Specific glycine--accumulating synaptosomes in the spinal cord of rats

Subcellular fractionation of rat spinal cord on continuous sucrose density gradients provides evidence for the existence of a specific synaptosomal fraction (enriched in pinched-off nerve endings) that accumulates glycine selectively by way of a high-affinity transport system. The particles in this fraction sediment to a less-dense portion of sucrose gradients than do particles that accumulate neutral, basic, aromatic, and acidic amino acids. Particles accumulating gamma-aminobutyric acid are even less-dense than those storing exogenous glycine. The glycine-specific synaptosomal fraction also exists in the brain stem but not in the cerebral cortex. These findings provide neurochemical support for the suggestion that glycine has a specialized synaptic function, perhaps as neurotransmitter, in mammalian spinal cord.