Amino acid neurotransmitter candidates: sodium-dependent high-affinity uptake by unique synaptosomal fractions

Glutamic and aspartic acids and glycine are accumulated by high-affinity uptake systems into synaptosomal preparations in central nervous tissue. Sodium is required by these high-affinity transports, but not by the low-affinity transports for these and other amino acids. The sodium-requiring amino acid uptake systems label unique synaptosomal fractions. Observations suggest that these amino acids serve specific synaptic functions, presumably as neurotransmitters.