Quantitation of intracellular [Na+] in vivo by using TmDOTP5-asanNMRshiftreagentand extracellularmarker

A method ispresented to measure the absolute concentration of intracellularNa⁺(Na⁺]_i)in vivo by using interleaved ²³Na-and ³¹P-nuclear magnetic resonance(NMR) spectroscopy andTmDOTP⁵ as shift reagentand chemical marker of tissue extracellular space (ECS). The techniquewas used to determineNa⁺]_iand relative ECS in livers of control rats (21 ± 3 and0.11 ± 0.02 mM, respectively) and in rats exposed to carbontetrachloride (103 ± 29 and 0.23 ± 0.03 mM, respectively). TheNMR measurements were confirmed independently on excised tissue samplesby using atomic absorption spectroscopy. The results confirm thatTmDOTP⁵ can be used as acombined cation shift reagent and ECS marker, thereby allowingquantitation ofNa⁺]_iin vivo by NMR.