Transport kinetics for the uptake of (3H)glycine and (3H)L-glutamate into dorsal and ventral slices of rat spinal cord

Na+-dependent high-affinity uptake ofl-glutamate in cultured fibroblasts

Uptake of 1 microM [3H]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 Km of the uptake was found to be less than 10 microM. 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.

Na(+)-dependent high affinity uptake of L-glutamate in primary cultures of human fibroblasts isolated from three different types of tissue

Cultured human fibroblasts isolated from embryonic muscle, skin and peripheral nerve tissues were found to accumulate [3H]L-glutamate by a Na(+)-dependent uptake process strongly inhibited by several glutamate/aspartate analogues including D- and L-aspartate, D- and L-threo-3-hydroxyaspartate and L-trans-pyrrolidine-2,4-dicarboxylate but not D-glutamate. It was also reduced by elevated concentrations of K+, Rb+ and Cs+. The values of Km's were 5-20 microM, well within the 'high affinity' region. Variations in the capacity (Vmax) of [3H]L-glutamate uptake did not correlate with the origin (muscle, skin or nerve tissue) of the fibroblasts. The uptake characteristics suggest that it is mediated by a transport system similar to that commonly observed only in brain tissue.