23Na-NMR study of cation cotransport in human red blood cells

Na(+)-K+ cotransport in human erythrocytes from healthy subjects has been studied by means of 23Na-nuclear magnetic resonance (NMR) in the presence of the anionic paramagnetic shift reagent dysprosium (III) tripolyphosphate [Dy(PPP)2(7-)]. The intra- and extracellular 23Na-NMR signals were well separated, giving values of 6 +/- 1 mM for internal sodium concentration. Determination of the furosemide-sensitive Na+ efflux, in the presence of ouabain, was obtained by correlating the chemical shift variation of the external signal with changes in external Na+ concentration. For this purpose, calibration curves were generated. The values of the maximum efflux velocity (Vmax; 0.29-1 mmol.h-1.l cells-1) measured in 10 healthy adult male subjects were found to be within the range of values obtained by other authors. The NMR method proposed for the study of Na(+)-K+ cotransport is relatively simple and allows quick evaluation of cotransport Vmax values for a number of samples, being a good candidate for the study of this transport mechanism in the presence of different pathologies.