High-resolution NMR studies of transmembrane cation transport: use of an aqueous shift reagent for 23Na.

Abstract

23Na NMR studies of large unilamellar vesicles of egg lecithin in salt solutions are reported. A shift reagent, the dysprosium nitrilotriacetate ion Dy[N(CH2CO2)3]3-2 was used to distinguish between 23Na+ inside and outside the vesicles. When both are present and the shift reagent is present on only one side, 2 clearly distinct resonances are observed. Creation of a Na+ concentration gradient and subsequent catalysis of passive transport induced by the introduction of gramicidin can be monitored easily by using the relative intensities of the 2 resonances. Transport both out of and into vesicles was observed.