Stimulation of H₂O₂ generation by calcium in brain mitochondria respiring on α‐glycerophosphate

Abstract

It has been reported recently (Tretter et al., 2007b) that in isolated guinea pig brain mitochondria supported by alpha-glycerophosphate (alpha-GP) reactive oxygen species (ROS) are produced through the reverse electron transport (RET) in the respiratory chain and by alpha-glycerophosphate dehydrogenase (alpha-GPDH). We studied the effect of calcium on the generation of H(2)O(2) as measured by the Amplex Red fluorescent assay in this model. H(2)O(2) production in alpha-GP-supported mitochondria was increased significantly in the presence of 100, 250, and 500 nM Ca(2+), respectively. In addition, Ca(2+) enhanced the membrane potential, the rate of oxygen consumption, and the NAD(P)H autofluorescence in these mitochondria. Direct measurement of alpha-GPDH activity showed that Ca(2+) stimulated the enzyme by decreasing the Km for alpha-GP. In those mitochondria where RET was eliminated by the Complex I inhibitor rotenone (2 microM) or due to depolarization by ADP (1 mM), the rate of H(2)O(2) formation was smaller and the stimulation of H(2)O(2) generation by Ca(2+) was prevented partly, but the stimulatory effect of Ca(2+) was still significant. These data indicate that in alpha-GP-supported mitochondria activation of alpha-GPDH by Ca(2+) leads to an accelerated RET-mediated ROS generation as well as to a stimulated ROS production by alpha-GPDH.

Novel Inhibitors of Mitochondrial sn-Glycerol 3-phosphate Dehydrogenase

“…However, because of a lack of cell-permeant selective inhibitors of mGPDH and compensation by other NAD + regenerating mechanisms, there is a lack of evidence of functional mGPDH activity in intact systems. We tested the role of mGPDH-dependent metabolism using iGP-1 in synaptosomes because mGPDH is active in neurons [27], [45], [46], there is a significant role for NADH shuttles in synaptic energetics [26], [47], there are no reports on neural function in mGPDH −/− mice, and synaptosomes are a tractable intact system for studying neuronal energetics under tightly controlled cell-, substrate-, and demand-specific conditions.…”

Changes to mitochondrial ultrastructure in optic nerve vulnerable to secondary degeneration in vivo are limited by irradiation at 670 nm

“…A similar scenario could be responsible for a restoration of axonal mitochondrial profiles to normal size by day 1 in the current model and the increasingly elliptical shape of mitochondria in axons compared to normal at day 1. However, it is also possible that mitochondrial size was simply maintained and/or increased via a protective effect due to increased cytochrome c oxidase activity, as has been reported with R/NIR-IT [23,24], prevention of reverse electron transport and maintenance of the mitochondrial permeability transition [7,46] or restoration of normal osmotic conditions. R/NIR-IT also prevented the shift towards more elliptical mitochondrial profiles that was observed in glia at day 1 and 7 in ON vulnerable to secondary degeneration.…”

Calcium and Mitochondrial Reactive Oxygen Species Generation: How to Read the Facts

“…It has to be noted here that submicromolar concentrations of Ca 2+ stimulate ROS production by mitochondrial α -glycerophosphate dehydrogenase [112] likely due to stimulation of the enzyme described earlier in liver mitochondria [113], which might be significant in vivo in deenergized mitochondria, which are unable to take up Ca 2+ and to control the cytosolic Ca 2+ concentration.…”