A transient inhibition of mitochondrial ATP synthesis by nitric oxide synthase activation triggered apoptosis in primary cortical neurons

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Abstract
In order to investigate the relationship between nitric oxide‐mediated regulation of mitochondrial function and excitotoxicity, the role of mitochondrial ATP synthesis and intracellular redox status on the mode of neuronal cell death was studied. Brief (5 min) glutamate (100 µm) receptor stimulation in primary cortical neurons collapsed the mitochondrial membrane potential (Δψm) and transiently (30 min) inhibited mitochondrial ATP synthesis, causing early (1 h) necrosis or delayed (24 h) apoptosis. The transient inhibition of ATP synthesis was paralleled to a loss of NADH, which was fully recovered shortly after the insult. In contrast, NADPH and the GSH/GSSG ratio were maintained, but progressively decreased thereafter. Twenty‐four hours after glutamate treatment, ATP was depleted, a phenomenon associated with a persistent inhibition of mitochondrial succinate–cytochrome c reductase activity and delayed necrosis. Blockade of either nitric oxide synthase (NOS) activity or the mitochondrial permeability transition (MPT) pore prevented Δψm collapse, the transient inhibition of mitochondrial ATP synthesis, early necrosis and delayed apoptosis. However, blockade of NOS activity, but not the MPT pore, prevented the inhibition of succinate–cytochrome c reductase activity and delayed ATP depletion and necrosis. From these results, we suggest that glutamate receptor‐mediated NOS activation would trigger MPT pore opening and transient inhibition of ATP synthesis leading to apoptosis in a neuronal subpopulation, whereas other groups of neurons would undergo oxidative stress and persistent inhibition of ATP synthesis leading to necrosis.