In vitro status epilepticus causes sustained elevation of intracellular calcium levels in hippocampal neurons

Abstract

Calcium ions and calcium-dependent systems have been implicated in the pathophysiology of status epilepticus (SE). However, the dynamics of intracellular calcium ([Ca 2+] i) levels during SE has not yet been studied. We have employed the hippocampal neuronal culture (HNC) model of in vitro SE that produces continuous epileptiform discharges to study spatial and dynamic changes in [Ca 2+] i levels utilizing confocal laser scanning microscopy and the calcium binding dye, indo-1. During SE, the average [Ca 2+] i levels increased from control levels of 150–200 nM to levels of 450–600 nM. This increased [Ca 2+] i was maintained for the duration of SE. Following SE, [Ca 2+] i levels gradually returned to basal values. The duration of SE was shown to affect the ability of the neuron to restore resting [Ca 2+] i levels. Both N-methyl- d-aspartate (NMDA) receptor-gated and voltage-gated Ca 2+ channels (VGCCs) contributed to the increased calcium entry during SE. Moreover, this elevation in [Ca 2+] i occurred in both the nucleus and cytosol. These results provide the first dynamic measurement of [Ca 2+] i during prolonged electrographic seizure discharges in an in vitro SE model and suggest that prolonged epileptiform discharges give rise to abnormal sustained increases in [Ca 2+] i levels that may play a role in the neuronal cell damage and long-term plasticity changes associated with SE.