[³H] γ-aminobutyric acid transport in rat substantia nigra pars reticulata synaptosomes: Pharmacological characterization and phorbol ester-induced inhibition

In synaptosomes from rat substantia nigra pars reticulata, [³H] γ-aminobutyric acid (GABA) uptake was inhibited by GABA, (±)-nipecotic acid, β-alanine and SKF 89976-A. Inhibition was concentration-dependent and monophasic, with IC₅₀ values that agree with those reported for the cloned rat GABA transporter GAT-1. [³H]GABA uptake was modestly, but significantly, reduced (21±3% inhibition) by 100 nM phorbol 12-tetradecanoyl-13-acetate (TPA), an activator of protein kinase C (PKC). The inhibitory action of TPA was reversed by the PKC inhibitor staurosporine (100 nM). Saturation analysis revealed that TPA reduced the maximum capacity of transport with no change in the affinity for GABA. [³H]GABA uptake was unaffected by either forskolin (10 μM) or 8-bromo-cAMP (500 μM). These results indicate that SNr GABAergic afferents express the GAT-1 transporter whose activity can be regulated by a PKC-mediated mechanism. Copyright (C) 1999 Elsevier Science Ireland Ltd.