PT - JOURNAL ARTICLE AU - Manus W. Ward AU - A. Cristina Rego AU - Bruno G. Frenguelli AU - David G. Nicholls TI - Mitochondrial Membrane Potential and Glutamate Excitotoxicity in Cultured Cerebellar Granule Cells AID - 10.1523/JNEUROSCI.20-19-07208.2000 DP - 2000 Oct 01 TA - The Journal of Neuroscience PG - 7208--7219 VI - 20 IP - 19 4099 - http://www.jneurosci.org/content/20/19/7208.short 4100 - http://www.jneurosci.org/content/20/19/7208.full SO - J. Neurosci.2000 Oct 01; 20 AB - The relationship between changes in mitochondrial membrane potential (Δψm) and the failure of cytoplasmic Ca2+ homeostasis, delayed Ca2+deregulation (DCD), is investigated for cultured rat cerebellar granule cells exposed to glutamate. To interpret the single-cell fluorescence response of cells loaded with tetramethylrhodamine methyl ester (TMRM+) or rhodamine-123, we devised and validated a mathematical simulation with well characterized effectors of Δψm and plasma membrane potential (ΔψP). Glutamate usually caused an immediate decrease in Δψm of <10 mV, attributable to Ca2+ accumulation rather than enhanced ATP demand, and these cells continued to generate ATP by oxidative phosphorylation until DCD. Cells for which the mitochondria showed a larger initial depolarization deregulated more rapidly. The mitochondria in a subpopulation of glutamate-exposed cells that failed to extrude Ca2+ that was released from the matrix after protonophore addition were bioenergetically competent. The onset of DCD during continuous glutamate exposure in the presence or absence of oligomycin was associated with a slowly developing mitochondrial depolarization, but cause and effect could not be established readily. In contrast, the slowly developing mitochondrial depolarization after transient NMDA receptor activation occurs before cytoplasmic free Ca2+([Ca2+]c) has risen to the set point at which mitochondria retain Ca2+. In the presence of oligomycin no increase in [Ca2+]c occurs during this depolarization. We conclude that transient Ca2+loading of mitochondria as a consequence of NMDA receptor activation initiates oxidative damage to both plasma membrane Ca2+ extrusion pathways and the inhibition of mitochondrial respiration. Depending on experimental conditions, one of these factors becomes rate-limiting and precipitates DCD.