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Theillet FX, Luchinat E. In-cell NMR: Why and how? PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2022; 132-133:1-112. [PMID: 36496255 DOI: 10.1016/j.pnmrs.2022.04.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Revised: 04/19/2022] [Accepted: 04/27/2022] [Indexed: 06/17/2023]
Abstract
NMR spectroscopy has been applied to cells and tissues analysis since its beginnings, as early as 1950. We have attempted to gather here in a didactic fashion the broad diversity of data and ideas that emerged from NMR investigations on living cells. Covering a large proportion of the periodic table, NMR spectroscopy permits scrutiny of a great variety of atomic nuclei in all living organisms non-invasively. It has thus provided quantitative information on cellular atoms and their chemical environment, dynamics, or interactions. We will show that NMR studies have generated valuable knowledge on a vast array of cellular molecules and events, from water, salts, metabolites, cell walls, proteins, nucleic acids, drugs and drug targets, to pH, redox equilibria and chemical reactions. The characterization of such a multitude of objects at the atomic scale has thus shaped our mental representation of cellular life at multiple levels, together with major techniques like mass-spectrometry or microscopies. NMR studies on cells has accompanied the developments of MRI and metabolomics, and various subfields have flourished, coined with appealing names: fluxomics, foodomics, MRI and MRS (i.e. imaging and localized spectroscopy of living tissues, respectively), whole-cell NMR, on-cell ligand-based NMR, systems NMR, cellular structural biology, in-cell NMR… All these have not grown separately, but rather by reinforcing each other like a braided trunk. Hence, we try here to provide an analytical account of a large ensemble of intricately linked approaches, whose integration has been and will be key to their success. We present extensive overviews, firstly on the various types of information provided by NMR in a cellular environment (the "why", oriented towards a broad readership), and secondly on the employed NMR techniques and setups (the "how", where we discuss the past, current and future methods). Each subsection is constructed as a historical anthology, showing how the intrinsic properties of NMR spectroscopy and its developments structured the accessible knowledge on cellular phenomena. Using this systematic approach, we sought i) to make this review accessible to the broadest audience and ii) to highlight some early techniques that may find renewed interest. Finally, we present a brief discussion on what may be potential and desirable developments in the context of integrative studies in biology.
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Affiliation(s)
- Francois-Xavier Theillet
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France.
| | - Enrico Luchinat
- Dipartimento di Scienze e Tecnologie Agro-Alimentari, Alma Mater Studiorum - Università di Bologna, Piazza Goidanich 60, 47521 Cesena, Italy; CERM - Magnetic Resonance Center, and Neurofarba Department, Università degli Studi di Firenze, 50019 Sesto Fiorentino, Italy
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Skoblina MN. Role of hydration in ovulation of common frog oocytes in vitro. Russ J Dev Biol 2013. [DOI: 10.1134/s1062360413030065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Mohanty BK, Gupta BL. A marked animal-vegetal polarity in the localization of Na(+),K(+) -ATPase activity and its down-regulation following progesterone-induced maturation. Mol Reprod Dev 2011; 79:138-60. [PMID: 22213374 DOI: 10.1002/mrd.22012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2011] [Accepted: 11/22/2011] [Indexed: 01/01/2023]
Abstract
The stage-VI Xenopus oocyte has a very distinct animal-vegetal polarity with structural and functional asymmetry. In this study, we show the expression and distribution pattern of Na(+),K(+) -ATPase in stage-VI oocytes, and its changes following progesterone-induced maturation. Using enzyme-specific electron microscopy phosphatase histochemistry, [(3) H]-ouabain autoradiography, and immunofluorescence cytochemistry at light microscopic level, we find that Na(+),K(+) -ATPase activity is mainly confined to the animal hemisphere. Electron microscopy histochemical results also suggest that polarized distribution of Na(+),K(+) -ATPase activity persists following progesterone-induced maturation, and it becomes gradually more polarized towards the animal pole. The time course following progesterone-induced maturation suggests that there is an initial up-regulation and then gradual down-regulation of Na(+),K(+) -ATPase activity leading to germinal vesicle breakdown (GVBD). By GVBD, the Na(+),K(+) -ATPase activity is completely down-regulated due to endocytotic removal of pump molecules from the plasma membrane into the sub-cortical region of the oocyte. This study provides the first direct evidence for a marked asymmetric localization of Na(+),K(+) -ATPase activity in any vertebrate oocyte. Here, we propose that such asymmetry in Na(+),K(+) -ATPase activity in stage-VI oocytes, and their down-regulation following progesterone-induced maturation, is likely to have a role in the active state of the germinal vesicle in stage-VI oocytes and chromosomal condensation after GVBD.
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Baskind NE, McRae C, Sharma V, Fisher J. Understanding subfertility at a molecular level in the female through the application of nuclear magnetic resonance (NMR) spectroscopy. Hum Reprod Update 2010; 17:228-41. [DOI: 10.1093/humupd/dmq039] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
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5
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Zhang Y, Poirer-Quinot M, Springer CS, Balschi JA. Discrimination of intra- and extracellular 23Na+ signals in yeast cell suspensions using longitudinal magnetic resonance relaxography. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 205:28-37. [PMID: 20430659 PMCID: PMC2885488 DOI: 10.1016/j.jmr.2010.03.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2009] [Revised: 03/01/2010] [Accepted: 03/29/2010] [Indexed: 05/16/2023]
Abstract
This study tested the ability of MR relaxography (MRR) to discriminate intra- (Nai+) and extracellular (Nae+)23Na+ signals using their longitudinal relaxation time constant (T1) values. Na+-loaded yeast cell (Saccharomyces cerevisiae) suspensions were investigated. Two types of compartmental 23Na+T1 differences were examined: a selective Nae+T1 decrease induced by an extracellular relaxation reagent (RRe), GdDOTP5-; and, an intrinsic T1 difference. Parallel studies using the established method of 23Na MRS with an extracellular shift reagent (SRe), TmDOTP5-, were used to validate the MRR measurements. With 12.8 mM RRe, the 23Nae+T1 was 2.4 ms and the 23Nai+T1 was 9.5 ms (9.4 T, 24 degrees C). The Na+ amounts and spontaneous efflux rate constants were found to be identical within experimental error whether measured by MRR/RRe or by MRS/SRe. Without RRe, the Na+-loaded yeast cell suspension 23Na MR signal exhibited two T1 values, 9.1 (+/-0.3) ms and 32.7 (+/-2.3) ms, assigned to 23Nai+ and 23Nae+, respectively. The Nai+ content measured was lower, 0.88 (+/-0.06); while Nae+ was higher, 1.43 (+/-0.12) compared with MRS/SRe measures on the same samples. However, the measured efflux rate constant was identical. T1 MRR potentially may be used for Nai+ determination in vivo and Na+ flux measurements; with RRe for animal studies and without RRe for humans.
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Affiliation(s)
- Yajie Zhang
- Physiological NMR Core Laboratory, Division of Cardiovascular Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA
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Päuser S, Zschunke A, Khuen A, Keller K. Estimation of water content and water mobility in the nucleus and cytoplasm of Xenopus laevis oocytes by NMR microscopy. Magn Reson Imaging 1995; 13:269-76. [PMID: 7739369 DOI: 10.1016/0730-725x(94)00109-g] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
NMR microscopy is a noninvasive approach for studying cell structure and properties. Spatially resolved measurements of the relaxation times T1 and T2 provided information on the water proton spin density and water mobility in different parts of Xenopus laevis oocytes. The spin-lattice relaxation time T1 was determined using a saturation-recovery sequence and the common spin-echo sequence with increasing repetition times, while the transverse relaxation time T2 was measured by means of the spin-echo sequence with varying echo times. From the relaxation times, the mole fractions of possible reorientational correlation times tau c for different types of intracellular water were calculated according to a simple two-phase model. The values for T1, T2, and proton spin density (i.e., water content) are: nucleus >> animal cytoplasm > vegetal cytoplasm. Based on the estimation of tau c, nearly 90% of the nuclear water and 74.4% of the water of the animal pole was considered as free mobile water, whereas 55.5% of the water of the vegetal pole appeared as bound water.
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Affiliation(s)
- S Päuser
- Institut für Angewandte Analytik und Umweltchemie, Fachbereich Chemie der Humboldt-Universität zu Berlin, Germany
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Simor T, Kim SK, Chu WJ, Pohost GM, Elgavish GA. A selective inversion recovery method for the improvement of 23Na NMR spectral resolution in isolated perfused rat hearts. NMR IN BIOMEDICINE 1993; 6:201-208. [PMID: 8347454 DOI: 10.1002/nbm.1940060306] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Shift-reagent-aided 23Na NMR spectroscopy allows differentiation of the intracellular (Na(i)) and extracellular sodium (Na(o)) signals. The goal of the present study has been to develop a 23Na NMR spectroscopic method to minimize the intensity of the shift-reagent-shifted Na(o) signal and thus increase Na(i) resolution. This is achieved by a selective inversion recovery (SIR) method which enhances the resolution between the Na(i) and Na(o) peaks in shift-reagent-aided 23Na NMR spectroscopy. The application of SIR with Dy(TTHA), Tm(DOTP), or with low concentrations of Dy(PPP)2 results in both good spectral resolution and physiologically acceptable contractile function in the isolated, perfused rat heart model.
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Affiliation(s)
- T Simor
- Department of Medicine, University of Alabama, Birmingham 35294-0006
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Päuser S, Keller K, Zschunke A, Mügge C. Study of the membrane permeability of a paramagnetic metal complex on single cells by NMR microscopy. Magn Reson Imaging 1993; 11:419-24. [PMID: 8505875 DOI: 10.1016/0730-725x(93)90075-o] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
A new procedure has been developed for investigating the ability of paramagnetic metal complexes to penetrate the plasma membrane of eukaryotic cells without decomposition. Defolliculated Xenopus laevis oocytes formed the biological system to test N,N-ethylenebis-(1,5,5-trimethyltetramic-acid-3-acetiminato) copper (II). An increase of the signal intensities in spin-echo (SE) images of oocytes treated with the tested substance indicated that the complex was able to penetrate biological membranes due to the arrangement of hydrophobic and hydrophilic groups within the ligand. In contrast, the treatment with the commonly used contrast agent gadolinium-DTPA/dimeglumine did not enhance the signal intensity in NMR images of oocytes after time periods of exposure comparable to those used for the copper complex. After microinjection into Xenopus oocytes the copper complex was released into the extracellular medium without degradation, as shown by HPLC measurements.
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Affiliation(s)
- S Päuser
- Institute of Analytical Chemistry, Humboldt University of Berlin, Germany
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Kawano M, Ueno A, Ashida Y, Matsumoto N, Inoue H. Effects of sialagogues on ornithine decarboxylase induction and proto-oncogene expression in murine parotid gland. J Dent Res 1992; 71:1885-90. [PMID: 1452888 DOI: 10.1177/00220345920710120601] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The mechanism of a sialagogue-induced increase in ornithine decarboxylase (ODC) activity and the expressions of proto-oncogenes in murine parotid gland were investigated by use of isoproterenol (IPR), carbachol (CC), and methoxamine (MTX). The results were as follows: (1) The three sialagogues had similar effects on the parotid in vivo (mouse parotid after a single injection of IPR) and/or in vitro (rat parotid explants cultured on siliconized lens paper floating on 199 medium containing IPR, CC, or MTX), the order of their effectiveness being IPR > CC > MTX. (2) Northern/dot and Western blot analyses revealed that the sialagogues elevated the steady-state levels of ODC mRNA and ODC protein to maxima at two h and six h, respectively, after stimulation. The increases were roughly proportional to those in ODC activity, suggesting that sialagogue-dependent enzyme induction is regulated at the transcriptional level. (3) The mRNAs of four of nine proto-oncogenes examined showed sialagogue-dependent increases to maxima at 30 min (c-fos) or 60 min (c-jun, c-myc, and c-src) after the beginning of stimulation. These increases were all transient, with the levels returning to the control values (without sialagogue) within 60 min. (4) The IPR-dependent elevations of ODC activity and the mRNAs of ODC, c-fos, and c-jun were inhibited by monensin, but not by polymyxin B. On the other hand, the CC-dependent increases in these parameters were inhibited by polymyxin B but not by monensin.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M Kawano
- Department of Biochemistry, School of Dentistry, University of Tokushima, Japan
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Shift-Reagent-Aided 23Na NMR Spectroscopy in Cellular, Tissue, and Whole-Organ Systems. ACTA ACUST UNITED AC 1992. [DOI: 10.1007/978-1-4757-9477-9_4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Miller SK, Chu WJ, Pohost GM, Elgavish GA. Improvement of spectral resolution in shift-reagent-aided 23Na NMR spectroscopy in the isolated perfused rat heart system. Magn Reson Med 1991; 20:184-95. [PMID: 1775046 DOI: 10.1002/mrm.1910200203] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The level of intracellular sodium (Nai) is maintained at approximately 14 mM in healthy myocytes. When myocytes are damaged, Nai increases and therefore the level of Nai may be a means of evaluating myocardial cell integrity. A particularly useful method to monitor Nai levels is 23Na NMR spectroscopy. However, because of the isochronous nature of the extracellular sodium (Nao) and Nai NMR signals, paramagnetic lanthanide shift reagents (LSR), such as dysprosium triphosphate, Dy(PPP)7-(2), have been used to shift the Nao signal. This reveals the unshifted Nai signal and allows the NMR monitoring of Nai in isolated perfused hearts and other systems. A major shortcoming of this method (the "shift-only" method) is in the need to minimize the Nao signal by not submerging the perfused hearts in Na(+)-containing buffer. An equally undesirable alternative is the utilization of relatively high concentrations of LSR to shift a large Nao signal sufficiently to enable reasonable resolution and quantitation of Nai. We present here a method, the "shift-relaxation" method, which is a combination of using a mixture of Dy(PPP)7-(2), a shift reagent, and gadolinium triphosphate, Gd(PPP)7-(2), a relaxation agent, with data acquisition using an inversion-recovery (IR) pulse sequence. This combination allows differentiation between Nao and Nai by the difference in their respective T1 values in addition to the shift between them. With this technique we can selectively minimize the extracellular signal and therefore minimize the need for a large Dy-induced shift, as well as allow data acquisition on a heart submerged in Na(+)-containing perfusate. The resulting improved discrimination between Nai and Nao at relatively low levels of LSR should be helpful for ultimate in vivo applications and potential clinical applications, where a lower dose of LSR also means a decreased possibility of physiologically deleterious effects. Also included in this paper is a method for the quick determination of an accurate 180 degrees pulse which is required for the optimization of the IR method.
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Affiliation(s)
- S K Miller
- Department of Medicine, University of Alabama, Birmingham 35294
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Nissen H, Jacobsen JP, Hørder M. A review of 23Na nuclear magnetic resonance spectroscopy for the in vitro study of cellular sodium metabolism. Scand J Clin Lab Invest 1990; 50:497-507. [PMID: 2237262 DOI: 10.1080/00365519009089164] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Changes in intracellular sodium have been associated with a number of different diseases. Consequently, various methods have been used to quantify the level of intracellular sodium concentrations. Traditional methods like flame photometry and ion-selective electrodes are destructive or invasive, thereby potentially altering the intracellular sodium levels. There has been an increasing interest in evaluating the method of 23Na nuclear magnetic resonance in recent years, since this method allows for non-invasive continuous monitoring of intracellular sodium in cell suspensions and tissues. A phenomenological approach to basic theory, review of methodology, applications to the in vitro study of cellular sodium metabolism, and difficulties of interpretation of this analytical modality is presented.
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Affiliation(s)
- H Nissen
- Department of Clinical Chemistry, Odense University Hospital, Denmark
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Knubovets TL, Revazov AV, Sibeldina LA, Eichhoff U. 23Na NMR measurement of the maximal rate of active sodium efflux from human red blood cells. Magn Reson Med 1989; 9:261-72. [PMID: 2541305 DOI: 10.1002/mrm.1910090211] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The method for 23Na NMR measurement of the maximal rate of active Na+ efflux from human red blood cells (RBC) is proposed. The nonpenetrating paramagnetic shift reagent (SR) bis(tripolyphosphate)dysprosium(III) complex is used to distinguish extracellular Na+ ions from intracellular. RBC are proved to retain their physiological activity in the presence of SR. Intracellular Na+ is shown to be 100% NMR visible. The levels of intracellular and extracellular Na+ and K+ ions are changed to decrease their concentration gradients across the erythrocyte membrane to make active Na+ efflux the only 23Na NMR measurable process; so the integrated areas of intra- and extracellular Na+ peaks remain invariant throughout the incubation period in the presence of 0.25 mM ouabain, a specific inhibitor of Na+, K+-ATPase. The accuracy of the proposed technique is evaluated to be 10%. The maximal Na+ efflux is determined to be 10.1 +/- 1.0 mM/h/liter of cells.
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Affiliation(s)
- T L Knubovets
- Institute of Chemical Physics, Academy of Science USSR, Moscow
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Civan MM, Shporer M. Chapter 1 Physical State of Cell Sodium. CURRENT TOPICS IN MEMBRANES AND TRANSPORT 1989. [DOI: 10.1016/s0070-2161(08)60005-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Lohman JA, Ratcliffe RG. Prospects for NMR imaging in the study of biological morphogenesis. EXPERIENTIA 1988; 44:666-72. [PMID: 3409998 DOI: 10.1007/bf01941027] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Small objects can be visualised with a spatial resolution that approaches microscopic dimensions using the technique of high resolution nuclear magnetic resonance (NMR) imaging. Some important features of the method are described and the prospects for using the technique to study morphogenesis are discussed. It is concluded that NMR imaging, in conjunction with the related method of localised spectroscopy, is capable of producing novel structural information.
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Affiliation(s)
- J A Lohman
- Oxford Research Systems Limited, Abingdon, Oxon, England
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Sherry A, Malloy CR, Jeffrey FH, Cacheris WP, Geraldes CF. Dy(DOTP)5−: A new, stable 23Na shift reagent. ACTA ACUST UNITED AC 1988. [DOI: 10.1016/0022-2364(88)90354-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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A 31P and 23Na NMR and terbium(III) luminescence study of bistriphosphato-lanthanide(III) complexes including the cation shift reagent [Dy(PPP)2]7−. Inorganica Chim Acta 1987. [DOI: 10.1016/s0020-1693(00)81227-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Liebling MS, Gupta RK. A comparison of intracellular sodium ion concentrations in neoplastic and nonneoplastic human tissue using 23Na NMR spectroscopy. Ann N Y Acad Sci 1987; 508:149-63. [PMID: 3439700 DOI: 10.1111/j.1749-6632.1987.tb32901.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- M S Liebling
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, Yeshiva University, New York, New York 10461
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Martin JB, Klein G, Satre M. 23Na NMR study of intracellular sodium ions in Dictyostelium discoideum amoeba. Arch Biochem Biophys 1987; 254:559-67. [PMID: 3579318 DOI: 10.1016/0003-9861(87)90138-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The intracellular sodium concentration in the amoebae from the slime mold Dictyostelium discoideum has been studied using 23Na NMR. The 23Na resonances from intracellular and extracellular compartments could be observed separately in the presence of the anionic shift reagent Dy(PPPi)7-2 which does not enter into the amoebae and thus selectively affects Na+ in the extracellular space. 31P NMR was used to control the absence of cellular toxicity of the shift reagent. The intracellular Na+ content was calculated by comparison of the intensities of the two distinct peaks arising from the intra- and extracellular spaces. It remained low (0.6 to 3 mM) in the presence of external Na+ (20 to 70 mM), and a large Na+ gradient (20- to 40-fold) was maintained. A rapid reloading of cells previously depleted of Na+ was readily measured by 23Na NMR. Nystatin, an antibiotic known to perturb the ion permeability of membranes, increased the intracellular Na+ concentration. The time dependence of the 23Na and 31P NMR spectra showed a rapid degradation of Dy(PPPi)7-2 which may be catalyzed by an acid phosphatase.
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