Abstract
The finding that upon neuronal activation glutamate is transported postsynaptically from synaptic clefts and increased lactate availability for neurons suggest that brain mitochondria (BM) utilize a mixture of substrates, namely pyruvate, glutamate, and the tricarboxylic acid cycle metabolites. We studied how glutamate affected oxidative phosphorylation and reactive oxygen species (ROS) production in rat BM oxidizing pyruvate + malate or succinate. Simultaneous oxidation of glutamate + pyruvate + malate increased state 3 and uncoupled respiration by 52 and 71%, respectively. The state 4 ROS generation increased 100% over BM oxidizing pyruvate + malate and 900% over that of BM oxidizing glutamate + malate. Up to 70% of ROS generation was associated with reverse electron transport. These effects of pyruvate + glutamate + malate were observed only with BM and not with liver or heart mitochondria. The effects of glutamate + pyruvate on succinate-supported respiration and ROS generation were not organ-specific and depended only on whether mitochondria were isolated with or without bovine serum albumin. With the non-bovine serum albumin brain and heart mitochondria oxidizing succinate, the addition of pyruvate and glutamate abrogated inhibition of Complex II by oxaloacetate. We conclude that (i) during neuronal activation, simultaneous oxidation of glutamate + pyruvate temporarily enhances neuronal mitochondrial ATP production, and (ii) intrinsic inhibition of Complex II by oxaloacetate is an inherent mechanism that protects against ROS generation during reverse electron transport.
Highlights
It has emerged that mitochondrial dysfunctions play an important role in the pathogenesis of degenerative diseases of the central nervous system (1–3)
They concluded that mitochondria are the major source of reactive oxygen species (ROS) and that at least 50% of ROS generated by brain mitochondria was associated with succinate-supported reverse electron transport (RET)
We suggested that the organization of the respiratory chain complexes into supercomplexes that occurs in brain mitochondria (BM) (9) may represent one of the intrinsic mechanisms to prevent excessive ROS generation (10)
Summary
Showed inhibition of succinate dehydrogenase (Complex II) with practically normal rates of glutamate ϩ malate oxidation (35), we analyzed interactions between substrates using non-BSA-BM. Data Acquisition—Data acquisition was performed using malate was present, the rate of state 4 declined somewhat, hardware and software from C&L Co. Chemicals—Sucrose, mannitol, and other chemicals were tion by 43% (p Ͻ 0.001) (Fig. 2A). Unpaired t test, and comparisons between more than two When BM oxidized pyruvate ϩ glutamate ϩ malate, the rate groups were made by analyses of variance followed by post hoc of oxidative phosphorylation (state 3) increased by 52%
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