Effects of carbamazepine, phenytoin, valproic acid, oxcarbazepine, lamotrigine, topiramate and vinpocetine on the presynaptic Ca2+ channel-mediated release of [3H]glutamate: comparison with the Na+ channel-mediated release.
The effect of carbamazepine, phenytoin, valproate, oxcarbazepine, lamotrigine and topiramate, that are among the most widely used antiepileptic drugs (AEDs), and of the new putative AED vinpocetine on the Ca(2+) channel-mediated release of [(3)H]Glu evoked by high K(+) in hippocampal isolated nerve endings was investigated. Results show that carbamazepine, oxcarbazepine and phenytoin reduced [(3)H]Glu release to high K(+) to about 30% and 55% at concentrations of 500 microM and 1500 microM, respectively; lamotrigine and topiramate to about 27% at 1500 microM; while valproate failed to modify it. Vinpocetine was the most potent and effective; 50 microM vinpocetine practically abolished the high K(+) evoked release of [(3)H]Glu. Comparison of the inhibition exerted by the AEDs on [(3)H]Glu release evoked by high K(+) with the inhibition exerted by the AEDs on [(3)H]Glu release evoked by the Na(+) channel opener, veratridine, shows that all the AEDs are in general more effective blockers of the presynaptic Na(+) than of the presynaptic Ca(2+) channel-mediated response. The high doses of AEDs required to control seizures are frequently accompanied by adverse secondary effects. Therefore, the higher potency and efficacy of vinpocetine to reduce the permeability of presynaptic ionic channels controlling the release of the most important excitatory neurotransmitter in the brain must be advantageous in the treatment of epilepsy.
Sitges
María
M
Departamento de Biología Celular y Fisiología, Instituto de Investigaciones Biomédicas, UNAM, Apartado Postal 70228, Ciudad Universitaria 04510, México D.F., Mexico. sitges@biomedicas.unam.mx
Guarneros
Araceli
A
Nekrassov
Vladimir
V
D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000648:ultrastructure; D008297:Male; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D026941:Sodium Channel Blockers / Q000494:pharmacology; D015222:Sodium Channels / Q000502:physiology*; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D014316:Tritium / Q000378:metabolism; D020867:omega-Agatoxin IVA / Q000494:pharmacology
D000927:Anticonvulsants; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D020867:omega-Agatoxin IVA; D014316:Tritium; D018698:Glutamic Acid; D013779:Tetrodotoxin; D011188:Potassium