Discriminative Detection of Extracellular and Intracellular Sodium in Nerve Fibers by Magnetic Resonance Spectroscopy

The present study demonstrated the measurement of Na
_e
/ Na
_i
in sciatic nerves by
²³
Na-MRS using
²³
Na frequency shift agent Na
₄
HTmDOTP. Sciatic nerves from bull frogs were submerged into the 5 mM TmDOTP solution for 12 h before acquisition. MRS was performed on a Varian 4.7-T magnetic resonance spectrometer. To obtain the shift of Na
_e
/ Na
_i
resonance,
²³
Na spectra were acquired from the whole sample with TR 50 ms and 800 averages. Na
_e
and Na
_i
signals were detected clearly in the spectra of TmDOTP solution-immerged nerve. Then, for evaluation of nerves viability, action potential of TmDOTP solution-immerged nerve was examined. TmDOTP had no effects on the generation of action potential. An increase of Na
_e
signal/Na
_i
signal was observed during the electrical stimulation, suggesting that this result reflected the direct changes in sodium ions permeability during the nerves excitation.