Substrate specificity of uptake of diamines in mouse brain slices

Brain slices upon incubation accumulate diamines (cadaverine and putrescine) from the medium against a concentration gradient up to an intracellular-to-medium ratio of 8. The transport system is different from the various systems for amino acids, among which is the transport system for basic amino acids. Diamine uptake, in contrast to amino acid uptake, is independent of Na⁺ and is increased at higher pH. There is some overlap among these transport classes—basic amino acids have a low affinity to the diamine system and some heteroexchange (stimulation of uptake) can be observed at very high concentrations between diamines and some amino acids (glycine, β alanine, γ-aminobutyrate, possibly also with proline and taurine). The diamine system seems also to be separate from the monoamine uptake systems. The results indicate the presence of numerous systems for metabolite transport in the brain with some overlap between systems.