23Na nuclear magnetic resonance studies of ion transport in the rabbit proximal tubule

23Na nuclear magnetic resonance (n.m.r.) spectroscopy was used to measure intracellular sodium levels in suspensions of rabbit proximal tubules. The intracellular sodium signal was resolved by incorporating the paramagnetic shift reagent dysprosium tripolyphosphate into the suspension buffers. This shift reagent was membrane impermeant, and induced a large upfield shift of the n.m.r. signal from the extracellular sodium pool, while leaving the intracellular pool unshifted. Tubule viability and transport characteristics were unimpaired in the presence of the shift reagent provided there was no excess tripolyphosphate, and extra calcium was added to the buffer