Direct high-resolution nuclear magnetic resonance studies of cation transport in vivo, Na+ transport in yeast cells.

A new nuclear magnetic resonance (NMR) method for monitoring transmembrane metal cation transport is reported. It is illustrated with a study of Na(+) efflux from Na(+)-rich yeast cells. The technique involves the use of an anionic paramagnetic shift reagent, present only outside the cells, to induce a splitting of the sodium-23 NMR peak, in this case, into components representing intra- and extracellular Na(+). The time course of the efflux is in good agreement with the literature and can be well fitted with a double exponential decay expression. Splitting of the lithium-7 NMR signal from a suspension of Li(+)-rich respiratory-deficient, petite yeasts is also reported.