Decylubiquinone increases mitochondrial function in synaptosomes

Abstract

The effects of decylubiquinone, a ubiquinone analogue, on mitochondrial function and inhibition thresholds of the electron transport chain enzyme complexes in synaptosomes were investigated. Decylubiquinone increased complex I/III and complex II/III activities by 64 and 80%, respectively, and attenuated reductions in oxygen consumption at high concentrations of the complex III inhibitor myxothiazol. During inhibition of complex I, decylubiquinone attenuated reductions in synaptosomal oxygen respiration rates, as seen in the complex I inhibition threshold. Decylubiquinone increased the inhibition thresholds of complex I/III, complex II/III, and complex III over oxygen consumption in the nerve terminal by 25-50%, when myxothiazol was used to inhibit complex III. These results imply that decylubiquinone increases mitochondrial function in the nerve terminal during complex I or III inhibition. The potential benefits of decylubiquinone in diseases where complex I, I/III, II/III, or III activities are deficient are discussed.

FIGURE 1.

Decylubiquinone increases the activities of complexes I/III and II/III in synaptosomes. Rat brain synaptosomes were incubated with ethanol (C) or 50 μm decylubiquinone (DQ) in Krebs buffer at 37 °C for 5 min. The activities of complex I (nmol/min/mg) (a), complex I/III (nmol/min/mg) (b), complex II/III (nmol/min/mg) (c), complex III (k/min/mg) (d), and complex IV (k/min/mg) (e) in the samples were determined by spectrophotometry. Experiments were performed on at least three individual preparations and results are expressed as mean ± S.E. (error bars). Significant differences between the decylubiquinone-treated sample and the corresponding control are shown by ** for p < 0.01 and *** for p < 0.001.

FIGURE 2.

Decylubiquinone does not alter oxygen consumption rates in synaptosomes during rotenone titration. Rat brain synaptosomes were incubated with a series of concentrations of rotenone (0–10 μm) in the absence (■) and presence (□) of 50 μm decylubiquinone in Krebs buffer at 37 °C, and rates of oxygen consumption were recorded and plotted against rotenone concentrations. Experiments were performed on at least three individual preparations, and results are expressed as mean ± S.E. (error bars).

FIGURE 3.

Decylubiquinone attenuates myxothiazol-induced reduction in oxygen consumption rates in synaptosomes. Rat brain synaptosomes were incubated with a series of concentrations of myxothiazol (0–1 μm) in the absence (■) and presence (□) of 50 μm decylubiquinone in Krebs buffer at 37 °C, and rates of oxygen consumption were recorded and plotted against myxothiazol concentrations. Experiments were performed on at least three individual preparations, and results are expressed as mean ± S.E. (error bars). Significant differences between the decylubiquinone-treated and untreated samples are shown by ** for p < 0.01 and *** for p < 0.001.

FIGURE 4.

Decylubiquinone attenuates antimycin A-induced reduction in oxygen consumption rates in synaptosomes. Rat brain synaptosomes were incubated with a series of concentrations of antimycin A (0–500 nm) in the absence (■) and presence (□) of 50 μm decylubiquinone in Krebs buffer at 37 °C and rates of oxygen consumption were recorded and plotted against antimycin A concentrations. Experiments were performed on at least three individual preparations, and results are expressed as mean ± S.E. (error bars). Significant differences between the decylubiquinone-treated and untreated samples are shown by *** for p < 0.001.

FIGURE 5.

Decylubiquinone partially attenuates rotenone-induced reduction in oxygen consumption in synaptosomes. Rat brain synaptosomes were incubated with a series of concentrations of rotenone (0–10 μm) in the absence and presence of 50 μm decylubiquinone in Krebs buffer in an oxygen electrode at 37 °C. Rates of oxygen consumption and corresponding complex I activity were determined and expressed as percentages of their controls and used to generate the complex I inhibition threshold curves in the absence (●) and presence (○) of decylubiquinone. The control rates of complex I activity in the absence and presence of decylubiquinone were 40.6 ± 5.6 nmol/min/mg and 38.4 ± 4.3 nmol/min/mg, respectively. Experiments were performed on five individual preparations, and results are expressed as mean ± S.E. (error bars).

FIGURE 6.

Decylubiquinone does not alter complex I/III inhibition threshold in synaptosomes when titrated with rotenone. Rat brain synaptosomes were incubated with a series of concentrations of rotenone (0–10 μm) in the absence and presence of 50 μm decylubiquinone in Krebs buffer in an oxygen electrode at 37 °C. Rates of oxygen consumption and corresponding complex I/III activity were determined and expressed as percentages of their controls and used to generate the complex I/III inhibition threshold curves in the absence (●) and presence (○) of decylubiquinone. The control rates of complex I/III activity in the absence and presence of decylubiquinone were 53 ± 6.6 nmol/min/mg and 79.5 ± 9.2 nmol/min/mg, respectively. Experiments were performed on five individual preparations, and results are expressed as mean ± S.E. (error bars).

FIGURE 7.

Decylubiquinone increases complex I/III inhibition threshold in synaptosomes, when titrated with myxothiazol. Rat brain synaptosomes were incubated with a series of concentrations of myxothiazol (0–1 μm) in the absence and presence of 50 μm decylubiquinone in Krebs buffer in an oxygen electrode at 37 °C. Rates of oxygen consumption and corresponding complex I/III activity were determined and expressed as percentages of their controls and used to generate the complex I/III inhibition threshold curves in the absence (●) and presence (○) of decylubiquinone. The control rates of complex I/III activity in the absence and presence of decylubiquinone were 44.2 ± 4.8 nmol/min/mg and 73.8 ± 8.25 nmol/min/mg, respectively. Experiments were performed on five individual preparations, and results are expressed as mean ± S.E. (error bars).

FIGURE 8.

Decylubiquinone increases complex II/III inhibition threshold in synaptosomes. Rat brain synaptosomes were incubated with a series of concentrations of myxothiazol (0–1 μm) in the absence and presence of 50 μm decylubiquinone in Krebs buffer in an oxygen electrode at 37 °C. Rates of oxygen consumption and corresponding complex II/III activity were determined and expressed as percentages of their controls and used to generate the complex II/III inhibition threshold curves in the absence (●) and presence (○) of decylubiquinone. The control rates of complex II/III activity in the absence and presence of decylubiquinone were 33.9 ± 2.5 nmol/min/mg and 64.4 ± 5.8 nmol/min/mg, respectively. Experiments were performed on five individual preparations, and results are expressed as mean ± S.E. (error bars).

FIGURE 9.

Decylubiquinone increases complex III inhibition threshold in synaptosomes. Rat brain synaptosomes were incubated with a series of concentrations of myxothiazol (0–1 μm) in the absence and presence of 50 μm decylubiquinone in Krebs buffer in an oxygen electrode at 37 °C. Rates of oxygen consumption and corresponding complex III activity were determined and expressed as percentages of their controls and used to generate the complex III inhibition threshold curves in the absence (●) and presence (○) of decylubiquinone. The control rates of complex I activity in the absence and presence of decylubiquinone were 2.72 ± 0.34 k/min/mg and 2.72 ± 0.39 k/min/mg, respectively. Experiments were performed on five individual preparations, and results are expressed as mean ± S.E. (error bars).