Assessment of the sensitivity of DQF/ZQF 2H NMR of D2O for studying modified nafion membranes at 20 °C and 80 °C

Double and zero quantum filtered (ZQF/DQF) ²H NMR spectroscopy was used to study D₂O in five different Nafion membranes, N117, N115, NR212, XL, and HP, in order to assess the effectiveness of the technique for monitoring differences in thickness, membrane reinforcement, and the addition of chemical stabilizers. Experiments were also carried out at 20 and 80 °C to understand if the ZQF/DQF technique could detect changes in the water environments and exchange dynamics as a function of temperature. For two of the membranes, significant decreases in the 1/T₂ relaxation rates were observed at 80 °C. The two modified membranes showed changes in the quadrupolar couplings when heated, with the XL membranes showing a drop in the coupling and the HP membranes showing an increase in the coupling. No consistent variations could be associated with thickness, reinforcement or the addition of stabilizers. Overall the technique was able to detect some differences between the membranes but was limited by the variability in the observed NMR data.

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.