The State of Water in Polarized and Depolarized Frog Nerves: A Proton Magnetic Resonance Study

The high resolution proton magnetic resonance spectrum of the sciatic nerve of the frog was studied in both the polarized and depolarized states. Paramagnetic salts were introduced into the system in order to separate the signals from the intra- and extracellular environments. It was determined that about 65% of the proton signal from the nerve trunk was accounted for by the intracellular environment in the polarized nerve trunk and that this percentage decreased to about 34% in the depolarized case.

The temperature dependence of the line widths of the intracellular proton signal was studied. The enthalpy and entropy of activation for proton exchange between the intra- and extracellular environments were found to be 11.1 kcal/mole and -17.1 cal/deg-mole respectively. The pseudo-first-order rate constant for proton exchange between the intra- and extracellular environments was determined at 20°C and shown to agree with the measured permeability coefficients of similar cells.

Data are presented which indicate that the pseudo-first order rate constant for proton exchange between the two environments decreases upon depolarization of the nerve trunk and that the proton spin-spin relaxation time of the protons of intracellular water decreases significantly with depolarization.

These results indicate a possibly quite important role of water in neural phenomena.