Lamotrigine inhibits Ca2+ currents in cortical neurons: functional implications.

In pyramidal cortical cells, high-voltage-activated Ca2+ currents affect seizure propagation and the release of excitatory amino acids at the corticostriatal axon terminals. The new antiepileptic drug lamotrigine (Lamictal) produced a large and dose-dependent inhibition of high-voltage-activated Ca2+ currents (IC50 = 12.3 microM) in rat cortical neurons. This action was not blocked by the dihydropyridine receptor antagonist nifedipine; instead, the response was blocked by the concomitant application of the N-type Ca2+ channel blocker, omega-conotoxin GVIA (1-3 microM) and the P-type Ca2+ channel blocker, omega-agatoxin-IVA (20-100 nM). These findings demonstrate that lamotrigine, at therapeutic doses, is capable of modulating the Ca2+ conductances involved in excitatory amino acid release in the corticostriatal pathway, partially explaining lamotrigine usefulness in the therapy of epilepsy as well as in the treatment of excitatory amino acid-induced neurotoxicity.