NMDA receptor stimulation in the absence of extracellular Ca 2+ potentiates Ca 2+ influx-dependent cell death system

Abstract

The meaning of Ca 2+ influx in the time course of glutamate stimulation of neuronal cells was addressed. We demonstrated that Ca 2+ influx did not work straightforward in the determination of the fate of neuronal cells. There appears to be a critical period for Ca 2+ influx to work efficiently in glutamate-induced neuronal cell death. When Ca 2+ influx for 5 min from the beginning of glutamate stimulation was allowed in the whole stimulation period for 15 min, potent neuronal cell death could not be attained. On the other hand, when neuronal cells had been pre-treated with glutamate or NMDA for 5–10 min in the absence of extracellular Ca 2+ following Ca 2+ influx for 5 min fully induced neuronal cell death. APV inhibited this pre-treatment effect. It appears that the pre-treatment of neuronal cells with glutamate or NMDA in the absence of extracellular Ca 2+ promotes the Ca 2+ influx-dependent process executing cell death. The pre-treatment itself did not change the pattern of intracellular Ca 2+ elevation by the activation of NMDA receptors. These results imply that glutamate activation of NMDA receptors consists of two different categories of pathways relating to neuronal cell death, i.e., Ca 2+ influx independent and dependent, and that the former facilitates the latter to drive neuronal cells to death. This study clarified a mechanism by which glutamate quickly determines cell fate.