23Na nuclear magnetic resonance study of intracellular sodium in vascular endothelial cells

Abstract

23Na +-NMR was used to determine the intracellular mobility and cell membrane permeability of Na + in porcine vascular endothelial cells. The cells were grown as monolayers onto microcarrier beads and perfused with a medium containing Dy(P 3O 10) 7− 2 to shift the extracellular from the intracellular Na + resonance. Using triple quantum coherence filtered NMR experiments and spin echoes, it was shown that not all intracellular Na + ions are in the extreme narrowing limit. The triple quantum coherence filtered experiments resulted in an observed R 2f = 2022 ± 302 s −1 and R 2s = 200 ± 28 s −1. From spin-echo experiments we obtained R 2f = 2200 ± 355 s −1 and a R 2s = 145 ± 15 s −1. These values are similar to those found in other cell systems and indicate water-Na +-protein interactions. Using single quantum NMR, the Na + permeability of the endothelial membrane was determined. To obtain the Na + transcellular permeability coefficient the cells were treated with 50 μM ouabain in the perfusion medium. Ouabain inhibits the Na-K pump and caused the intracellular Na + concentration to increase in time. The permeability coefficient was obtained from the time dependence of the intracellular Na + concentration. Assuming a monolayer of rectangularly shaped cells, we obtained a value of P = 0.02 · 10 −5 cm s −1.