A Comparative Study and Partial Characterization of Multi-Uptake Systems for γ-Aminobutyric Acid

Previous work by the authors had indicated that synaptosome-enriched preparations from the cerebral cortex of the rat contained a high-, a medium-, and a low-affinity uptake system for gamma-aminobutyric acid (GABA). The present study demonstrated that this phenomenon also prevailed in synaptosomes from rat diencephalon, mesencephalon, and cerebellum, although the Vmax values for the high- and medium-affinity systems in the cerebellum were very low relative to those of the other regions. When a different type of preparation containing nerve endings (glomeruli) was obtained from the cerebellum, it possessed a Vmax value for the high-affinity system that was more similar to that for the corresponding system in synaptosomes from the other brain regions. In contrast to the above situation, synaptosomes from rat olfactory bulb lacked the low-affinity uptake system, as did synaptosomes from dog olfactory bulb. The aspartate/glutamate uptake systems, as measured with D-aspartate, provided a regional pattern quite different from those of GABA uptake. Only two uptake systems, a high- and low-affinity system, were observed in all regions tested. All three GABA uptake systems were present in cortical synaptosomes from the mouse, hamster, and guinea pig, and all three systems were sodium dependent, energy dependent, temperature sensitive, and totally inhibited by nipecotic acid.