23Na NMR shift reagents enhance cardiac staircase effect in isolated perfused rat hearts

Intracellular Sodium Changes in Cancer Cells Using a Microcavity Array-Based Bioreactor System and Sodium Triple-Quantum MR Signal

The sodium triple-quantum (TQ) magnetic resonance (MR) signal created by interactions of sodium ions with macromolecules has been demonstrated to be a valuable biomarker for cell viability. The aim of this study was to monitor a cellular response using the sodium TQ signal during inhibition of Na/K-ATPase in living cancer cells (HepG2). The cells were dynamically investigated after exposure to 1 mM ouabain or K+-free medium for 60 min using an MR-compatible bioreactor system. An improved TQ time proportional phase incrementation (TQTPPI) pulse sequence with almost four times TQ signal-to-noise ratio (SNR) gain allowed for conducting experiments with 12–14 × 106 cells using a 9.4 T MR scanner. During cell intervention experiments, the sodium TQ signal increased to 138.9 ± 4.1% and 183.4 ± 8.9% for 1 mM ouabain (n = 3) and K+-free medium (n = 3), respectively. During reperfusion with normal medium, the sodium TQ signal further increased to 169.2 ± 5.3% for the ouabain experiment, while it recovered to 128.5 ± 6.8% for the K+-free experiment. These sodium TQ signal increases agree with an influx of sodium ions during Na/K-ATPase inhibition and hence a reduced cell viability. The improved TQ signal detection combined with this MR-compatible bioreactor system provides a capability to investigate the cellular response of a variety of cells using the sodium TQ MR signal.

Multiple quantum filtered (23)Na NMR in the Langendorff perfused mouse heart: Ratio of triple/double quantum filtered signals correlates with [Na]i

We investigate the potential of multiple quantum filtered (MQF) ²³Na NMR to probe intracellular [Na]_i in the Langendorff perfused mouse heart. In the presence of Tm(DOTP) shift reagent the triple quantum filtered (TQF) signal originated largely from the intracellular sodium pool with a 32 ± 6% contribution of the total TQF signal arising from extracellular sodium, whilst the rank 2 double-quantum filtered signal (DQF), acquired with a 54.7° flip-angle pulse, originated exclusively from the extracellular sodium pool. Given the different cellular origins of the ²³Na MQF signals we propose that the TQF/DQF ratio can be used as a semi-quantitative measure of [Na]_i in the mouse heart. We demonstrate a good correlation of this ratio with [Na]_i measured with shift reagent at baseline and under conditions of elevated [Na]_i. We compare the measurements of [Na]_i using both shift reagent and TQF/DQF ratio in a cohort of wild type mouse hearts and in a transgenic PLM^3SA mouse expressing a non-phosphorylatable form of phospholemman, showing a modest but measurable elevation of baseline [Na]_i. MQF filtered ²³Na NMR is a potentially useful tool for studying normal and pathophysiological changes in [Na]_i, particularly in transgenic mouse models with altered Na regulation.

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Intracellular Na concentration [Na]_i is a key modulator of cardiac cell function.

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We developed an NMR-compatible Langendorff mouse heart perfusion system.

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The ratio of triple/double quantum filtered ²³Na NMR signals correlates with [Na]_i.

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Intracellular [Na]_i can be quantified under physiological perfusion conditions.

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The PLM^3SA transgenic mouse model has a measurable elevation of [Na]_i at baseline.

23Na NMR study of Fibrobacter succinogenes S85: comparison of three chemical shift reagents and calculation of sodium concentration using ionophores

In order to measure intracellular sodium concentrations in resting cells of Fibrobacter succinogenes S85 by (23)Na NMR spectrometry, two methodological aspects were studied. First, three different shift reagents (Dy(PPP(i))(7-)(2), Tm(DOTP)(5-), and Dy(TTHA)(3-)) were tested for their ability to separate internal and external (23)Na NMR resonances. Their toxicity toward F. succinogenes cells was evaluated by in vivo(13)C NMR experiments. Tm(DOTP)(5-) was found to be the most efficient shift reagent while being nontoxic. Second, a new methodology was developed to calculate intracellular sodium concentration in F. succinogenes by using ionophores. This approach avoided the problem of intracellular volume measurement and that of sodium visibility determination.

Synthesis and NMR studies of new DOTP-like lanthanide(III) complexes containing a hydrophobic substituent on one phosphonate side arm

Three derivatives of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylene phosphonic acid) (DOTP) containing a hydrophobic substituent on one side chain were prepared and their lanthanide complexes examined by NMR. The new ligands include 1-(1-octyl-methyl-phosphonic acid)-4,7,10-tris(methylene phosphonic acid)-1,4,7,10-tetraazacyclododecane (C(8)-DOTP), 1-(1-undecyl-methyl-phosphonic acid)-4,7,10-tris(methylene phosphonic acid)-1,4,7,10-tetraazacyclododecane (C(11)-DOTP), and 1-(1-4-nitro-phenyl-methyl-phosphonic acid)-4,7,10-tris(methylene phosphonic acid)-1,4,7,10-tetraazacyclododecane (NO(2)-Ph-DOTP). (1)H NMR spectra of the ytterbium(III) complexes were assigned by using a combination of COSY spectroscopy and a fitting procedure that matches experimental NMR hyperfine shifts with those estimated from a MMX-derived structure. The analysis showed that a single isomer is present in solution and that the bulky hydrophobic substituent occupies the less sterically demanding H(6) equatorial position in the YbL(5)(-) complexes. Although the YbL(5)(-) complexes have lower symmetry due to the added substituent, the average (1)H hyperfine shifts are 5-10% larger in these complexes compared to YbDOTP(5)(-). This was magnified further in the hyperfine (23)Na NMR shifts of ion-paired sodium ions where the extracellular Na(+) signal in perfused rat hearts displayed a 28% larger hyperfine shift in the presence of Tm(C(11)-DOTP)(5)(-) than with an equivalent amount of TmDOTP(5)(-).