Potassium-induced release of amino acids from cerebral cortex and spinal cord slices of the rat

We have examined the release of exogenous amino acids from central nervous system slices following potassium depolarization. Pronounced glycine release was observed from spinal cord but not cerebral cortex, while glutamic and aspartic acids were released similarly from both regions. γ-aminobutyric acid and proline were released more from cerebral cortex than spinal cord. Much less release from either area was detected with α-aminoisobutyric acid, arginine, histidine, lysine, alanine, serine, phenylalanine or tyrosine. Potassium-induced release of γ-aminobutyric acid, glutamic and aspartic acids and proline was greatly diminished in calcium-free medium. Depletion of sodium during labeling of slices with radioactive amino acids markedly reduced subsequent amino acid release. High affinity uptake of amino acids into apparent neurotransmitter pools is much more sodium-dependent than low affinity uptake of the same amino acids. Accordingly, potassium-induced 'transmitter' amino acid release appears to involve pools labeled by the high affinity, sodium requiring uptake systems.