Mitochondrial deenergization underlies neuronal calcium overload following a prolonged glutamate challenge

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Abstract
The purpose of our work was to study the relationship between glutamate (GLU)‐induced mitochondrial depolarization and deterioration of neuronal Ca2+ homeostasis following a prolonged GLU challenge. The experiments were performed on cultured rat cerebellar granule cells using the fluorescent probes, rhodamine 123 and fura‐2. All the cells, in which 100 μM GLU ( 10 μM glycine, 0 Mg2+) induced only relatively slight mitochondrial depolarization (1.1‐1.3‐fold increase in rhodamine 123 fluorescence), retained their ability to recover [Ca2+]i following a prolonged GLU challenge. In contrast, the cells in which GLU treatment induced pronounced mitochondrial depolarization (2–4‐fold increase in rhodamine 123 fluorescence), exhibited a high Ca2+ plateau in the post‐glutamate period. Application of 3–5 mM NaCN or 0.25–1 μM FCCP during this Ca2+ plateau phase usually failed to produce a further noticeable increase in [Ca2+]1. Regression analysis revealed a good correlation (r 2 = 0.88 ± 0.03, n = 19) between the increase in the percentage of rhodamine 123 fluorescence and the postglutamate [Ca2+]i Collectively, the results obtained led us to conclude that the GLU‐induced neuronal Ca2+ overload was due to the collapse of the mitochondrial potential and subsequent ATP depletion.