Determination of the intracellular sodium concentration in perfused mouse liver by 31 P and 23 Na magnetic resonance spectroscopy

A combination of 31 P and 23 Na NMR spectroscopy has been used to quantify the concentration of intracellular sodium, [Na] IC in the isolated and perfused mouse liver. The 31 P resonances of dimethyl methylphosphonate and LaDOTP 5− , markers of total tissue space and extracellular space, respectively, were used to determine the intracellular liver volume. For a mean wet weight of 1.7 ± 0.3 g, the intracellular liver volume as measured by 31 P NMR averaged 1.2 ± 0.2 ml. The amount of intracellular sodium was measured from the baseline‐resolved intracellular 23 Na resonance during perfusion of the shift reagent, TmDOTP 5− . These two measurements resulted in an NMR‐determined value for [Na] IC of 29.0 ± 5.2 mM. Separate measurement of total tissue Tm and Na by atomic absorption spectroscopy on the same samples provided an AAS‐determined value for [Na] Ic of 32.1 ± 7.4 mM . These results indicate that intracellular sodium in the isolated, perfused liver is 100% visible by 23 Na NMR spectroscopy.