On the inhibition of GABA release from a preparation of rat brain nerve-endings by SKF 89976-A, a GABA uptake inhibitor

Fractions enriched in nerve-terminals were made in order to investigate the release of γ-aminobutyric acid (GABA). A P₂-preparation made from whole rat brain was pre-labeled with [³H]GABA and thereafter incubated in high concentrations (1 mM) of the GABA uptake inhibitor SKF 89976-A. The nerve-terminals were thereafter incubated in depolarizing concentrations of KCl and finally the medium and nerve-terminals separated by a filtration procedure. The amount of [³H]GABA present on the filter and in the supernatant was measured by liquid scintillation counting and used to assess the release rate. SKF 89976-A reduced the KCl-induced efflux of [³H]GABA from the nerve-terminals. The inhibition was as effective against KCl-induced [³H]GABA efflux in the presence as well as in the absence of Ca²⁺. Our finding may demonstrate an inhibition of the inside-out activity of the GABA transporter.