Effects of gabapentin and pregabalin on K+-evoked 3H-GABA and 3H-glutamate release from human neocortical synaptosomes

One site of action of the anticonvulsant, analgesic, and anxiolytic drugs gabapentin and pregabalin is the alpha(2)delta-subunit of voltage-sensitive Ca2+ channels (VSCC). We therefore analyzed the effects of gabapentin and pregabalin on K+-evoked release of H-3-gamma- aminobutyric acid (GABA) and H-3-glutamate from superfused human neocortical synaptosomes. These neurotransmitters are released by Ca2+-dependent exocytosis and by Ca2+-independent uptake reversal. When a GABA transport inhibitor was present throughout superfusion to isolate exocytotic conditions, gabapentin and pregabalin (100 mu M each) reduced K+-evoked H-3-GABA release by 39% and 47%, respectively. These effects were antagonized by the alpha(2)delta-ligand L-isoleucine (1 mu M) suggesting the alpha(2)delta-subunit of terminal VSCC to mediate the reduction of exocytosis. Both drugs had no effect on exocytotic H-3-glutamate release and also failed to modulate the release of H-3-GABA and H-3-glutamate caused by reversed uptake in the absence of external Ca2+. Thus, an inhibition of glutamate release by gabapentin and pregabalin as main anticonvulsant principle is not supported by our experiments. An anticonvulsant mode of action of both drugs may be the reduction of a proconvulsant exocytotic GABA release.