Characteristics of excitatory amino acid uptake in cultures from neurons and glia from the retina

Abstract

3H-D-Aspartate uptake was biochemically characterized in cultures from chick retina enriched in glial (Müller) cells or neurons during progressive days in vitro (DIV). In the neuronal cultures a high-affinity, Na(+)-dependent system was found with Km = 8-13 microM and pharmacological characteristics in agreement with those of reuptake systems in other regions of the CNS. The uptake system in glial cells showed a lower affinity, with Km = 100-135 microM. In both cases, uptake was temperature and energy dependent. A sharp increase in the Vmax of uptake was observed in both neuronal and glial cultures at 5 DIV, at which time morphologically mature synapses have been shown to be present in retinal cultures. A parallel increase in the pharmacological specificity of the uptake system in neuronal cultures was observed, with a rise in the efficiency of D-Asp, L-Asp, L-Glu, and DL-asp- beta-hydroxamate for inhibiting 3H-D-Aspartate uptake. Results suggest the possibility of reuptake participating in the regulation of extracellular glutamate concentration during development.