Cesium uptake studies on human erythrocytes

In-cell NMR: Why and how?

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.

Highly selective and sensitive simultaneous nanomolar detection of Cs(i) and Al(iii) ions using tripodal organic nanoparticles in aqueous media: the effect of the urea backbone on chemosensing

Chemosensing plays a very important role in the detection of essential/pollutant ions in aqueous media. In this manuscript, two tripodal ligands, i.e., 1-(2-hydroxybenzyl)-3-(4-nitrophenyl)-1-phenylurea (ligand 1) and 1-(2-hydroxybenzyl)-3-(4-nitrophenyl)-1-phenylthiourea (ligand 2) have been synthesised, which differ in the linker molecule, i.e., urea and thiourea in ligand 1 and ligand 2, respectively. The ligands were characterised by NMR, IR and mass spectroscopic techniques. Ligands 1 and 2 (2 mM) were further employed for the generation of their organic nanoparticles (ONPs) (0.01 mM) of size 20–25 nm and 30–35 nm, respectively, by the reprecipitation method. The chemosensing properties of 1-ONP and 2-ONP solutions were investigated. 1-ONP showed simultaneous recognition behaviour towards Cs(i) and Al(iii) with the limits of detection of ∼220 and ∼377 nM, respectively, in an aqueous medium, while 2-ONP did not show any recognition behaviour towards any ion.

Two ligands 1 and 2 are synthesized and their organic nanoparticles (1-ONP and 2-ONP) are generated. 1-ONP has shown the chemosensing of Cs(i) (∼220 nm) and Al(iii) (∼377 nm) in aqueous medium while 2-ONP has not shown any chemosensing behaviour.

Biomedical applications of 133Cs NMR

133Cs NMR is a valuable tool for non-invasively probing biological systems. As a congener of potassium, it accumulates in the intracellular space, primarily through the action of the Na+-K+ pump (ATPase). In addition, it is possible to resolve the MR signal of 133Cs in different tissue compartments on the basis of chemical shift or MR relaxation properties. This compartmental resolution applies not only to the intra- and extracellular spaces, but to subcellular compartments as well. In this review, we discuss the studies defining the ion transport, chemical shift and relaxation characteristics of 133Cs in living systems. We also review the application of 133Cs NMR to evaluation of ion transport across membranes and the kinetic/chemical environment of the intracellular space in systems ranging from red blood cells to rat brain.

Nuclear magnetic resonance and oxygen affinity study of cesium binding in human erythrocytes

We investigated the interaction of the cesium ion (Cs(+)) with the anionic intracellular components of human red blood cells (RBCs); the components studied included 2,3-bisphosphoglycerate (BPG), ADP, ATP, inorganic phosphate (P(i)), carbonmonoxy hemoglobin (COHb), and RBC membranes. We used spin-lattice (T(1)) and spin-spin (T(2)) (133)Cs NMR relaxation measurements to probe Cs(+) binding, and we found that Cs(+) bound more strongly to binding sites in BPG and in RBC membranes than in any other intracellular component in RBCs at physiologic concentrations. By using James-Noggle plots, we obtained Cs(+) binding constants per binding site in BPG (66 +/- 8 M(-1)), ADP (19 +/- 1 M(-1)), ATP (25 +/- 3 M(-1)), and RBC membranes (55 +/- 2 M(-1)) from the observed T(1) values. We also studied the effect of Cs(+) on the oxygen (O(2)) affinity of purified Hb and of Hb in intact RBCs in the absence and in the presence of BPG. In the absence of BPG, the O(2) affinity of Hb decreased upon addition of Cs(+). However, in the presence of BPG, the O(2) affinity of Hb increased upon addition of Cs(+). The O(2) affinity of Cs(+)-loaded human RBCs was larger than that of Cs(+)-free cells at the same BPG level. (31)P NMR studies on the pH dependence of the interaction between BPG and Hb indicated that the presence of Cs(+) resulted in a smaller fraction of BPG available to bind to the cleft of deoxyHb. Our NMR and O(2) affinity data indicate that a strong binding site for Cs(+) in human RBCs is BPG. A partial mechanism for Cs(+) toxicity might arise from competition between Cs(+) and deoxyHb for BPG, thereby increasing oxygenation of Hb in RBCs, and thus decreasing the ability of RBCs to give up oxygen in tissues. The presence of Cs(+) at 12.5 mM in intact human RBCs containing BPG at normal concentrations did not, however, alter significantly the O(2) affinity of Hb, thus ruling out the possibility of Cs(+)-BPG interactions accounting for Cs(+) toxicity in this cell type.

Nuclear magnetic resonance studies of cesium-133 in the halophilic halotolerant bacterium Ba1. Chemical shift and transport studies

Ba1 bacteria (Halomonas israelensis) were grown on different salt concentrations 0.2-4 M. When the cells were transferred to a medium containing 25 mM CsCl without potassium there was an uptake of cesium by the cells. The intracellular cesium signal was shifted from the cesium signal in the medium without the use of a shift reagent. The shift was depended on the salt concentration in the growth medium. The intracellular cesium shift showed a much smaller dependence on the concentration of salts in the medium than the extracellular cesium; the same results were detected for cells grown on a medium containing 25 mM CsCl. The cesium transport through the cell membrane was mostly by active transport. The cesium concentration in the cell was higher than that of the medium, approximately 100 mM intracellular concentration compared to 25 mM in the medium. The first order constants for influx or efflux of cesium were from 2 x 10(-4) and up to 24 x 10(-4)/min for the different medium concentrations.