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* Laboratory of Fundamental and Applied Bioenergetics, INSERM E0221, Joseph Fourier University, Grenoble, France; 
Laboratory of Bioenergetics, National Institute of Chemical Physics and Biophysics, Tallinn, Estonia; 
Department of Transplant Surgery, University Hospital Innsbruck, Innsbruck, Austria; 
A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia; ¶ RFMQ-TIMC Laboratory, UMR 5525 CNRS, Institute Albert Bonniot, Grenoble, France; and || Institute of Cybernetics, Tallinn, Estonia
Correspondence: Address reprint requests to V. A. Saks, Laboratory of Bioenergetics, Joseph Fourier University, 2280 Rue de la Piscine, BP53X-38041, Grenoble Cedex 9, France. Tel.: 33-47-663-5627; E-mail: Valdur.Saks{at}ujf-grenoble.fr.
Heterogeneity of ADP diffusion and regulation of respiration were studied in permeabilized cardiomyocytes and cardiac fibers in situ and in silico. Regular arrangement of mitochondria in cells was altered by short-time treatment with trypsin and visualized by confocal microscopy. Manipulation of matrix volumes by changing K+ and sucrose concentrations did not affect the affinity for ADP either in isolated heart mitochondria or in skinned fibers. Pyruvate kinase (PK)-phosphoenolpyruvate (PEP) were used to trap ADP generated in Ca,MgATPase reactions. Inhibition of respiration by PK-PEP increased 2–3 times after disorganization of regular mitochondrial arrangement in cells. ADP produced locally in the mitochondrial creatine kinase reaction was not accessible to PK-PEP in intact permeabilized fibers, but some part of it was released from mitochondria after short proteolysis due to increased permeability of outer mitochondrial membrane. In in silico studies we show by mathematical modeling that these results can be explained by heterogeneity of ADP diffusion due to its restrictions at the outer mitochondrial membrane and in close areas, which is changed after proteolysis. Localized restrictions and heterogeneity of ADP diffusion demonstrate the importance of mitochondrial functional complexes with sarcoplasmic reticulum and myofibrillar structures and creatine kinase in regulation of oxidative phosphorylation.
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