title: Mitochondrial inefficiencies and anoxic ATP hydrolysis capacities in diabetic rat heart.
abstract: As ~80% of diabetic patients die from heart failure, an understanding of diabetic cardiomyopathy is crucial. Mitochondria occupy 35-40% of the mammalian cardiomyocyte volume and supply 95% of the heart's ATP, and diabetic heart mitochondria show impaired structure, arrangement, and function. We predict that bioenergetic inefficiencies are present in diabetic heart mitochondria; therefore, we explored mitochondrial proton and electron handling by linking oxygen flux to steady-state ATP synthesis, reactive oxygen species (ROS) production, and mitochondrial membrane potential (ΔΨ) within rat heart tissues. Sprague-Dawley rats were injected with streptozotocin (STZ, 55 mg/kg) to induce type 1 diabetes or an equivalent volume of saline (control, n = 12) and fed standard rat chow for 8 wk. By coupling high-resolution respirometers with purpose-built fluorometers, we followed Magnesium Green (ATP synthesis), Amplex UltraRed (ROS production), and safranin-O (ΔΨ). Relative to control rats, the mass-specific respiration of STZ-diabetic hearts was depressed in oxidative phosphorylation (OXPHOS) states. Steady-state ATP synthesis capacity was almost one-third lower in STZ-diabetic heart, which, relative to oxygen flux, equates to an estimated 12% depression in OXPHOS efficiency. However, with anoxic transition, STZ-diabetic and control heart tissues showed similar ATP hydrolysis capacities through reversal of the F1F0-ATP synthase. STZ-diabetic cardiac mitochondria also produced more net ROS relative to oxygen flux (ROS/O) in OXPHOS. While ΔΨ did not differ between groups, the time to develop ΔΨ with the onset of OXPHOS was protracted in STZ-diabetic mitochondria. ROS/O is higher in lifelike OXPHOS states, and potential delays in the time to develop ΔΨ may delay ATP synthesis with interbeat fluctuations in ADP concentrations. Whereas diabetic cardiac mitochondria produce less ATP in normoxia, they consume as much ATP in anoxic infarct-like states.
authors.affiliation: School of Biological Sciences, University of Auckland, Auckland, New Zealand;
authors.forename: Toan
authors.initials: T
authors.lastname: Pham
authors.affiliation: Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand; and Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand.
authors.forename: Denis
authors.initials: D
authors.lastname: Loiselle
authors.affiliation: School of Biological Sciences, University of Auckland, Auckland, New Zealand;
authors.forename: Amelia
authors.initials: A
authors.lastname: Power
authors.affiliation: School of Biological Sciences, University of Auckland, Auckland, New Zealand; a.hickey@auckland.ac.nz.
authors.forename: Anthony J R
authors.initials: AJ
authors.lastname: Hickey
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D019069:Cell Respiration; D003921:Diabetes Mellitus, Experimental / Q000139:chemically induced / Q000150:complications / Q000378:metabolism; D003922:Diabetes Mellitus, Type 1 / Q000139:chemically induced / Q000150:complications / Q000378:metabolism; D058065:Diabetic Cardiomyopathies / Q000209:etiology / Q000378:metabolism*; D004734:Energy Metabolism; D006868:Hydrolysis; D000860:Hypoxia / Q000209:etiology / Q000378:metabolism*; D008297:Male; D053078:Membrane Potential, Mitochondrial; D008929:Mitochondria, Heart / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D010085:Oxidative Phosphorylation; D018384:Oxidative Stress; D006180:Proton-Translocating ATPases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013997:Time Factors
chemical_list: D017382:Reactive Oxygen Species; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases
keywords: ATP flux; mitochondrial efficiency; mitochondrial membrane potential; mitochondrial reactive oxygen species production