Dynamic NMR measurement of volume regulatory changes in Amphiuma RBC Na+ content

23Na nuclear magnetic resonance (NMR) and conventional chemical methods were employed to measure Na+ fluxes in Amphiuma red blood cells (RBC) during volume regulation. Paramagnetic shift reagent [dysprosium triethylenetetraminehexaacetic acid (DyTTHA) and dysprosium tripolyphosphate (Dy(TPP)2)] were used to alter extracellular Na+ magnetic resonance. Data are presented describing 23Na resonance dependence on shift reagent, sodium and calcium concentration. The authors confirmed that the shift reagents neither enter the cells nor alter intracellular Na+, K+, and Cl- concentrations under control conditions when extracellular calcium was maintained >0.5 mM. They also confirmed that the shift reagent complexes chelate calcium [Dy(TPP)2 much more so than DyTTHA] and that their toxic effects could be alleviated by adjusting calcium in the cell's suspension medium to control levels. In parallel experiments, where volume-activated Na+ fluxes range from 0.3 to 3 mmol Na+/kg dry cell solid (DCS) x minute in cells containing from 30 to 150 mmol Na+/kg DCS, changes in intracellular sodium measured by 32Na NMR were within 4% of those measured by conventional destructive methods. Finally, they present data that are consistent with the interpretation that 6 mmol Na+/kg DCS plus 16% of intracellular Na+ is NMR invisible