Multiple quantum filtered23Na NMR spectroscopy of the isolated, perfused rat liver

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Abstract
Isolated, perfused rat livers were examined by single-quantum (SQ) and double-quantum-filtered (DQ-filtered) 23Na spectroscopy during prolonged global ischemia and during perfusion with ouabain, low-buffer potassium, or lithium-enriched buffer. Baseline separation of the intracellular (Nai+) and extracellular (Nae+) sodium resonances using TmDOTP5- allowed a direct comparison of temporal changes in SQ versus DQ-filtered Nai+. The SQ Nai+ signal increased ∼150% during the first 15 min of global ischemia and then remained relatively constant over the next 45 min, while the DQ-filtered signal steadily increased ∼400% over the same 60 min period. In similar experiments in which all perfusate sodium was replaced by lithium, the DQ-filtered Nai+ signal increased ∼180% over a similar period of ischemia. Exposure of livers to ouabain also resulted in larger increases in DQ-filtered versus SQ signal of Nai+. The ∼290% increase in DQ-filtered sodium observed during perfusion of livers with a hypokalemic buffer (1.2 mM K+) could be completely reversed by continued perfusion with a buffer containing normal levels of K+ (4.7 mM). These data suggest that the DQ-filtered Nai+ signal of liver does not simply report an increase in [Nai+], but may be exquisitely sensitive to other intracellular events initiated by altered physiology. Magn Reson Med 41:1127–1135, 1999.

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