NA+-DEPENDENT HIGH-AFFINITY UPTAKE OF L-GLUTAMATE IN CULTURED FIBROBLASTS

Uptake of 1-mu-M [H-3]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 Ca2+ (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-mu-M. 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.