Diaminobutyric acid: A tool for discriminating between carrier-mediated and non-carrier-mediated release of GABA from synaptosomes?

The carrier-mediated transport of GABA in rat brain synaptosomes was strongly and permanently inhibited byL-2,4-diaminobutyric acid (DAB). In order to discriminate between carrier-mediated and non-carrier-mediated release of [(3)H]GABA, synaptosomes prelabeled with 0.5 μM [(3)H]GABA in the presence of 100 μM DAB, or with 0.2 μM [(3)H]GABA without DAB, were superfused in conditions stimulating the release of [(3)H]GABA. Only the release elicited by unlabeled GABA or DAB (by homo- and heteroexchange, respectively) was strongly inhibited in DAB-pretreated synaptosomes. The spontaneous release and the release induced by 56 mM KCl in the presence of CaCl2, by the ionophore A23187, by ouabain, by lack of K(+), or by purified black widow spider toxin were unaffected or only barely decreased in DAB-treated synaptosomes, and therefore do not seem to be mediated by the DAB-blocked GABA carrier.