Differential involvement of L-type calcium channels in epileptogenesis of rat hippocampal slices during ontogenesis

Organic calcium channel antagonists block epileptiform activity in adult ti ssue, suggesting an essential role of L-type channels in epileptogenesis in the mature CNS. By contrast, this remains doubtful for neonatal tissue, as the density of calcium channels changes markedly with ontogenesis. The pap er addresses this question by exploring the antiepileptic efficacy of the L -type calcium channel blockers verapamil and nifedipine in low-Mg2+-epileps y in rat hippocampal slices of different postnatal (PN) ages. Field (CA3, C A1) and membrane potentials (CA3) were recorded. Washout of Mg2+ induced ep ileptiform potentials, which were blocked age-dependently: Verapamil suppre ssed activity in all preparations of PN1-5 and PN13-30+, but only in 70% of PN6-12. Nifedipine depressed activity in >75% of slices of PN13-30+, but o nly in 33% of PN1-12. The findings indicate a role of L-type calcium channe ls in epileptogenesis from PN13 onwards, with phenylalkylamine-sensitive ca lcium channels also being involved during PN1-5. (C) 2000 Academic Press.