In order to determine the sequence of cellular processes in glutamate toxicity, we simultaneously recorded O2 consumption, cytosolic Ca2+ concentration ([Ca2+]i), and mitochondrial membrane potential (mδψ) in single cortical neurons. Oxygen consumption was measured using an amperometric self-referencing platinum electrode adjacent to neurons in which [Ca2+]i and mδψ were monitored with Fluo-4 and TMRE+, respectively, using a spinning disk laser confocal microscope. Excitotoxic doses of glutamate caused an elevation of [Ca2+]i followed seconds afterwards by an increase in O2 consumption which reached a maximum level within 1-5 min. A modest increase in mδψ occurred during this time period, and then, shortly before maximal O2 consumption was reached, the mδψ, as indicated by TMRE+ fluorescence, dissipated. Maximal O2 consumption lasted up to 5 min and then declined together with mδψ and ATP levels, while [Ca2+]i further increased. mδψ and [Ca2+]i returned to baseline levels when neurons were treated with an NMDA receptor antagonist shortly after the [Ca2+]i increased. Our unprecedented spatial and time resolution revealed that this sequence of events is identical in all neurons, albeit with considerable variability in magnitude and kinetics of changes in O2 consumption, [Ca2+]i, and mδψ. The data obtained using this new method are consistent with a model where Ca 2+ influx causes ATP depletion, despite maximal mitochondrial respiration, minutes after glutamate receptor activation.
- Oxygen consumption
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience