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Giuseppe Calamita - One of the best experts on this subject based on the ideXlab platform.
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Water permeability of rat liver mitochondria: A biophysical study.
Biochimica et biophysica acta, 2006Co-Authors: Giuseppe Calamita, Patrizia Gena, Daniela Meleleo, Domenico Ferri, Maria SveltoAbstract:The movement of water accompanying solutes between the cytoplasm and the Mitochondrial spaces is central for Mitochondrial volume homeostasis, an important function for Mitochondrial activities and for preventing the deleterious effects of excess matrix swelling or contraction. While the discovery of aquaporin water channels in the Inner Mitochondrial Membrane provided valuable insights into the basis of Mitochondrial plasticity, questions regarding the identity of Mitochondrial water permeability and its regulatory mechanism remain open. Here, we use a stopped flow light scattering approach to define the water permeability and Arrhenius activation energy of the rat liver whole intact mitochondrion and its Membrane subcompartments. The water permeabilities of whole brain and testis mitochondria as well as liposome models of the lipid bilayer composing the liver Inner Mitochondrial Membrane are also characterized. Besides finding remarkably high water permeabilities for both mitochondria and their Membrane subcompartments, the existence of additional pathways of water movement other than aquaporins are suggested.
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The Inner Mitochondrial Membrane has aquaporin-8 water channels and is highly permeable to water.
Journal of Biological Chemistry, 2005Co-Authors: Giuseppe Calamita, Patrizia Gena, D. Ferri, G. Liquori, Annie Cavalier, Daniel Thomas, M. SveltoAbstract:Mitochondria are remarkably plastic organelles constantly changing their shape to fulfil their various functional activities. Although the osmotic movement of water into and out of the mitochondrion is central for its morphology and activity, the molecular mechanisms and the pathways for water transport across the Inner Mitochondrial Membrane (IMM), the main barrier for molecules moving into and out of the organelle, are completely unknown. Here, we show the presence of a member of the aquaporin family of water channels, AQP8, and demonstrate the strikingly high water permeability (Pf) characterizing the rat liver IMM. Immunoblotting, electron microscopy, and biophysical studies show that the largest mitochondria feature the highest AQP8 expression and IMM Pf. AQP8 was also found in the mitochondria of other organs, whereas no other known aquaporins were seen. The osmotic water transport of liver IMM was partially inhibited by the aquaporin blocker Hg2+, while the related activation energy remained low, suggesting the presence of a Hg2+-insensitive facilitated pathway in addition to AQP8. It is suggested that AQP8-mediated water transport may be particularly important for rapid expansions of Mitochondrial volume such as those occurring during active oxidative phosphorylation and those following apoptotic signals.
Claes B Wollheim - One of the best experts on this subject based on the ideXlab platform.
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matrix alkalinization a novel Mitochondrial signal for sustained pancreatic β cell activation
The EMBO Journal, 2009Co-Authors: Andreas Wiederkehr, Kyu Sang Park, Olivier Dupont, Nicolas Demaurex, Gary W Cline, Tullio Pozzan, Claes B WollheimAbstract:Nutrient secretagogues activate mitochondria of the pancreatic β‐cell through the provision of substrate, hyperpolarisation of the Inner Mitochondrial Membrane and Mitochondrial calcium rises. We report that Mitochondrial matrix pH, a parameter not previously studied in the β‐cell, also exerts an important control function in Mitochondrial metabolism. During nutrient stimulation matrix pH alkalinises, monitored by the Mitochondrial targeted fluorescent pH‐sensitive protein mtAlpHi or 31 P‐NMR inorganic phosphate chemical shifts following saturation transfer. Compared with other cell types, the resting Mitochondrial pH was surprisingly low, rising from pH 7.25 to 7.7 during nutrient stimulation of rat β‐cells. As cytosolic alkalinisation to the nutrient was of much smaller amplitude, the matrix alkalinisation was accompanied by a pronounced increase of the ΔpH across the Inner Mitochondrial Membrane. Furthermore, matrix alkalinisation closely correlates with the cytosolic ATP net increase, which is also associated with elevated ATP synthesis rates in mitochondria. Preventing ΔpH increases in permeabilised cells abrogated substrate‐driven ATP synthesis. We propose that the Mitochondrial pH and ΔpH are key determinants of Mitochondrial energy metabolism and metabolite transport important for cell activation.
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matrix alkalinization a novel Mitochondrial signal for sustained pancreatic β cell activation
The EMBO Journal, 2009Co-Authors: Andreas Wiederkehr, Kyu Sang Park, Olivier Dupont, Nicolas Demaurex, Gary W Cline, Tullio Pozzan, Claes B WollheimAbstract:Nutrient secretagogues activate mitochondria of the pancreatic beta-cell through the provision of substrate, hyperpolarisation of the Inner Mitochondrial Membrane and Mitochondrial calcium rises. We report that Mitochondrial matrix pH, a parameter not previously studied in the beta-cell, also exerts an important control function in Mitochondrial metabolism. During nutrient stimulation matrix pH alkalinises, monitored by the Mitochondrial targeted fluorescent pH-sensitive protein mtAlpHi or (31)P-NMR inorganic phosphate chemical shifts following saturation transfer. Compared with other cell types, the resting Mitochondrial pH was surprisingly low, rising from pH 7.25 to 7.7 during nutrient stimulation of rat beta-cells. As cytosolic alkalinisation to the nutrient was of much smaller amplitude, the matrix alkalinisation was accompanied by a pronounced increase of the DeltapH across the Inner Mitochondrial Membrane. Furthermore, matrix alkalinisation closely correlates with the cytosolic ATP net increase, which is also associated with elevated ATP synthesis rates in mitochondria. Preventing DeltapH increases in permeabilised cells abrogated substrate-driven ATP synthesis. We propose that the Mitochondrial pH and DeltapH are key determinants of Mitochondrial energy metabolism and metabolite transport important for cell activation.
Jean Velours - One of the best experts on this subject based on the ideXlab platform.
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is there a relationship between the supramolecular organization of the Mitochondrial atp synthase and the formation of cristae
Biochimica et Biophysica Acta, 2002Co-Authors: Mariefrance Giraud, Daniel Brèthes, Patrick Paumard, Jacques Vaillier, Jacques Schaeffer, Vincent Soubannier, Jean-paul Di Rago, Genevieve Arselin, Benedicte Salin, Jean VeloursAbstract:Blue native polyacrylamide gel electrophoresis (BN-PAGE) analyses of detergent Mitochondrial extracts have provided evidence that the yeast ATP synthase could form dimers. Cross-linking experiments performed on a modified version of the i-subunit of this enzyme indicate the existence of such ATP synthase dimers in the yeast Inner Mitochondrial Membrane. We also show that the first transMembrane segment of the eukaryotic b-subunit (bTM1), like the two supernumerary subunits e and g, is required for dimerization/oligomerization of ATP synthases. Unlike mitochondria of wild-type cells that display a well-developed cristae network, mitochondria of yeast cells devoid of subunits e, g ,o rbTM1 present morphological alterations with an abnormal proliferation of the Inner Mitochondrial Membrane. From these observations, we postulate that an anomalous organization of the Inner Mitochondrial Membrane occurs due to the absence of ATP synthase dimers/oligomers. We provide a model in which the Mitochondrial ATP synthase is a key element in cristae morphogenesis. D 2002 Elsevier Science B.V. All rights reserved.
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is there a relationship between the supramolecular organization of the Mitochondrial atp synthase and the formation of cristae
Biochimica et Biophysica Acta, 2002Co-Authors: Mariefrance Giraud, Daniel Brèthes, Patrick Paumard, Jacques Vaillier, Jacques Schaeffer, Vincent Soubannier, Jean-paul Di Rago, Genevieve Arselin, Benedicte Salin, Jean VeloursAbstract:Blue native polyacrylamide gel electrophoresis (BN-PAGE) analyses of detergent Mitochondrial extracts have provided evidence that the yeast ATP synthase could form dimers. Cross-linking experiments performed on a modified version of the i-subunit of this enzyme indicate the existence of such ATP synthase dimers in the yeast Inner Mitochondrial Membrane. We also show that the first transMembrane segment of the eukaryotic b-subunit (bTM1), like the two supernumerary subunits e and g, is required for dimerization/oligomerization of ATP synthases. Unlike mitochondria of wild-type cells that display a well-developed cristae network, mitochondria of yeast cells devoid of subunits e, g, or bTM1 present morphological alterations with an abnormal proliferation of the Inner Mitochondrial Membrane. From these observations, we postulate that an anomalous organization of the Inner Mitochondrial Membrane occurs due to the absence of ATP synthase dimers/oligomers. We provide a model in which the Mitochondrial ATP synthase is a key element in cristae morphogenesis.
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the atp synthase is involved in generating Mitochondrial cristae morphology
The EMBO Journal, 2002Co-Authors: Patrick Paumard, Daniel Brèthes, Jacques Vaillier, Benedicte Coulary, Jacques Schaeffer, Vincent Soubannier, David M Mueller, Jean-paul Di Rago, Jean VeloursAbstract:The Inner Membrane of the mitochondrion folds inwards, forming the cristae. This folding allows a greater amount of Membrane to be packed into the mitochondrion. The data in this study demonstrate that subunits e and g of the Mitochondrial ATP synthase are involved in generating Mitochondrial cristae morphology. These two subunits are non‐essential components of ATP synthase and are required for the dimerization and oligomerization of ATP synthase. Mitochondria of yeast cells deficient in either subunits e or g were found to have numerous digitations and onion‐like structures that correspond to an uncontrolled biogenesis and/or folding of the Inner Mitochondrial Membrane. The present data show that there is a link between dimerization of the Mitochondrial ATP synthase and cristae morphology. A model is proposed of the assembly of ATP synthase dimers, taking into account the oligomerization of the yeast enzyme and earlier data on the ultrastructure of Mitochondrial cristae, which suggests that the association of ATP synthase dimers is involved in the control of the biogenesis of the Inner Mitochondrial Membrane.
Patrizia Gena - One of the best experts on this subject based on the ideXlab platform.
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Water permeability of rat liver mitochondria: A biophysical study.
Biochimica et biophysica acta, 2006Co-Authors: Giuseppe Calamita, Patrizia Gena, Daniela Meleleo, Domenico Ferri, Maria SveltoAbstract:The movement of water accompanying solutes between the cytoplasm and the Mitochondrial spaces is central for Mitochondrial volume homeostasis, an important function for Mitochondrial activities and for preventing the deleterious effects of excess matrix swelling or contraction. While the discovery of aquaporin water channels in the Inner Mitochondrial Membrane provided valuable insights into the basis of Mitochondrial plasticity, questions regarding the identity of Mitochondrial water permeability and its regulatory mechanism remain open. Here, we use a stopped flow light scattering approach to define the water permeability and Arrhenius activation energy of the rat liver whole intact mitochondrion and its Membrane subcompartments. The water permeabilities of whole brain and testis mitochondria as well as liposome models of the lipid bilayer composing the liver Inner Mitochondrial Membrane are also characterized. Besides finding remarkably high water permeabilities for both mitochondria and their Membrane subcompartments, the existence of additional pathways of water movement other than aquaporins are suggested.
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The Inner Mitochondrial Membrane has aquaporin-8 water channels and is highly permeable to water.
Journal of Biological Chemistry, 2005Co-Authors: Giuseppe Calamita, Patrizia Gena, D. Ferri, G. Liquori, Annie Cavalier, Daniel Thomas, M. SveltoAbstract:Mitochondria are remarkably plastic organelles constantly changing their shape to fulfil their various functional activities. Although the osmotic movement of water into and out of the mitochondrion is central for its morphology and activity, the molecular mechanisms and the pathways for water transport across the Inner Mitochondrial Membrane (IMM), the main barrier for molecules moving into and out of the organelle, are completely unknown. Here, we show the presence of a member of the aquaporin family of water channels, AQP8, and demonstrate the strikingly high water permeability (Pf) characterizing the rat liver IMM. Immunoblotting, electron microscopy, and biophysical studies show that the largest mitochondria feature the highest AQP8 expression and IMM Pf. AQP8 was also found in the mitochondria of other organs, whereas no other known aquaporins were seen. The osmotic water transport of liver IMM was partially inhibited by the aquaporin blocker Hg2+, while the related activation energy remained low, suggesting the presence of a Hg2+-insensitive facilitated pathway in addition to AQP8. It is suggested that AQP8-mediated water transport may be particularly important for rapid expansions of Mitochondrial volume such as those occurring during active oxidative phosphorylation and those following apoptotic signals.
Alan Cahill - One of the best experts on this subject based on the ideXlab platform.
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a ca2 induced Mitochondrial permeability transition causes complete release of rat liver endonuclease g activity from its exclusive location within the Mitochondrial interMembrane space identification of a novel endo exonuclease activity residing wit
Nucleic Acids Research, 2003Co-Authors: Adrian Davies, Stuart H. Hershman, Gabriel J. Stabley, Jan B. Hoek, Jason Peterson, Alan CahillAbstract:Endonuclease G, a protein historically thought to be involved in Mitochondrial DNA (mtDNA) replication, repair, recombination and degradation, has recently been reported to be involved in nuclear DNA degradation during the apoptotic process. As a result, its involvement in mtDNA homeostasis has been called into question and has necessitated detailed analyses of its precise location within the mitochondrion. Data is presented localizing rat liver endonuclease G activity exclusively to the Mitochondrial interMembrane space with no activity associated with either the interior face of the Inner Mitochondrial Membrane or with the Mitochondrial matrix. Additionally, it is shown that endonuclease G can be selectively released from the mitochondrion via induction of a Ca2+-induced Mitochondrial permeability transition and that, upon its release, a further nuclease activity loosely associated with the interior face of the Inner Mitochondrial Membrane and distinct in its properties from that of endonuclease G can be detected.