Mitochondrial permeability transition and calcium dynamics in striatal neurons upon intense NMDA receptor activation

Deregulation of the intracellular Ca2+ homeostasis by NMDA receptor activation leads to neuronal cell death. Induction of the mitochondrial permeability transition pore (MPT) by Ca2+ is a critical event in mediating cell death. In this study, we used fluorescent Ca2+ indicators to investigate the effect of high concentrations of NMDA on cytosolic and mitochondrial Ca2+ concentrations ([Ca2+](c) and [Ca2+](m), respectively) in cultured striatal neurons. Exposure to NMDA resulted in an immediate, sustained increase in [Ca2+](c) followed by a secondary increase in [Ca2+](c). This second increase of [Ca2+](c) was prevented by pretreatment with /V-methyl-valine-4-cyclosporin (NMV-Cys). Exposure of neurons to NMDA also resulted in an increase in [Ca2+](m) that was followed by a precipitous decrease in the rhod-2 signal. This decrease followed the time frame of the secondary increase in [Ca2+](c). Preincubation of the neurons with NMV-Cys prevented the decrease in rhod-2 fluorescence. These dynamic changes in the rhod-2 signal and [Ca2+](m) in response to NMDA were confirmed by using confocal microscopy. The presented results indicate that MPT can be detected in living neurons using fluorescent Ca2+ indicators, which would allow the study of the physiological role of MPT in cell death.