EVALUATION OF TRIPLE-QUANTUM-FILTERED NA-23 NMR IN MONITORING OF INTRACELLULAR NA CONTENT IN THE PERFUSED RAT-HEART - COMPARISON OF INTRACELLULAR AND EXTRACELLULAR TRANSVERSE RELAXATION AND SPECTRAL AMPLITUDES

Multiple-quantum filtered (MQF) NMR offers the possibility of monitori ng intracellular (IC) Na content in the absence of shift reagents (SR) , provided that (i) the contribution from IC Na to the MQF spectrum is substantial and responds to a change in IC Na content, and (ii) the a mplitude of the extracellular (EC) MQF component remains constant duri ng a change in IC Na content, The validity and basis for these conditi ons were examined in isolated perfused rat hearts using SR-aided and S R-free triple-quantum filtered (TQF) (23)NaNMR, Despite a myocardial N a content that was only similar to 1/70 that of EC Na, IC Na contribut ed to over 25% of the total TQF spectrum acquired in the absence of SR , Transverse relaxation times (T-2) were approximately twice as long f or EC compared to IC Na, despite SR-induced relaxation of T-2 for the former pool, However, the efficiency of generation of the TQF signal w as similar for IC and EC Na, indicating that a much greater percentage of IC relative to EC Na exhibits TQ coherence, During constant perfus ion with ouabain (0.2 mM for 25 min) or with a hypoxic and aglycemic s olution (50 min), the amplitude of the IC TQF spectrum increased by si milar to 330% and -280%, respectively. In contrast, the amplitude of t he EC TQF spectra remained essentially constant for both interventions , The amplitude for IC Na increased similar to 250% relative to baseli ne during no-flow ischemia (60 min), whereas the amplitude of the EC T QF spectra decreased by similar to 33% before stabilizing, In SR-free experiments, the TQF spectral amplitude increased similar to 2-fold du ring the constant perfusion interventions, but did not change signific antly during no-flow ischemia, These data suggest that the change in t he TQF spectral amplitude during constant perfusion interventions is f rom IC Na, and that TQF techniques in the absence of SR may be useful in monitoring IC Na during these interventions, The fall in the amplit ude of the EC TQF spectral amplitude during no-flow ischemia complicat es the use of TQF techniques without SR during this intervention.