LI-7 AND NA-23 NUCLEAR-MAGNETIC-RESONANCE STUDIES OF TRANSPORT AND DIFFUSION IN LIPOSOMES - COMPARISON OF TRANSPORT RATE CONSTANTS ESTIMATED USING PULSED-FIELD GRADIENT AND MAGNETIZATION-TRANSFER PROCEDURES

The 'two-region approximation' to pulsed field gradient (PFG) NMR studies of heterogeneous systems has been applied to the estimation of the rates of ionophore-mediated transmembrane exchange of Li+ in liposomes. Transport modulation of restricted diffusion, originally observed for hypophosphite in human erythrocytes, was also seen in the suspensions of liposomes with Na+ and Li+ transport. There was good agreement between the transmembrane exchange rate constants estimated from PFG and magnetization-transfer Li-7 NMR experiments. Thus PFG experiments are likely to be a viable alternative to 'dynamic' NMR methods for measuring rapid transport rates in those biological systems which do not display a significant difference in chemical shift, or relaxation rate, of the transmembrane-distributed species.