Long-lasting decrease in neuronal Ca2+/calmodulin-dependent protein kinaseII activity in a hippocampal neuronal culture model of spontaneous recurrent seizures

Ca2+/calmodulin-dependent protein kinase II (CaM Kinase II) activity was ev aluated in a well-characterized in vitro model of epileptiform activity. Lo ng-lasting spontaneous recurrent seizure (SRS) activity was induced in hipp ocampal neuronal cultures by exposure to low Mg2+ media for 3 h. Analysis o f endogenous Ca2+/calmodulin-dependent phosphorylation revealed a significa nt long-lasting decrease in P-32 incorporation into the or (50 kDa) and bet a (60 kDa) subunits of CaM kinase II in association with the induction of S RS activity in this preparation. Ca2+/calmodulin-dependent substrate phosph orylation of the synthetic peptides, Autocamtide-2 and Syntide II, was also significantly reduced following the induction of SRSs and persisted for th e life of the neurons in culture. The decrement in CaM kinase Il activity a ssociated with low Mg2+ treatment remained significantly decreased when val ues were corrected for changes in levels of a subunit immunoreactivity and neuronal cell loss. Addition of the protein phosphatase inhibitors, okadaic acid and cyclosporin A, to the phosphorylation reaction did not block the SRS-associated decrease in substrate phosphorylation, indicating that enhan ced phosphatase activity was not a contributing factor to the observed decr ease in phosphate incorporation. The findings of this study demonstrate tha t CaM kinase Il activity is decreased in association with epileptogenesis o bserved in these hippocampal cultures and may contribute to the production and maintenance of SRSs in this model. (C) 1999 Published by Elsevier Scien ce B.V. All rights reserved.