Transport of monoamine and amino acid neurotransmitters by primary astroglial cultures.

The transport of [3H]L-glutamate, [3H]L-aspartate, [3H] gamma-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 a Km of 69.0 microM for L-glutamate, 12.3 microM for L-aspartate and 3.1 microM for GABA. The uptake showed properties of high capacity with a Vmax of 17.0 nmol X mg prot-1 X min-1 for L-glutamate, 1.1 nmol X mg prot-1 X min-1 for L-aspartate and 0.04 nmol X mg prot-1 X min-1 for GABA. No high-affinity high capacity transport system was found for the monoamines studied. 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.