Gabapentin inhibits the activity of the rat excitatory glutamate transporter 3 expressed in Xenopus oocytes

Gabapentin, a derivative of gamma-aminobutyric acid (GABA), is used to treat epilepsy and neuropathic pain. The pharmacological mechanisms for gabapentin effects are not completely elucidated. We investigated the effect of gabapentin on the activity of excitatory amino acid transporter 3 (EAAT3) that can regulate extracellular glutamate concentrations. EAAT3 was expressed in Xenopus oocytes. Membrane currents were recorded after application of L-glutamate in the presence or absence of different concentrations of gabapentin (1-300 mu M) by using a two-electrode voltage clamp. To determine the effect of gabapentin on V-max and K-m of EAAT3 for L-glutamate, L-glutamate at 3-300 mu M was used. To study the effects of protein kinase C (PKC) and phosphatidylinositol 3-kinase (PI3K) on gabapentin-induced changes in EAAT3 activity, oocytes were incubated with the PKC activator (Phorbol 12-myristate 13-acetate, PMA), the PKC inhibitors (chelerythrine or staurosporine), and the PI3K inhibitor wortmannin. Gabapentin decreased EAAT3 activity in a concentration-dependent manner and EAAT3 activity was significantly inhibited by 10-300 mu M gabapentin. Gabapentin significantly decreased V-max without affecting K-m. PMA increased EAAT3 activity; however, gabapentin attenuated the PMA-induced increase in EAAT3 activity. Pre-incubation of oocytes with chelerythrine, staurosporine, or wortmannin decreased basal EAAT3 activity, which was further reduced by gabapentin. We conclude that gabapentin decreases EAAT3 activity at clinically relevant and higher concentrations, in which PKC and PI3K may not be involved. The results suggest that EAAT3 might not be a target for the anticonvulsant action of gabapentin. (C) 2015 Elsevier B.V. All rights reserved.