Fluoride transmembrane exchange in human erythrocytes measured with 19F NMR magnetization transfer.

19F NMR spectra of sodium fluoride in suspensions of human erythrocytes were seen to yield separate resonances for the F- populations inside and outside the cells. Selective saturation of the magnetization of the intracellular population gave rise to transfer of that saturation to the extracellular population. The extent of magnetization transfer was high and it was blocked by the capnophorin (band 3) anion exchange inhibitor 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS). A series of magnetization-inversion transfer experiments was carried out for the range of intracellular fluoride concentrations of 11 mM to 136 mM and analysed using one-dimensional 'overdetermined' exchange analysis. This yielded an estimate of the equilibrium exchange Michaelis constant and maximal velocity of 27 +/- 3 mM and 180 +/- 5 x 10(-16) mol cell-1 s-1, respectively. There was no alteration of exchange flux of fluoride at an intracellular concentration of 49 mM in the presence of 50 mM glucose; thus suggesting no interaction between glucose and anions in capnophorin-mediated exchange of solutes.