Spin-Echo Nuclear Magnetic Resonance Evidence for Complexing of Sodium Ions in Muscle, Brain, and Kidney

Na+ in muscle, brain, and kidney is shown by spin-echo nuclear magnetic resonance (NMR) to consist of two fractions with different NMR parameters. The slow fraction of Na+ in these tissues has NMR relaxation times T1 and T2 of 10–15×10-3 sec, which is approximately 4–5 times shorter than for Na+ in aqueous NaCl solution. The slow fraction may represent Na+ dissolved in structured tissue water. The fast fraction of tissue Na+, which is shown to represent approximately 65% of the total tissue Na+ concentration, has T2 less than 1×10-3 sec, which resembles the values of T2 observed for Na+ complexed by synthetic ion-exchange resins. One is drawn to the conclusion that approximately 65% of total Na+ in muscle, brain, and kidney is complexed by tissue macromolecules