On the existence of two GABA pools associated with newly synthesized GABA and with newly taken up GABA in nerve terminals

¹⁴C]Glutamic acid and ³H]GABA were injected into the lateral ventricle of mouse and then ¹⁴C]GABA and ³H]GABA in synaptosomes isolated from the animals were analysed. The ¹⁴C]GABA was interpreted to be newly synthesized GABA from ¹⁴C]glutamic acid while the ³H]GABA to be newly taken up GABA. We have obtained the following results: (1) when the animals were pretreated with aminooxyacetic acid and thus the GABA content in synaptosomes increased to about 2 times of the control level, only the ³H]GABA was enhanced to 3 times of the control level without any change of ¹⁴C]GABA, (2) the release of ¹⁴C]GABA from synaptosomes by high K⁺ depolarization was 1.5 times greater than that of ³H]GABA, (3) the releases of both ¹⁴C]GABA and ³H]GABA were increased in the presence of cold GABA,l-2,4-diaminobutyric acid or γ-amino-β-hydroxybutyric acid, but only slightly increased in the presence of β-alanine. These results would suggest that newly synthesized GABA and newly taken up GABA localized individually in different pools, which might localize either in different nerve terminals or separately in the same nerve terminal.