Na+‐dependent high‐affinity uptake of l‐glutamate in cultured fibroblasts

Abstract

Uptake of 1 μM[ 3 H] l -glutamate by cultured 3T3 fibroblasts was strongly dependent on extracellular Na + ; it was reduced by elevated concentrations of K + (60 mM) but it was not influenced by variations in the concentration of Ca 2+ (0–9.6 mM). d - and l -Asparate, d - and l - threo -3-hydroxyaspartate dl - threo -3-methylaspartate and a few other glutamate derivatives and analogues inhibited the uptake but several close analogues of l -glutamate (including d -glutamate) had no effect, implying that the uptake system is highly structurally selective. The recently identified inhibitor of glutamate uptake in synaptosomal preparations, l - trans -pyrrolidine-2,4-dicarboxylate, was also among the inhibitors. Apparent K m of the uptake was found to be < 10 μM. The present observations indicate that Na + -dependent ‘high-affinity’ uptake of l -glutamate may appear in structures which are apparently unrelated to glutamatergic synaptic transmission in the CNS.