23 Na NMR measurement of the maximal rate of active sodium efflux from human red blood cells

The method for 23 Na NMR measurement of the maximal rate of active Na + efflux from human red blood cells (RBC) is proposed. The nonpenetrating paramagnetic shift reagent (SR) bis(tripolyphosphate)dysprosium(III) complex is used to distinguish extracellular Na + ions from intracellular. RBC are proved to retain their physiological activity in the presence of SR. Intracellular Na + is shown to be 100% NMR visible. The levels of intracellular and extracellular Na + and K + ions are changed to decrease their concentration gradients across the erythrocyte membrane to make active Na + efflux the only 23 Na NMR measurable process; so the integrated areas of intra‐and extracellular Na + peaks remain invariant throughout the incubation period in the presence of 0.25 m M ouabain, a specific inhibitor of Na + , K + ‐ATPase. The accuracy of the proposed technique is evaluated to be 10%. The maximal Na + efflux is determined to be 10.1 ± 1.0 m M /h/liter of Cells. © 1989 Academic Press, Inc.