Upregulation of γ-aminobutyric acid transporter expression: role of alkylated γ-aminobutyric acid derivatives

Pregabalin [(S)-(+)-3-isobutylgaba] and gabapentin [1-(aminomethyl)cyclohexane acetic acid] are γ-aminobutyric acid (GABA) derivatives that are effective in the treatment of behavioural disorders, convulsions, epilepsy and hyperalgesia. The mechanisms underlying the diverse actions of these compounds in the brain have not been well elucidated. To test the hypothesis that these compounds exert some of their effects on GABA-ergic systems in the brain, we examined their role in regulating the rat brain GABA transporter GAT1, a plasma membrane protein involved in regulating synaptic transmitter levels. Prolonged incubation of hippocampal cultures, which endogenously express GAT1, with gabapentin and pregabalin caused a 2-fold increase in subsequent GABA uptake, which was concentration- and time-dependent. This increase in uptake was correlated with a redistribution of GAT1 protein from intracellular locations to the plasma membrane. Further experiments also suggested that the signal transduction cascade that modulates pregabalin-mediated GAT1 redistribution may involve pathways activated by specific GAT1 substrates and antagonists but does not involve protein kinase C and tyrosine kinases, two other pathways known to regulate GAT1 redistribution. These data suggest that pregabalin and gabapentin may exert some of their actions in the brain by altering GABAergic signalling.