Evaluation of extra- and intracellular apparent diffusion coefficient of sodium in rat skeletal muscle: Effects of prolonged ischemia

The mechanism of water and sodium apparent diffusion coefficient (ADC) changes in rat skeletal muscle during global ischemia was examined by in vivo H-1 and Na-23 magnetic resonance spectroscopy (MRS). The ADCs of Na+ and water are expected to have similar characteristics because sodium is present as an aqua-cation in tissue. The shift reagent, TmDOTP5-, was used to separate intra- and extracellular sodium (Na-i(+) and Na-e(+), respectively) signals. Water, total tissue sodium (Na-t(+), Na-i(+), and Na+, ADCs were measured before and 1, 2, 3, and 4 hr after ischemia. Contrary to the general perception, Na-i(+) and Na-e(+) ADCs were identical before ischemia. Thus, ischemia-induced changes in Na-t(+) ADC cannot be explained by a simple change in the size of relative intracellular or extracellular space. Na-t(+) and Na-e(+) ADCs decreased after 2-4 hr of ischemia, while water and Na-i(+) ADC remained unchanged. The correlation between Na-t(+) and Na-e(+) ADCs was observed because of high Na+, concentration. Similarly, the correlation between water and Na+, ADCs was observed because cells occupy 80% of the tissue space in the skeletal muscle. Ischernia also caused an increase in the Na-i(+) and an equal decrease in Na-e(+) signal intensity due to cessation of Na+/K+-ATPase function.