Glutamate induces H2O2 synthesis in nonsynaptic brain mitochondria.

Mitochondrial reactive oxygen species regulate many important biological processes. We studied H2O2 formation by nonsynaptic brain mitochondria in response to the addition of low concentrations of glutamate, an excitatory neurotransmitter. We demonstrated that glutamate at concentrations from 10 to 50 µM stimulated the H2O2 generation in mitochondria up to 4-fold, in a dose-dependent manner. The effect of glutamate was observed only in the presence of Ca(2+) (20 µM) in the incubation medium, and the rate of calcium uptake by the brain mitochondria was increased by up to 50% by glutamate. Glutamate-dependent effects were sensitive to the NMDA receptor inhibitors MK-801 (10 µM) and D-AP5 (20 µM) and the inhibitory neurotransmitter glycine (5mM). We have shown that the H2O2 formation caused by glutamate is associated with complex II and is dependent on the mitochondrial potential. We have found that nonsynaptic brain mitochondria are a target of direct glutamate signaling, which can specifically activate H2O2 formation through mitochondrial respiratory chain complex II. The H2O2 formation induced by glutamate can be blocked by glycine, an inhibitory neurotransmitter that prevents the deleterious effects of glutamate in brain mitochondria.

Mechanism underlying the protective effect of glycine in energetic disturbances in brain tissues under hypoxic conditions.

Glycine stabilizes energetics of brain mitochondria under conditions of brain hypoxia in vivo modeled by ligation of the common carotid artery in rats. Hypoxia reduced respiratory control in brain cortex mitochondria from 7.7 ± 0.5 to 4.5 ± 0.3. Preliminary oral administration of glycine almost completely prevented this decrease. In both in vitro models of hypoxia, similar phosphorylation disturbances were detected in both cortical slices and isolated brain mitochondria; they were effectively prevented by glycine. Hypoxia activates H(2)O(2) generation in mitochondrial suspension. The process is significantly reduced in the presence of 5 mM glycine. It is concluded that both in the model of hypoxia in vivo and during in vitro modeling of hypoxia in cortical slices and mitochondria, glycine acts as a protector inhibiting generation of reactive oxygen species in mitochondria and preventing energetics disturbances in brain mitochondria.