Transport of tryptophan and tyrosine in rat brain slices in the presence of lithium.

Slices from rat cerebral cortex, brain stem, and cerebellum were incubated in media in which 1, 10, or 100 mmol/liter NaC1 had been replaced by equimolar amounts of LiC1. The initial influx of tryptophan and tyrosine into the slices diminished in the lithium-containing media. The lithium-induced inhibition was not competitive. The equilibrium accumulation of the amino acids was also less in the presence of LiC1. The incorporation of tryptophan and tyrosine into the proteins of the slices was inhibited by lithium. These were no clear differences between the brain areas studied. It has been suggested earlier that a lithium treatment enhances the in vivo cerebral uptake of these aromatic amino acids. The present results show that such a possible increase in uptake is not a direct effect of lithium ions on cell membranes.