AMINO-ACID NEUROTRANSMISSION - DYNAMICS OF VESICULAR UPTAKE

Glutamate, GABA and glycine, the major neurotransmitters in CNS, are t aken up and stored in synaptic vesicles by a Mg2+-ATP dependent proces s. The main driving force for vesicular glutamate uptake is the membra ne potential, whereas both the membrane potential and the proton gradi ent contribute to the uptake of GABA and glycine. Glutamate is taken u p by a specific transporter with no affinity for aspartate. Evans blue and related dyes are competitive inhibitors of the uptake of glutamat e. GABA, beta-alanine, and glycine an taken up by the same family of t ransporter molecules. Aspartate, taurine, and proline are not taken up by any synaptic vesicle preparations. It is suggested that vesicular uptake and release are characteristics that identify these amino acids as neurotransmitters. We also discuss that ''quanta'' in the brain ar e not necessarily related the content of neurotransmitter in the synap tic vesicles, but rather to postsynaptic events.