DOUBLE-QUANTUM-FILTERED NA-23 NMR-STUDY OF INTRACELLULAR SODIUM IN THE PERFUSED LIVER

We acquired double-quantum-filtered Na-23 NMR spectra from perfused liver, using a range of tau values from 0.2 to 24 ms, where tau is the separation between the first and second pi/2 pulses in the radio-frequency pulse sequence. For each tau value we compared the amplitude of the double-quantum-filtered Na-23 NMR signal acquired from intracellular sodium ions when the liver was perfused with buffer containing the ''shift reagent'' Dy(PPP)(2) to the amplitude of the total double-quantum-filtered Na-23 NMR signal acquired when the liver was perfused with buffer containing no Dy(PPP)(2). For tau less than or equal to( )4 ms, the average ratio of the two amplitudes was 0.98 +/- 0.03 (mean +/- SEM). For tau less than or equal to 8 ms, the average ratio was significantly less than 1. These results demonstrate that double-quantum-filtered Na-23 NMR signals acquired from perfused liver using short tau values arise almost exclusively from intracellular sodium ions, but double-quantum-filtered Na-23 NMR signals acquired from perfused liver using long tau values contain contributions from both intracellular and extracellular sodium ions. This conclusion suggests that multiple-quantum-filtered Na-23 NMR spectroscopy will be useful in studying intracellular sodium levels in the perfused liver, and possibly in the intact liver in vivo.