Altered calcium/calmodulin kinase II activity changes calcium homeostasis that underlies epileptiform activity in hippocampal neurons in culture

Epilepsy is characterized by the occurrence of spontaneous recurrent epileptiform discharges (SREDs) in neurons. A decrease in calcium/calmodulin-dependent protein kinase II (CaMK-II) activity has been shown to occur with the development of SREDs in a hippocampal neuronal culture model of acquired epilepsy, and altered calcium (Ca2+) homeostasis has been implicated in the development of SREDs. Using antisense oligonucleotides, this study was conducted to determine whether selective suppression of CaMK-II activity, with subsequent induction of SREDs, was associated with altered Ca2+ homeostasis in hippocampal neurons in culture. Antisense knockdown resulted in the development of SREDs and a decrease in both immunocytochemical staining and enzyme activity of CaMK-II. Evaluation of [Ca2+](i) using Fura indicators revealed that antisense-treated neurons manifested increased basal [Ca2+](i), whereas missense-treated neurons showed no change in basal [Ca2+](i). Antisense suppression of CaMK-II was also associated with an inability of neurons to restore a Ca2+ load. Upon removal of oligonucleotide treatment, CaMK-II suppression and Ca2+ homeostasis recovered to control levels and SREDs were abolished. To our knowledge, the results demonstrate the first evidence that selective suppression of CaMK-II activity results in alterations in Ca2+ homeostasis and the development of SREDs in hippocampal neurons and suggest that CaMK-II suppression may be causing epileptogenesis by altering Ca2+ homeostatic mechanisms.