Application de la RMN du Na 23 à l'étude des échanges ioniques

One single line is usually observed in the Na NMR spectra of biological systems. Some anionic paramagnetic species interacting with the sodium shift the sodium signal. So long as it does not enter the cell, a shift reagent splits the resonance line into two components: the intra (unshifted) and the extracellular Na (shifted). The method is applied to intestinal epithelium and to erythrocytes. Extracellular medium is enriched with dysprosium tripolyphosphate 2,5 mM. Na-K pump activity is studied in human erythrocytes. Ouabain (10 M) inhibition can be followed by the increase of the internal Na peak on the successive spectra whereas it does not change in the control. Na efflux out of the Na loaded erythrocytes can be measured as well. After incubation in a recovering medium, intracellular Na, as calculated from the successive spectra, returns progressively to normal. Simultaneously, the external peak shift reduces. This method can successfully demonstrate attenuations of the Na-K pump in pathological circumstances, such as chronic renal failure . The effects of polyether antibiotics on the sodium transport are also studied by this way. For instance, monensin causes a swift Na efflux that transiently broadens the external signal. Using shift reagent, Na NMR is an efficient tool for ionic membrane exchange studies.