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

In order to investigate the relationship between nitric oxide-mediated regu lation of mitochondrial function and excitotoxicity, the role of mitochondr ial ATP synthesis and intracellular redox status on the mode of neuronal ce ll death was studied. Brief (5 min) glutamate (100 muM) receptor stimulatio n in primary cortical neurons collapsed the mitochondrial membrane potentia l (Delta psi (m)) and transiently (30 min) inhibited mitochondrial ATP synt hesis, causing early (1 h) necrosis or delayed (24 h) apoptosis. The transi ent 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/G SSG ratio were maintained, but progressively decreased thereafter. Twenty-f our hours after glutamate treatment, ATP was depleted, a phenomenon associa ted with a persistent inhibition of mitochondrial succinate-cytochrome c re ductase activity and delayed necrosis. Blockade of either nitric oxide synt hase (NOS) activity or the mitochondrial permeability transition (MPT) pore prevented Delta psi (m) collapse, the transient inhibition of mitochondria l 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. Fro m these results, we suggest that glutamate receptor-mediated NOS activation would trigger MPT pore opening and transient inhibition of ATP synthesis l eading to apoptosis in a neuronal subpopulation, whereas other groups of ne urons would undergo oxidative stress and persistent inhibition of ATP synth esis leading to necrosis.