Abstract: The feasibility of employing triple-quantum-filtered (TQF) or double-quantum-filtered (DQF)23Na NMR spectra to monitor intracellular Na (Nain) content in isolated rat hearts perfused in the absence of a chemical-shift reagent (SR) was investigated. This necessitated characterization of the following: first, the pool of Nainrepresented by the intracellular TQF (TQFin) spectrum; second, the maximum extent to which altered transverse relaxation times affect TQFinspectral amplitudes; and finally, the situations for which the SR-free method can reliably be applied. The rates of increase in peak amplitudes of both intracellular TQF spectra, adjusted for changes in both fast (T2f) and slow (T2s) transverse relaxation times, and intracellular single-quantum (SQin) spectra were identical during no-flow ischemia, indicating that TQFinand SQinspectra represent the same Nainpopulation. Addition of an Na/K ATPase inhibitor, ouabain (≥500 μM), and no-flow ischemia induced similar rates of increase of Naincontent. However, the Nainlevel for which theT2values started to increase was lower for ischemic (<140% of preischemic values) than for ouabain-exposed (>165%) hearts, which is consistent with the known earlier onset of intracellular swelling in ischemic hearts. Exposure of hearts to hyperosmotic perfusate (200 mMsucrose) increased [Nain], due to a decreased cell volume and an unchanged Naincontent, but caused a decrease inT2values, a trend opposite to that observed with exposure of hearts to ouabain or ischemia.T2values therefore consistently correlated only with cell volume, not with Naincontent or concentration, indicating an important role for intracellular macromolecule concentration in modulating transverse relaxation behavior. The combined effect of ischemia-induced increases inT2values and their inhomogeneous broadened forms was an ∼6% overestimation of Naincontent from amplitudes of SR-aided TQFinspectra, indicating negligible effect of transverse relaxation-dependent alterations on TQFinspectral amplitudes. Thus, Naincontent may be reliably determined from SR-free TQF spectra when the contribution from extracellular Na does not appreciably vary, such as during constant pressure perfusion. Following complete reduction in perfusion pressure, both SR-free TQF and DQF spectra respond to increases in Naincontent. However, SR-free DQF NMR provides an estimate of Naincontent much closer to that provided by the SR-aided method, due to the appreciable decrease of the extracellular DQF signal resulting from destructive interference between second- and third-rank tensors.

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{{Explor lien
   |wiki=    Wicri/Terre
   |area=    ThuliumV1
   |flux=    Main
   |étape=   Merge
   |type=    RBID
   |clé=     ISTEX:3C05A9E93E0F1B48AB7295845D12804B6E2E007D
   |texte=   Evaluation of Multiple-Quantum-Filtered23Na NMR in Monitoring Intracellular Na Content in the Isolated Perfused Rat Heart in the Absence of a Chemical-Shift Reagent
}}