Multiple quantum filtered Na-23 NMR spectroscopy of the isolated, perfusedrat liver

Isolated, perfused rat livers were examined by single-quantum (SQ) and doub le-quantum-filtered (DQ-filtered) Na-23 spectroscopy during prolonged globa l ischemia and during perfusion with ouabain, low-buffer potassium, or lith ium-enriched buffer. Baseline separation of the intracellular (Na-i(+)) and extracellular (Na-e(+)) sodium resonances using TmDOTP5- allowed a direct comparison of temporal changes in So versus Do-filtered Na-i(+). The SQ Na- i(+) signal increased similar to 150% during the first 15 min of global isc hemia and then remained relatively constant over the next 45 min, while the Do-filtered signal steadily increased similar to 400% over the same 60 min period. In similar experiments in which all perfusate sodium was replaced by lithium, the DQ-filtered Na-i(+) signal increased similar to 180% over a similar period of ischemia. Exposure of livers to ouabain also resulted in larger increases in Do-filtered versus so signal of Na-i(+). The similar t o 290% increase in Do-filtered sodium observed during perfusion of livers w ith a hypokalemic buffer (1.2 mM K+) could be completely reversed by contin ued perfusion with a buffer containing normal levels of K+ (4.7 mM). These data suggest that the Do-filtered Na-i(+) signal of liver does not simply r eport an increase in [Na-i (+)], but may be exquisitely sensitive to other intracellular events initiated by altered physiology. (C) 1999 Wiley-Liss, Inc.