Neuronal-Specific Inhibition of Endoplasmic Reticulum Mg(2+)/Ca(2+) ATPase Ca(2+) Uptake in a Mixed Primary Hippocampal Culture Model of Status Epilepticus

Loss of intracellular calcium homeostasis is an established mechanism associated with neuronal dysfunction and status epilepticus. Sequestration of free cytosolic calcium into endoplasmic reticulum by Mg(2+)/Ca(2+) adenosinetriphosphatase (ATPase) is critical for maintenance of intracellular calcium homeostasis. Exposing hippocampal cultures to low-magnesium media is a well-accepted in vitro model of status epilepticus. Using this model, it was shown that endoplasmic reticulum Ca(2+) uptake was significantly inhibited in homogenates from cultures demonstrating electrophysiological seizure phenotypes. Calcium uptake was mainly neuronal. However, glial Ca(2+) uptake was also significantly inhibited. Viability of neurons exposed to low magnesium was similar to neurons exposed to control solutions. Finally, it was demonstrated that Ca(2+) uptake inhibition and intracellular free Ca(2+) levels increased in parallel with increasing incubation in low magnesium. The results suggest that inhibition of Mg(2+)/Ca(2+) ATPase-mediated endoplasmic reticulum Ca(2+) sequestration contributes to loss of intracellular Ca(2+) homeostasis associated with status epilepticus. This study describes for the first time inhibition of endoplasmic reticulum Mg(2+)/Ca(2+) ATPase in a mixed primary hippocampal model of status epilepticus. In combination with animal models of status epilepticus, the cell culture model provides a powerful tool to further elucidate mechanisms that result in inhibition of Mg(2+)/Ca(2+) ATPase and downstream consequences of decreased enzyme activity.