NMR monitoring of intracellular sodium in dog and rabbit kidney-tubules

Abstract

23Na-nuclear magnetic resonance (NMR) was used to monitor intra- and extracellular sodium in suspensions of dog cortical tubules, rabbit cortical tubules, and dog thick ascending limbs. The NMR visibility of the intracellular sodium was determined by comparing the NMR and flame photometry results and by redistributing the sodium ions between the intra- and extracellular compartments using the ionophore nystatin (influx) or sodium substitution for choline in the extracellular fluid (efflux). The intracellular sodium visibility was approximately 30% for the total sodium and 58% for the transportable sodium. Addition of sodium to sodium-depleted homogenates of dog renal cortex also showed a loss of visibility. The values of the relaxation times T1 and T2 were determined but could not be correlated with the visibility measurements. The intracellular sodium concentration in dog cortical tubules incubated in optimal biochemical conditions was estimated at 51 mM and was dependent on the extracellular sodium concentration.