Transport of monoamine and amino acid neurotransmitters by primary astroglial cultures

The transport of ³H]l-glutamate, ³H]l-aspartate, ³H]-aminobutyric acid (³H]GABA), ³H]dopamine, ³H]norepinephrine and ³H]5-hydroxytryptamine (³H-5-HT) was measured in primary astroglial cultures from newborn rat cerebral hemispheres. There was a high-affinity uptake with aK _m of 69.0 M for L-glutamate, 12.3 M forl-aspartate and 3.1 M for GABA. The uptake showed properties of high capacity with aV _max of 17.0 nmol·mg prot^–1·min^–1 forl-glutamate, 1.1 nmol·mg prot^–1·min^–1 forl-aspartate and 0.04 nmol·mg prot^–1·min^–1 for GABA. No high-affinity high capacity transport system was found for the monoamines studies. Autoradiographic examination demonstrated a heavy deposit of grains suggesting a prominent accumulation of ³H]l-glutamate and ³H]l-aspartate in the astroglial-like cells of the cultures, while the ³H]GABA accumulation was less intense. On the other hand, there was only a weak accumulation of grains after incubating the cultures with ³H]dopamine, ³H]norepinephrine or ³H]5-HT. Thus, astroglial cells in culture accumulate amino acid neurotransmitters and monoamines in different ways with a high-affinity high-capacity uptake of glutamate, aspartate and GABA and a diffusion-uptake of dopamine, norepinephrine and 5-HT.