High affinity uptake systems for glycine, glutamic and aspartic acids in synaptosomes of rat central nervous tissues

We have studied the kinetics of uptake of several l-amino acids into homogenates of rat cerebral cortex and spinal cord. These accumulated amino acids are localized to synaptosomal fractions obtained by sucrose density gradient centrifugation. The accumulations of glutamic and aspartic acids in the cerebral cortex and spinal cord and glycine in the spinal cord are best described by two kinetic systems with low and high affinities respectively. By contrast, for glycine in the cerebral cortex and for several other amino acids in both areas, only single low affinity transport systems are detected. The uptakes of glutamic and aspartic acids were mutually competitive in both cerebral cortical and spinal cord preparations, suggesting that they utilize the same uptake mechanism.