| 1. |
- Covey-Crump, Elizabeth M, et al.
(författare)
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Temperature-dependent changes in respiration rates and redox poise of the ubiquinone pool in protoplasts and isolated mitochondria of potato leaves
- 2007
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 129, s. 175-184
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Tidskriftsartikel (refereegranskat)abstract
- In many environments, leaves experience large diurnal variations in temperature. Such short-term changes in temperature are likely to have important implications for respiratory metabolism in leaves. Here, we used intact leaf, protoplasts and isolated mitochondria to determine the impact of short-term changes in temperature on respiration rates (R), adenylate concentrations and the redox poise of the ubiquinone (UQ) pool in mitochondria of potato leaves. The Q10 (i.e. proportional change in R for each 10°C rise in temperature) of respiration was 1.8, both for intact leaves and protoplasts. In protoplasts, the redox poise of the extracted UQ pool (UQR/UQT) increased from 0.33 at 22°C, to 0.76 at 15°C. Further decreases in temperature (from 15 to 5°C) resulted in UQR/UQT decreasing to 0.40. Adenylate ratios in protoplasts were also temperature dependent. At high adenosine 5'-triphosphate (ATP) adenosine 5'-diphosphate (ADP) ratios (i.e. low ADP concentrations), UQR/UQT values were low, suggesting that adenylates restricted flux via the UQ-reducing pathways more than they restricted flux via pathways that oxidized UQH2. To assess whether high rates of alternative oxidase (AOX) activity could have uncoupled respiratory flux (and thus UQR/UQT) from adenylate restriction of the cytochrome (Cyt) pathway, we constructed kinetic curves of O2 uptake (via the two pathways) vs UQR/UQT in isolated mitochondria, measured at two temperatures (15 and 25°C); measurements were made for mitochondria operating under state 3 (i.e. +ADP) and state 4 (i.e. −ADP) conditions. In contrast to the Cyt pathway, flux via the AOX was temperature insensitive, with maximal rates of AOX activity representing 21–57% of total O2 uptake in isolated mitochondria. We conclude that temperature-dependent variations in UQR/UQT are largely dependent on temperature-dependent changes in adenylate ratios, and that flux via the AOX could in some circumstances help reduce maximal UQ values.
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| 2. |
- Kabra, Uma D, et al.
(författare)
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Direct Substrate Delivery into Mitochondrial-Fission Deficient Pancreatic Islets Rescues Insulin Secretion
- 2017
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 66:5, s. 1247-1257
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Tidskriftsartikel (refereegranskat)abstract
- In pancreatic beta cells, mitochondrial bioenergetics control glucose-stimulated insulin secretion (GSIS). Mitochondrial dynamics are generally associated with quality control, maintaining the functionality of bioenergetics. By acute pharmacological inhibition of mitochondrial fission protein Drp1, we here demonstrate that mitochondrial fission is necessary for GSIS in mouse and human islets. We confirm that genetic silencing of Drp1 increases mitochondrial proton leak in MIN6 cells. However, our comprehensive analysis of pancreatic islet bioenergetics reveals that Drp1 does not control insulin secretion via its effect on proton leak but instead via modulation of glucose-fuelled respiration. Notably, pyruvate fully rescues the impaired insulin secretion of fission-deficient beta cells, demonstrating that defective mitochondrial dynamics solely impact substrate supply upstream of oxidative phosphorylation. The present findings provide novel insights in how mitochondrial dysfunction may cause pancreatic beta cell failure. In addition, the results will stimulate new thinking in the intersecting fields of mitochondrial dynamics and bioenergetics, as treatment of defective dynamics in mitochondrial diseases appears to be possible by improving metabolism upstream of mitochondria.
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| 3. |
- Kabra, Uma D., et al.
(författare)
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Respiratory Parameters for the Classification of Dysfunctional Insulin Secretion by Pancreatic Islets
- 2021
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Ingår i: Metabolites. - : MDPI AG. - 2218-1989 .- 2218-1989. ; 11:6
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Tidskriftsartikel (refereegranskat)abstract
- The development of obesity and type 2 diabetes (T2D) has been associated with impaired mitochondrial function. In pancreatic beta (beta) cells, mitochondrial energy metabolism plays a central role in triggering and controlling glucose-stimulated insulin secretion (GSIS). Here, we have explored whether mitochondrial bioenergetic parameters assessed with Seahorse extracellular flux technology can quantitatively predict insulin secretion. We metabolically stressed male C57BL/6 mice by high-fat feeding (HFD) and measured the glucose sensitivity of islet respiration and insulin secretion. The diet-induced obese (DIO) mice developed hyperinsulinemia, but no pathological secretory differences were apparent between isolated DIO and chow islets. Real-time extracellular flux analysis, however, revealed a lower respiratory sensitivity to glucose in DIO islets. Correlation of insulin secretion with respiratory parameters uncovers compromised insulin secretion in DIO islets by oxidative power. Normalization to increased insulin contents during DIO improves the quantitative relation between GSIS and respiration, allowing to classify dysfunctional properties of pancreatic insulin secretion, and thereby serving as valuable biomarker for pancreatic islet glucose responsiveness and health.
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