NA-23 NUCLEAR-MAGNETIC-RESONANCE STUDY OF INTRACELLULAR SODIUM IN VASCULAR ENDOTHELIAL-CELLS

Na-23(+)-NMR was used to determine the intracellular mobility and cell membrane permeability of Na+ in porcine vascular endothelial cells. T he cells were grown as monolayers onto microcarrier beads and perfused with a medium containing Dy(P3O10)(2)(7-) to shift the extracellular from the intracellular Na+ resonance. Using triple quantum coherence f iltered NMR experiments and spin echoes, it was shown that not all int racellular Na+ ions are in the extreme narrowing limit. The triple qua ntum coherence filtered experiments resulted in an observed R(2f) = 20 22 +/- 302 s(-1) and R(2s) = 200 +/- 28 s(-1). From spin-echo experime nts 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, th e Na+ permeability of the endothelial membrane was determined. To obta in the Na+ transcellular permeability coefficient the cells were treat ed with 50 mu M ouabain in the perfusion medium. Ouabain inhibits the Na-K pump and caused the intracellular Na+ concentration to increase i n time. The permeability coefficient was obtained from the time depend ence of the intracellular Na+ concentration. Assuming a monolayer of r ectangularly shaped cells, we obtained a value of P = 0.02.10(-5) cm s (-1).