Edit Publication: Saks 2000 Acta Physiol Scand

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Abstract:	The mechanism of metabolic regulation of mitochondrial respiration in cardiac muscle cells was studied experimentally in the permeabilized heart fibres of mice and by computer modelling in silico. The experiments showed that the rate of mitochondrial respiration could be controlled by local production of ADP by mitochondrial creatine kinase in the intermembrane space of mitochondria. The spatially inhomogenous reaction–diffusion model of compartmentalized energy transfer was used to analyse which metabolite level in cytoplasm may be important for regulation of respiration. At low and moderate workloads, up to VO<sub>2</sub> equal to 70 μmol min<sup>-1</sup>g<sup>-1</sup> dry weight, the only factor to which respiration responded was inorganic phosphate. At the values of VO<sub>2</sub> higher than 70 μmol min<sup>-1</sup>g<sup>-1</sup> dry weight, the respiration rate responded mostly to changes in creatine, phosphocreatine and then time-averaged (over the contractile cycle) ADP concentrations in the cytoplasm. These results are taken to show that under conditions of moderate workloads, creatine kinase activity at given physiological creatine and phosphocreatine concentrations (apparent maximal activity achievable under these conditions) is in excess to oxidative phosphorylation rate, which is controlled by Pi concentration changes starting from very low values of the latter. At higher workloads mi-CK should be upregulated by increasing creatine and decreasing phosphocreatine concentrations, and only at very high workloads the ADP diffusion flux should be increased to upregulate oxidative phosphorylation. Thus, on the basis of the study in silico of compartmentalized energy transfer by phophocreatine/creatine system, the authors conclude that there exist multiple parallel regulatory factors controlling the rate of oxygen consumption in dependence of the workload. If creatine kinase is inhibited (and there is no myokinase activity), respiration requires high diffusive flux of ADP back into mitochondria, which is the sole regulator of respiration. This needs, however, increased ADP concentrations in the cytoplasm, which in turn result in inhibition of contraction.
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MiPareas:	Gender Respiration Instruments;methods mt-Biogenesis;mt-density mt-Structure;fission;fusion mt-Membrane mtDNA;mt-genetics nDNA;cell genetics Genetic knockout;overexpression Comparative MiP;environmental MiP Developmental biology Exercise physiology;nutrition;life style mt-Medicine Patients Pharmacology;toxicology mt-Awareness
Pathological states:	COPD Aging;senescence Alzheimer's Autism Cancer Cardiovascular Diabetes Inherited Infectious Myopathy Neurodegenerative Obesity Parkinson's Sepsis Other
Stress conditions:	Hypoxia Cell death Cryopreservation Ischemia-reperfusion Permeability transition Oxidative stress;RONS Temperature Mitochondrial disease
Organism:	Pig Human Mouse Rat Guinea pig Bovines Horse Dog Rabbit Cat Other mammals Chicken Zebrafish Drosophila Artemia Caenorhabditis elegans Saccharomyces cerevisiae Birds Reptiles Amphibians Fishes Chelicerates Crustaceans Hexapods Myriapods Annelids Molluscs Nematodes Other invertebrates Fungi Plants Protists Eubacteria Archea Algae
Tissues;cells:	Fat Heart Skeletal muscle Nervous system Liver Kidney Lung;gill Islet cell;pancreas;thymus Endothelial;epithelial;mesothelial cell Blood cells Genital Other cell lines CHO HEK HeLa Neuroblastoma Fibroblast HUVEC Macrophage-derived Lymphocyte Platelet Stem cells
Preparations:	SMP Intact organism Intact organ Permeabilized cells Permeabilized tissue Homogenate Isolated mitochondria Chloroplasts Enzyme Oxidase;biochemical oxidation Intact cells
Enzyme:	Complex I Adenine nucleotide translocase Complex II;succinate dehydrogenase Complex III Complex IV;cytochrome c oxidase Complex V;ATP synthase Inner mt-membrane transporter Marker enzyme Supercomplex TCA cycle and matrix dehydrogenases Uncoupling protein
Regulation; kinetics:	pH Aerobic glycolysis ADP ATP ATP production AMP Calcium Coupling efficiency;uncoupling Cyt c Flux control Inhibitor Ion;substrate transport mt-Membrane potential Oxygen kinetics PCr;Cr Phosphate Redox state Substrate Temperature Threshold;excess capacity Uncoupler Fatty acid Amino acid Q-junction effect
Coupling:	ET LEAK ROUTINE OXPHOS
Pathways:	F N S Gp DQ CIV NS Other combinations ROX
High-resolution respirometry:	pH Oxygraph-2k TIP2k O2k-Fluorometer NO TPP Ca O2k-Spectrophotometer O2k-Manual O2k-Protocol Theory NextGen-O2k
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