = −0.60, P < 0.05). The average postexercise (fatigue, 3 h, 24 h) α1-isoform mRNA was increased 1.4-fold ( P < 0.05) and approached a significant inverse correlation with %Δ3- O-MFPaserest-fatigue( r = −0.56, P = 0.08). Exercise elevated α2-isoform mRNA at fatigue 2.5-fold ( P < 0.05), which was inversely correlated with %Δ3- O-MFPaserest-fatigue( r = −0.60, P = 0.05). The average postexercise α2-isoform mRNA was increased 2.2-fold ( P < 0.05) and was inversely correlated with the %Δ3- O-MFPaserest-fatigue( r = −0.68, P < 0.05). Nonsignificant correlations were found between %Δ3- O-MFPaserest-fatigueand other isoforms. Thus acute exercise transiently decreased Na+-K+-ATPase activity, which was correlated with increased Na+-K+-ATPase gene expression. This suggests a possible signal-transduction role for depressed muscle Na+-K+-ATPase activity with exercise.
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Affiliation(s)
- A C Petersen
- Muscle, Ions and Exercise Group, School of Human Movement, Recreation and Performance, Centre for Ageing, Rehabilitation, Exercise, and Sport, Victoria University of Technology, PO Box 14428, MCMC, Melbourne, Victoria, Australia 8001
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9
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Wetzel RK, Pascoa JL, Arystarkhova E. Stress-induced expression of the gamma subunit (FXYD2) modulates Na,K-ATPase activity and cell growth. J Biol Chem 2004; 279:41750-7. [PMID: 15280368 DOI: 10.1074/jbc.m405622200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
In kidney, the Na,K-ATPase is associated with a single span protein, the gamma subunit (FXYD2). Two splice variants are differentially expressed along the nephron and have a differential influence on Na,K-ATPase when stably expressed in mammalian cells in culture. Here we used a combination of gene induction and gene silencing techniques to test the functional impact of gamma by means other than transfection. NRK-52E cells (of proximal tubule origin) do not express gamma as a protein under regular tissue culture conditions. However, when they were exposed to hyperosmotic medium, induction of only the gammaa splice variant was observed, which was accompanied by a reduction in the rate of cell division. Kinetic analysis of stable enzyme properties from control (alpha1beta1) and hypertonicity-treated cultures (alpha1beta1gammaa) revealed a significant reduction (up to 60%) of Na,K-ATPase activity measured under V(max) conditions with little or no change in the amounts of alpha1beta1. This effect as well as the reduction in cell growth rate was practically abolished when gamma expression was knocked down using specific small interfering RNA duplexes. Surprisingly, a similar induction of endogenous gammaa because of hypertonicity was seen in rat cell lines of other than renal origin: C6 (glioma), PC12 (pheochromocytoma), and L6 (myoblasts). Furthermore, exposure of NRK-52E cells to other stress inducers such as heat shock, exogenous oxidation, and chemical stress also resulted in a selective induction of gammaa. Taken together, the data imply that induction of gammaa may have adaptive value by being a part of a general cellular response to genotoxic stress.
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Affiliation(s)
- Randall K Wetzel
- Laboratory of Membrane Biology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
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Shao Y, Ismail-Beigi F. Control of Na+-K+-ATPase beta 1-subunit expression: role of 3'-untranslated region. Am J Physiol Cell Physiol 2004; 286:C580-5. [PMID: 14761885 DOI: 10.1152/ajpcell.00117.2003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Using in vitro translation and cell transfection assays, we previously demonstrated that the Na+ -K+ -ATPase beta1 mRNA species containing its longest 3'-untranslated region (UTR) exhibited the lowest translational efficiency. Here, employing deletions and in vivo expression assays, using direct injection of plasmids into rat ventricular myocardium, we identified a 143-nt segment located in the distal 3'-UTR of beta1 mRNA that was associated with decreased luciferase expression; interestingly, this segment contains three AUUUA motifs. Using RNA-protein binding assays and UV cross-linking of cRNA with cytosolic proteins of rat heart, we identified an approximately 38-kDa protein that specifically bound to the cRNA encoding the 143-nt segment of beta1 mRNA 3'-UTR. Mutation of three nucleotides located in the middle region of the 143-nt segment, which was predicted to greatly disrupt a putative stem-loop structure of the cRNA in this region, was associated with reduced binding of the mutated cRNA to the protein migrating at approximately 38 kDa. The cRNA encoding a segment of cyclooxygenase-2 mRNA 3'-UTR containing six AUUUA sequences did not bind the protein migrating at approximately 38 kDa and did not compete with the binding of the wild-type 143-nt beta(1) cRNA to the protein. The above results suggest that the 143-nt segment in the distal segment of the 3'-UTR of beta1 mRNA may play an important role in the control of beta1-subunit expression.
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Affiliation(s)
- Yvonne Shao
- Departments of Medicine and Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106-4951, USA
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Queiroz MS, Shao Y, Ismail-Beigi F. Effect of thyroid hormone on uncoupling protein-3 mRNA expression in rat heart and skeletal muscle. Thyroid 2004; 14:177-85. [PMID: 15072699 DOI: 10.1089/105072504773297849] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Thyroid hormones (triiodothyronine [T3] and thyroxine [T4]) stimulate UCP-3 expression in skeletal muscle. We examined whether thyroid hormone-induced changes in uncoupling protein (UCP)-3 mRNA expression are related to directs effects of T3 or reflect secondary effects of the hormone through stimulation of renin-angiotensin or beta-adrenergic systems. Hyperthyroidism was produced by three injections of 100 microg T3/100 g body weight on alternate days with or without concomitant treatment with either captopril (an angiotensin-converting enzyme [ACE] inhibitor), propranolol (a beta-blocker) or clenbuterol (a beta2-agonist). The relative abundance of UCP-3 mRNA was measured in ventricular myocardium and skeletal muscle (gastrocnemius and soleus). T3 resulted in a significant increase in the relative abundance of UCP-3 in heart and skeletal muscle (p < 0.05), and the effect was not altered by captopril or propanolol; the inhibitors alone had no effect of UCP-3 mRNA content. There was no synergistic or additive effect of T3 and clenbuterol on UCP-3 mRNA expression in skeletal muscle. Increased UCP-3 mRNA levels were associated with increased UCP-3 protein expression in skeletal muscle. We conclude that the effect of T3 on UCP-3 expression in cardiac and skeletal muscle is not dependent on either angiotensin II or the beta-adrenergic system and probably reflects a direct action of the hormone on UCP-3 gene expression.
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Affiliation(s)
- Marcia Silva Queiroz
- Department of Medicine and of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106-4951, USA
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Zhou X, Yin W, Doi SQ, Robinson SW, Takeyasu K, Fan X. Stimulation of Na,K-ATPase by low potassium requires reactive oxygen species. Am J Physiol Cell Physiol 2003; 285:C319-26. [PMID: 12686517 DOI: 10.1152/ajpcell.00536.2002] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The signaling pathway that transduces the stimulatory effect of low K+ on the biosynthesis of Na,K-ATPase remains largely unknown. The present study was undertaken to examine whether reactive oxygen species (ROS) mediated the effect of low K+ in Madin-Darby canine kidney (MDCK) cells. Low K+ increased ROS activity in a time- and dose-dependent manner, and this effect was abrogated by catalase and N-acetylcysteine (NAC). To determine the role of ROS in low-K+-induced gene expression, the cells were first stably transfected with expression constructs in which the reporter gene chloramphenicol acetyl transferase (CAT) was under the control of the avian Na,K-ATPase alpha-subunit 1.9 kb and 900-bp 5'-flanking regions that have a negative regulatory element. Low K+ increased the CAT expression in both constructs. Catalase or NAC inhibited the effect of low K+. To determine whether the increased CAT activity was mediated through releasing the repressive effect or a direct stimulation of the promoter, the cells were transfected with a CAT expression construct directed by a 96-bp promoter fragment that has no negative regulatory element. Low K+ also augmented the CAT activity expressed by this construct. More importantly, both catalase and NAC abolished the effect of low K+. Moreover, catalase and NAC also inhibited low-K+-induced increases in the Na,K-ATPase alpha1- and beta1-subunit protein abundance and ouabain binding sites. The antioxidants had no significant effect on the basal levels of CAT activity, protein abundance, or ouabain binding sites. In conclusion, low K+ enhances the Na,K-ATPase gene expression by a direct stimulation of the promoter activity, and ROS mediate this stimulation and also low-K+-induced increases in the Na,K-ATPase protein contents and cell surface molecules.
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Affiliation(s)
- Xiaoming Zhou
- Department of Medicine, Uniformed Services University, 4301 Jones Bridge Rd., Bethesda, MD 20814, USA.
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Young DB, McCabe RD. Endocrine Control of Potassium Balance. Compr Physiol 2000. [DOI: 10.1002/cphy.cp070308] [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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Kometiani P, Tian J, Li J, Nabih Z, Gick G, Xie Z. Regulation of Na/K-ATPase beta1-subunit gene expression by ouabain and other hypertrophic stimuli in neonatal rat cardiac myocytes. Mol Cell Biochem 2000; 215:65-72. [PMID: 11204457 DOI: 10.1023/a:1026503319387] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Partial inhibition of Na/K-ATPase by ouabain causes hypertrophic growth and regulates several early and late response genes, including that of Na/K-ATPase alpha3 subunit, in cultured neonatal rat cardiac myocytes. The aim of this work was to determine whether ouabain and other hypertrophic stimuli affect Na/K-ATPase beta1 subunit gene expression. When myocytes were exposed to non-toxic concentrations of ouabain, ouabain increased beta1 subunit mRNA in a dose- and time-dependent manner. Like the alpha3 gene, beta1 mRNA was also regulated by several other well-known hypertrophic stimuli including phenylephrine, a phorbol ester, endothelin-1, and insulin-like growth factor, suggesting involvement of growth signals in regulation of beta1 expression. Ouabain failed to increase beta1 subunit mRNA in the presence of actinomycin D. Using a luciferase reporter gene that is directed by the 5'-flanking region of the beta1 subunit gene, transient transfection assay showed that ouabain augmented the expression of luciferase. These data support the proposition that ouabain regulates the beta1 subunit through a transcriptional mechanism. The effect of ouabain on beta1 subunit induction, like that on alpha3 repression, was dependent on extracellular Ca2+ and on calmodulin. Inhibitions of PKC, Ras, and MEK, however, had different quantitive effects on ouabain-induced regulations of beta1 and alpha3 subunits. The findings show that partial inhibition of Na/K-ATPase activates multiple signaling pathways that regulate growth-related genes, including those of two subunit isoforms of Na/K-ATPase, in a gene-specific manner.
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Affiliation(s)
- P Kometiani
- Department of Pharmacology, Medical College of Ohio, Toledo 43614-5804, USA
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Zhuang Y, Wendt C, Gick G. Regulation of Na,K-ATPase beta 1 subunit gene transcription by low external potassium in cardiac myocytes. Role of Sp1 AND Sp3. J Biol Chem 2000; 275:24173-84. [PMID: 10811658 DOI: 10.1074/jbc.m002953200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Expression of Na,K-ATPase activity is up-regulated in cells incubated for extended intervals in the presence of low external K(+). Our previous data showed that exposure of cardiac myocytes to low K(+) increased the steady-state abundance of Na,K-ATPase beta1 subunit mRNA. In the present study we determined that incubation of primary cultures of neonatal rat cardiac myocytes with low K(+) augmented Na,K-ATPase beta1 gene expression at a transcriptional level and that this effect required extracellular Ca(2+). The stimulatory effect of low K(+) on Na,K-ATPase beta1 gene transcription was not dependent on increased contractile activity of cardiac myocytes. Na,K-ATPase beta1 5'-flanking region deletion plasmids used in transient transfection analysis demonstrated that the region between nucleotides -62 to -42 of the beta1 promoter contained a low K(+) response element. Site-directed mutagenesis of a potential GC box core motif GCG in the -58/-56 region of the beta1 promoter decreased basal and low K(+)-mediated transcription. Mutation of the core sequence of a putative GC box element located between nucleotides -101 and -99 further decreased the low K(+) effect on beta1 gene transcription. Electrophoretic mobility shift assays using oligonucleotides spanning the proximal and distal GC box elements of the beta1 promoter showed enhanced binding of two complexes in response to low K(+). The inclusion of a consensus GC box sequence as a competitor in gel shift analysis reduced factor binding to the low K(+) response elements. Antibodies to transcription factors Sp1 and Sp3 interacted with components of both DNA-binding complexes and binding of nuclear factors was abolished in gel shift studies using GC box mutants. Together these data indicate that enhanced binding of Sp1 and Sp3 to two GC box elements in the rat Na,K-ATPase beta1 subunit gene promoter mediates beta1 gene transcription up-regulation in neonatal rat cardiac myocytes exposed to low external K(+).
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Affiliation(s)
- Y Zhuang
- Department of Biochemistry and Center for Cardiovascular and Muscle Research, State University of New York Health Science Center at Brooklyn, Brooklyn, New York 11203, USA
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16
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Orlov SN, Taurin S, Thorin-Trescases N, Dulin NO, Tremblay J, Hamet P. Inversion of the intracellular Na(+)/K(+) ratio blocks apoptosis in vascular smooth muscle cells by induction of RNA synthesis. Hypertension 2000; 35:1062-8. [PMID: 10818065 DOI: 10.1161/01.hyp.35.5.1062] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
This study examines the involvement of RNA and protein synthesis in the modulation of apoptosis in vascular smooth muscle cells (VSMC) by intracellular monovalent cations. In VSMC transfected with E1A adenovirus (VSMC-E1A), inversion of the [Na(+)](i)/[K(+)](i) ratio by an inhibitor of the Na(+),K(+) pump, ouabain, prevented the development of apoptosis triggered by serum withdrawal. Inhibition of apoptosis by ouabain was abolished by inhibitors of RNA and protein synthesis, actinomycin D, and cycloheximide, respectively. In VSMC-E1A, incubation with ouabain for 4 and 24 hours augmented RNA synthesis by 20% to 50% and 3-fold to 4-fold, respectively. In quiescent VSMC, the effect of ouabain and serum on RNA synthesis was additive. Ouabain did not affect the level of phosphorylation of ERK, JNK, and p38 MAP kinases and blocked apoptosis independent of the presence of the MAPK kinase inhibitors PD98059 and SB 202190. Equimolar substitution of NaCl with KCl in the incubation medium abolished the effect of ouabain on intracellular Na(+) and K(+) concentration, apoptosis, and RNA synthesis. Thus, our results demonstrate that the antiapoptotic effect of the inverted [Na(+)](i)/[K(+)](i) ratio is mediated by MAPK-independent induction of de novo synthesis of RNA species encoding inhibitor(s) of programmed cell death.
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Affiliation(s)
- S N Orlov
- Centre de Recherché du CHUM, Campus Hotel-Dieu, University of Montreal, Montreal, PQ, Canada.
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17
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Sennoune S, Gerbi A, Duran MJ, Grillasca JP, Compe E, Pierre S, Planells R, Bourdeaux M, Vague P, Pieroni G, Maixent JM. Effect of streptozotocin-induced diabetes on rat liver Na+/K+-ATPase. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:2071-8. [PMID: 10727947 DOI: 10.1046/j.1432-1327.2000.01211.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Na+/K+-ATPase during diabetes may be regulated by synthesis of its alpha and beta subunits and by changes in membrane fluidity and lipid composition. As these mechanisms were unknown in liver, we studied in rats the effect of streptozotocin-induced diabetes on liver Na+/K+-ATPase. We then evaluated whether fish oil treatment prevented the diabetes-induced changes. Diabetes mellitus induced an increased Na+/K+-ATPase activity and an enhanced expression of the beta1 subunit; there was no change in the amount of the alpha1 and beta3 isoenzymes. Biphasic ouabain inhibition curves were obtained for diabetic groups indicating the presence of low and high affinity sites. No alpha2 and alpha3 isoenzymes could be detected. Diabetes mellitus led to a decrease in membrane fluidity and a change in membrane lipid composition. The diabetes-induced changes are not prevented by fish oil treatment. The results suggest that the increase of Na+/K+-ATPase activity can be associated with the enhanced expression of the beta1 subunit in the diabetic state, but cannot be attributed to changes in membrane fluidity as typically this enzyme will increase in response to an enhancement of membrane fluidity. The presence of a high-affinity site for ouabain (IC50 = 10-7 M) could be explained by the presence of (alphabeta)2 diprotomeric structure of Na+/K+-ATPase or an as yet unknown alpha subunit isoform that may exist in diabetes mellitus. These stimulations might be related, in part, to the modification of fatty acid content during diabetes.
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Affiliation(s)
- S Sennoune
- Laboratoire de Recherche Cardiologique, Faculté de Medecine Nord, Marseille, France
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18
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Muto S, Nemoto J, Okada K, Miyata Y, Kawakami K, Saito T, Asano Y. Intracellular Na+ directly modulates Na+,K+-ATPase gene expression in normal rat kidney epithelial cells. Kidney Int 2000; 57:1617-35. [PMID: 10760097 DOI: 10.1046/j.1523-1755.2000.00006.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
BACKGROUND In a wide variety of cell systems, increases in cell Na+ ([Na+]i) lead to an induction of N+,K+-ATPase mRNA expression. On the other hand, the increase in [Na+]i can also induce a rise in cell Ca2+ ([Ca2+]i) through a secondary inhibition of Na+/Ca2+ exchange and a decrease in cell pH (pHi) through a secondary inhibition of Na+/H+ exchange. It is not known whether [Na+]i, [Ca2+]i, and/or pHi directly modulate N+,K+-ATPase mRNA expression. METHODS We used normal rat kidney epithelial cells (NRK) to examine the effects of ouabain on N+,K+-ATPase alpha1- and beta1-mRNA accumulation by Northern blot analysis and the relationship between the mRNA accumulation and [Na+]i, [Ca2+]i, or pHi. [Na+]i, [Ca2+]i, and pHi were measured using a Na+-sensitive fluorescent dye (SBFI), a Ca2+-sensitive fluorescent dye (Fura-2), and a pH-sensitive fluorescent dye (BCECF), respectively. RESULTS Ouabain (1 mmol/L) significantly increased [Na+]i. Upon addition of ouabain, alpha1-mRNA levels increased to 2. 3 times the control level at three hours, with maximum 3.3-fold elevations at 12 hours. beta1-mRNA levels also increased to 2.4 times the control level at 3 hours, with a maximum 3.3-fold increase at 12 hours. The ouabain-mediated alpha1- and beta1-mRNA induction was inhibited by both the RNA transcription inhibitor (actinomycin D) and the protein synthesis inhibitor (cycloheximide). Ouabain at three hours caused an increase in [Ca2+]i. Similar increases in [Ca2+]i, which were elicited by the Ca2+ ionophore (ionomycin) in the presence of extracellular Ca2+, had no effect on alpha1- or beta1-mRNA levels. In Ca2+-free medium treated with EGTA, ouabain at three hours caused a significant increase in [Na+]i without any changes in [Ca2+]i, and also increased alpha1- and beta1-mRNA levels. Ouabain at three hours caused a significant decrease in pHi. Similar decreases in pHi, which were elicited by the specific inhibitor of Na+/H+ exchange (ethylisopropylamiloride), caused no effect on alpha1- or beta1-mRNA levels. Exposure of NRK to the Na+ ionophore (monensin) in the absence of extracellular Ca2+ increased [Na+]i and alpha1- and beta1-mRNA levels. The increases in alpha1- and beta1-mRNA levels upon addition of ouabain were associated with significant increases in alpha1- and beta1-subunit proteins. CONCLUSIONS In NRK, ouabain causes an increase in [Na+]i, which directly modulates Na+,K+-ATPase alpha1- and beta1-mRNA accumulation.
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Affiliation(s)
- S Muto
- Department of Nephrology, Endocrinology and Metabolism, and Biology, Jichi Medical School, Minamikawachi, Tochigi, Japan.
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19
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Nguyen AT, Hayward-Lester A, Sabatini S, Doris PA. Renal Na+, K+-ATPase in SHR: studies of activity and gene expression. Clin Exp Hypertens 1998; 20:641-56. [PMID: 9682920 DOI: 10.3109/10641969809053242] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The mechanism by which increased dietary intake of calcium reduces blood pressure in the spontaneously hypertensive rat is unknown. The present studies were designed to determine if there were alterations in the activity of the major membrane ion translocating pump, sodium, potassium-ATPase (NKA), in the kidneys of hypertensive rats and whether increased dietary calcium intake affected the activity of this enzyme. Fifteen-week old SHR's were found to have lower total ATPase activity in microsomal preparations from the kidney than age matched Wistar-Kyoto animals. Both the ouabain-sensitive component (NKA) and the ouabain-insensitive component were lower in SHR. Increasing dietary calcium intake from 1% to 3% elevated both components of the ATPase activity in SHR, but was without effect in WKY. Measurement of membrane phospholipid composition suggested that altered phospholipid composition did not account for the reduced ATPase activity observed, but indicated a reduced density of ATPase in SHR. A technique has been devised for qualitative and quantitative analysis of Na, K-ATPase alpha isoforms using RT-PCR. This technique reveals that the alpha 1 isoform is the sole catalytic isoform present in the nephron. Accurate and precise quantification of the amount of gene expression in individual nephron segments is reported and will be applied to determine whether dietary calcium influences blood pressure by a mechanism which alters nephron NKA gene expression.
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Affiliation(s)
- A T Nguyen
- Institute of Molecular Medicine, University of Texas Health Science Center, Houston 77030, USA
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20
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Liu X, Hymel LJ, Songu-Mize E. Role of Na+ and Ca2+ in stretch-induced Na(+)-K(+)-ATPase alpha-subunit regulation in aortic smooth muscle cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:H83-9. [PMID: 9458855 DOI: 10.1152/ajpheart.1998.274.1.h83] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
This study was designed to test the role of Na+ and Ca2+ entry in the stretch-induced Na(+)-K(+)-ATPase alpha 1- and alpha 2-isoform upregulation observed in our previous studies. We measured intracellular Na+ in cyclically stretched rat aortic smooth muscle cells, with or without gadolinium treatment, for various durations and performed Western blotting to analyze the effects of stretch and the calcium channel blocker isradipine on the expression of alpha-isoforms. Intracellular Na+ was elevated significantly after 1- and 2-h stretch, but returned to baseline after 1-, 2-, and 4-day stretch. This increase in intracellular Na+ was blocked by gadolinium. Both alpha 1- and alpha 2-isoforms were upregulated after either 2 or 4 days of cyclical stretch. Isradipine had no apparent effect on stretch-induced upregulation on either alpha-isoform, thus suggesting that Ca2+ entry through L-type channels is not involved in the stretch-induced upregulation. We therefore conclude that a transient intracellular Na+ elevation during stretch may serve as a signal to mediate the alpha 1- and alpha 2-isoform upregulation.
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MESH Headings
- Animals
- Aorta/enzymology
- Aorta/physiology
- Calcium/metabolism
- Calcium Channel Blockers/pharmacology
- Calcium Channels/physiology
- Calcium Channels, L-Type
- Cells, Cultured
- Gadolinium/pharmacology
- Gene Expression Regulation, Enzymologic/drug effects
- Gene Expression Regulation, Enzymologic/physiology
- Isoenzymes/biosynthesis
- Isradipine/pharmacology
- Kinetics
- Macromolecular Substances
- Male
- Muscle, Smooth, Vascular/enzymology
- Muscle, Smooth, Vascular/physiology
- Rats
- Rats, Sprague-Dawley
- Sodium/metabolism
- Sodium-Potassium-Exchanging ATPase/biosynthesis
- Stress, Mechanical
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Affiliation(s)
- X Liu
- Department of Pharmacology and Experimental Therapeutics, Louisiana State University Medical Center, New Orleans, USA
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21
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Dunn JF, Burton KA, Dauncey MJ. Ouabain sensitive Na+/K(+)-ATPase content is elevated in mdx mice: implications for the regulation of ions in dystrophic muscle. J Neurol Sci 1995; 133:11-5. [PMID: 8583212 DOI: 10.1016/0022-510x(95)00167-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Recent evidence indicates that in dystrophin-deficient muscle, intracellular sodium content (Na(i)) may be elevated and sodium regulation may be altered or impaired. If there is an elevation in Na(i), this could be due to decreased active pumping of sodium from the cell or increased passive influx of sodium. The present study has therefore determined the content of plasma membrane-bound Na+/K(+)-ATPase in the skeletal muscle of mdx mice; a genetically homologous model of Duchenne muscular dystrophy. Measurements were made on muscles from 5-6-month-old mdx mice and age-matched controls of the C57B1/10ScSn strain (n = 9 pairs), using the vanadate-facilitated ouabain-binding technique. The Na+/K(+)-ATPase concentration per unit weight increased by 2.3-fold in the longissimus dorsi and 1.4-fold in the gastrocnemius of mdx mice compared with controls. The increase in Na+/K(+)-ATPase content is of similar magnitude to the previously reported increase in ouabain-sensitive Na+/K(+)-ATPase activity in mdx muscle, suggesting that this elevated enzyme activity occurs largely through an increase in its concentration. This compensatory increase in the main regulator of internal sodium is likely to occur in an attempt to maintain homeostasis. Nevertheless, the elevated pump concentration is unable to compensate entirely for the increased Na(i). These results are consistent with a previously proposed hypothesis that sodium regulation is abnormal in dystrophin deficient muscles, and also that cell death in these muscles may be due to abnormal regulation of cell volume.
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Affiliation(s)
- J F Dunn
- MRC Biochemical and Clinical Magnetic Resonance Unit, Oxford, UK.
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22
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Celsi G, Wang ZM. Regulation of Na+,K(+)-ATPase gene expression: a model to study terminal differentiation. Pediatr Nephrol 1993; 7:630-4. [PMID: 8251337 DOI: 10.1007/bf00852570] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
This review focuses on the ontogeny of factors involved in the transcriptional regulation of Na+,K(+)-ATPase expression. The Na+,K(+)-ATPase enzyme is of vital importance for cell function. It is likely that the limited availability of Na+,K(+)-ATPase in infant tissue is the major limiting factor for adaptation to extra-uterine life in several organs. The factors regulating Na+,K(+)-ATPase gene transcription in infancy are discussed. Special emphasis is given to the role of circulating hormones such as glucocorticoids and thyroxine.
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Affiliation(s)
- G Celsi
- Department of Paediatrics, St. Göran's Children's Hospitals, Karolinska Institutet, Stockholm, Sweden
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23
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Yamamoto K, Ikeda U, Seino Y, Tsuruya Y, Oguchi A, Okada K, Ishikawa S, Saito T, Kawakami K, Hara Y. Regulation of Na,K-adenosine triphosphatase gene expression by sodium ions in cultured neonatal rat cardiocytes. J Clin Invest 1993; 92:1889-95. [PMID: 8408640 PMCID: PMC288354 DOI: 10.1172/jci116781] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Na,K-ATPase (Na,K-pump) plays an important role in the regulation of intracellular ion composition. The purpose of this study is to determine whether Na+ regulates the levels of mRNA coding for Na,K-ATPase alpha and beta subunits in cultured neonatal rat cardiocytes. We measured intracellular Na+ levels ([Na+]i) in cardiocytes using a Na(+)-sensitive fluorescence dye (SBFI). 1 mM ouabain caused a significant increase in [Na+]i in cardiocytes; from 12.8 +/- 0.3 to 28.8 +/- 1.8 mM. Exposure of cardiocytes to 1 mM ouabain resulted in a three- to fourfold increase in alpha 1, alpha 2, and alpha 3 mRNA accumulation, and an approximate two-fold increase in beta 1 mRNA accumulation. A maximum elevation was reached at 60 min in both cases. The ouabain-induced alpha 1 mRNA accumulation was still observed in the Ca(2+)-free culture medium. Exposure of cardiocytes to 10 microM monensin in the absence of extracellular Ca2+ also resulted in a threefold increase in alpha 1 mRNA accumulation. The increased alpha 1 mRNA expression by 1 mM ouabain was associated with a fourfold increase in alpha 1 subunit protein accumulation. Transfection experiments with chimeric plasmids containing 5'-flanking sequences of alpha 1, alpha 2, and alpha 3 isoform genes and a luciferase reporter gene revealed that 1 mM ouabain caused a twofold increase in luciferase activity in each alpha system. These results suggest that Na+ directly regulates Na,K-ATPase gene expression in cardiocytes. The transfection study further supports the premise that Na(+)-responsive elements are located within the 5'-flanking sequences of each alpha isoform gene.
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Affiliation(s)
- K Yamamoto
- Department of Cardiology, Jichi Medical School, Tochigi, Japan
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24
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Higham SC, Melikian J, Karin NJ, Ismail-Beigi F, Pressley TA. Na,K-ATPase expression in C2C12 cells during myogenesis: minimal contribution of alpha 2 isoform to Na,K transport. J Membr Biol 1993; 131:129-36. [PMID: 8382748 DOI: 10.1007/bf02791321] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Cells of the murine skeletal muscle line, C2C12, undergo differentiation from mononuclear myoblasts to multinuclear myotubes that express a number of proteins associated with striated muscle. We examined the relationship between the abundance of the mRNAs encoding the fast-twitch Ca-ATPase and the alpha isoforms of Na,K-ATPase and the subsequent expression of their respective polypeptides. Both the mRNA and protein levels of the alpha 1 isoform remained constant throughout differentiation. In contrast, the content of mRNAs encoding the alpha 2 isoform and fast-twitch Ca-ATPase increased coordinately with the abundance of their corresponding polypeptides during myotube development. Despite the dramatic increase in alpha 2 expression, estimates of in vitro Na,K-ATPase activity and assessments of in vivo transport activity suggest that alpha 2 contributes little to ionic homeostasis in C2C12 myotubes.
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Affiliation(s)
- S C Higham
- Department of Physiology and Cell Biology, University of Texas Medical School, Houston 77225
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25
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Abstract
Preimplantation development encompasses the "free"-living period of mammalian embryogenesis, which culminates in the formation of a fluid-filled structure, the blastocyst. Cavitation (blastocyst formation) is accompanied by the expression of a novel set of gene products that contribute directly to the attainment of cell polarity with the trophectoderm, which is both the first epithelium of development and the outer cell layer encircling the inner cell mass of the blastocyst. Several of these gene products have been identified and include the tight junction (ZO-1), Na/K-ATPase (alpha and beta subunits), uvomorulin, gap junction (connexin43), and growth factors such as transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF). This review will examine the role(s) of each of these gene products during the onset and progression of blastocyst formation. The trophectodermal tight junctional permeability seal regulates the leakage of blastocoel fluid and also assists in the maintenance of a polarized Na/K-ATPase distribution to the basolateral plasma membrane domain of the mural trophectoderm. The polarized distribution of the Na/K-ATPase plays an integral role in the establishment of a trans-trophectoderm Na+ gradient, which drives the osmotic accumulation of water across the epithelium into the nascent blastocoelic cavity. The cell adhesion provided by uvomorulin is necessary for the establishment of the tight junctional seal, as well as the maintenance of the polarized Na/K-ATPase distribution. Growth factors such as TGF-alpha and EGF stimulate an increase in the rate of blastocoel expansion, which could, in part, be mediated by secondary messengers that result in an increase in Na/K-ATPase activity. Insight into the mechanism of cavitation has, therefore, directly linked blastocyst formation to trophectoderm cell differentiation, which arises through fundamental cell biological processes that are directly involved in the attainment of epithelial cell polarity.
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Affiliation(s)
- A J Watson
- Department of Medical Biochemistry, University of Calgary Health Sciences Center, Alberta, Canada
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26
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Devarajan P, Gilmore-Hebert M, Benz EJ. Differential translation of the Na,K-ATPase subunit mRNAs. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)41690-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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27
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Mata M, Hieber V, Beaty M, Clevenger M, Fink DJ. Activity-dependent regulation of Na+, K(+)-ATPase alpha isoform mRNA expression in vivo. J Neurochem 1992; 59:622-6. [PMID: 1321232 DOI: 10.1111/j.1471-4159.1992.tb09415.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
To investigate the functional role of the different Na+, K(+)-ATPase alpha (catalytic) subunit isoforms in neuronal cells, we used quantitative in situ hybridization with riboprobes specific for alpha 1, alpha 2, and alpha 3 isoforms to measure the level of alpha isoform-specific expression in the neuroendocrine cells of the supraoptic (SON) and paraventricular (PVN) nuclei of rat hypothalamus. A prolonged increase in electrical activity of these cells, achieved by 5 days of salt treatment, increased the amount of alpha 1 isoform mRNA in the SON and PVN by 50%. Levels of alpha 1 mRNA in other brain regions and levels of alpha 2 and alpha 3 mRNAs were not affected by salt treatment. We conclude that the alpha 1 isoform Na+, K(+)-ATPase may be specifically adapted to pump out Na+, which enters the cells through voltage-gated channels during neuronal depolarization.
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Affiliation(s)
- M Mata
- Department of Neurology, University of Michigan, Ann Arbor
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28
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Bhutada A, Wassynger W, Ismail-Beigi F. Dexamethasone markedly induces Na,K-ATPase mRNA beta 1 in a rat liver cell line. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)99098-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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29
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Swann AC. Brain Na+,K(+)-ATPase regulation in vivo: reduction in activity and response to sodium by intracerebroventricular tetrodotoxin. Brain Res 1991; 543:251-5. [PMID: 1647832 DOI: 10.1016/0006-8993(91)90035-t] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We investigated the effects of intracerebroventricular infusion of tetrodotoxin on activity and function of brain Na+,K(+)-ATPase. Infusion of 1 or 3 micrograms/h for 2, 4 or 7 days by osmotic minipump reduced the number of Na+,K(+)-ATPase sites as measured by ouabain binding in cerebral cortex. Tetrodotoxin infusions substantially reduced the functional transport capacity of Na+,K(+)-ATPase, measured by the maximal increase in synaptoneurosomal 86Rb+ uptake in the presence of monensin. The effects were maximal at 4 days, with a possible partial recovery of activity at 7 days. Results of ouabain inhibition curves suggested that the effect of tetrodotoxin was not specific for enzyme with high or low affinity for ouabain.
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Affiliation(s)
- A C Swann
- Department of Psychiatry, University of Texas Medical School, Houston 77225
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30
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Hsu YM, Guidotti G. Effects of hypokalemia on the properties and expression of the (Na+,K+)-ATPase of rat skeletal muscle. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)52452-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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31
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Lescale-Matys L, Hensley CB, Crnkovic-Markovic R, Putnam DS, McDonough AA. Low K+ increases Na,K-ATPase abundance in LLC-PK1/Cl4 cells by differentially increasing beta, and not alpha, subunit mRNA. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(18)38253-x] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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32
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Gick GG, Melikian J, Ismail-Beigi F. Thyroidal enhancement of rat myocardial Na,K-ATPase: preferential expression of alpha 2 activity and mRNA abundance. J Membr Biol 1990; 115:273-82. [PMID: 2165172 DOI: 10.1007/bf01868642] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In hypothyroid rat myocardium, the low-ouabain-sensitivity Na,K-ATPase activity had a KI = 10(-4) M and accounted for approximately 95% of the enzyme activity, while the high-ouabain-sensitivity activity contributed approximately 5% to the total activity, with a KI = 3 x 10(-7) M. mRNA alpha 1 was 7.2- and 5.5-fold more abundant than mRNA alpha 2 and mRNA beta, respectively, in hypothyroid ventricles while mRNA alpha 3 was undetectable. Administration of T3 increased total Na,K-ATPase activity 1.6-fold; the low-ouabain-sensitivity activity increased 1.5-fold while high-ouabain-sensitivity activity was stimulated 3.2-fold. T3 increased the number of high-affinity ouabain-binding sites 2.9-fold with no change in Kd (approximately 2 x 10(-7) M). The abundances of mRNA alpha 1, mRNA alpha 2, and mRNA beta (per unit RNA) following T3 treatment increased 3.6-, 10.6-, and 12.7-fold, respectively. The larger increments in subunit mRNA abundances than in Na,K-ATPase activity suggests the involvement of translational and/or post-translational regulatory steps in Na,K-ATPase biogenesis in response to T3. It is concluded that T3 enhances myocardial Na,K-ATPase subunit mRNA abundances and Na,K-ATPase activity, and that the expression of the high- and low-ouabain-sensitivity activities are probably a reflection of the abundances of the alpha 2 and alpha 1 isoforms, respectively. The physiological role played by the beta subunit remains uncertain.
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Affiliation(s)
- G G Gick
- Department of Biochemistry and Molecular Biophysics, College of Physicians and Surgeons, Columbia University, New York, New York 10032
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Pre-translational regulation of the (Na+ + K+)-ATPase in response to demand for ion transport in cultured chicken skeletal muscle. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)39710-8] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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Swann AC, Steketee JD. Subacute noradrenergic agonist infusions in vivo increase Na+, K+-ATPase and ouabain binding in rat cerebral cortex. J Neurochem 1989; 52:1598-604. [PMID: 2540278 DOI: 10.1111/j.1471-4159.1989.tb09214.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In order to investigate the specificity of noradrenergic effects on Na+, K+-ATPase, we infused noradrenergic agonists into the cerebral ventricles of rats, with or without depletion of forebrain norepinephrine. Infusion of norepinephrine, isoproterenol, or phenylephrine increased ouabain binding in intact rats, whereas clonidine infusion decreased binding. Depletion of forebrain norepinephrine by destruction of the dorsal noradrenergic bundle reduced ouabain binding. Norepinephrine infusion reversed the effect of dorsal bundle lesion; isoproterenol and phenylephrine increased ouabain binding in lesioned rats, but did not restore the effect of the lesions. Clonidine had no effect in lesioned rats. Effects on Na+, K+-ATPase activity were similar, but smaller. These results suggest that stimulation of both alpha 1- and beta-noradrenergic receptors may be necessary for optimal Na+, K+-ATPase, and that clonidine reduces Na+, K+-ATPase indirectly through decreased norepinephrine release.
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Affiliation(s)
- A C Swann
- Department of Psychiatry, University of Texas Medical School, Houston 77225
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Affiliation(s)
- T A Pressley
- Department of Physiology and Cell Biology, University of Texas Medical School, Houston 77225
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