Characteristics of synaptosomal tyrosine uptake in various brain regions: Effect of other amino acids

Tyrosine uptake by rat synaptosomes was maximal after 5–10 min of incubation and at 30°C; uptake was inhibited by dinitrophenol (10^?4 M) or ATP (10^?3 M) and increased by reducing sodium concentrations or increasing calcium or potassium. The best model for uptake is a two-carrier system, in which one carrier shows high-affinity uptake and the other may be diffusional. Both uptake mechanisms are more concentrated in catecholamine-rich brain areas, and are inhibited $\text{in vitro}$ by other large, neutral amino acids. At physiologic amino acid brain concentrations, each system probably carries about half of the tyrosine into the nerve terminal.