Epileptogenesis causes an N-methyl- d-aspartate receptor/Ca 2+-dependent decrease in Ca 2+/calmodulin-dependent protein kinase II activity in a hippocampal neuronal culture model of spontaneous recurrent epileptiform discharges

Abstract

Alterations in the function of Ca 2+/calmodulin-dependent protein kinase II (CaM kinase II) have been observed in both in vivo and in vitro models of epileptogenesis; however the molecular mechanism mediating the effects of epileptogenesis on CaM kinase II has not been elucidated. This study was initiated to evaluate the molecular pathways involved in causing the long-lasting decrease in CaM kinase II activity in the hippocampal neuronal culture model of low Mg 2+-induced spontaneous recurrent epileptiform discharges (SREDs). We show here that the decrease in CaM kinase II activity associated with SREDs in hippocampal cultures involves a Ca 2+/ N-methyl- d-aspartate (NMDA) receptor-dependent mechanism. Low Mg 2+-induced SREDs result in a significant decrease in Ca 2+/calmodulin-dependent substrate phosphorylation of the synthetic peptide autocamtide-2. Reduction of extracellular Ca 2+ levels (0.2 mM in treatment solution) or the addition of dl-2-amino-5-phosphonovaleric acid (APV) 25 µM blocked the low Mg 2+-induced decrease in CaM kinase II-dependent substrate phosphorylation. Antagonists of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainic acid receptor or L-type voltage sensitive Ca 2+ channel had no effect on the low Mg 2+-induced decrease in CaM kinase II-dependent substrate phosphorylation. The results of this study demonstrate that the decrease in CaM kinase II activity associated with this model of epileptogenesis involves a selective Ca 2+/NMDA receptor-dependent mechanism and may contribute to the production and maintenance of SREDs in this model.