Restricted ADP movement in cardiomyocytes: Cytosolic diffusion obstacles are complemented with a small number of open mitochondrial voltage-dependent anion channels.
Adequate intracellular energy transfer is crucial for proper cardiac function. In energy starved failing hearts, partial restoration of energy transfer can rescue mechanical performance. There are two types of diffusion obstacles that interfere with energy transfer from mitochondria to ATPases: mitochondrial outer membrane (MOM) with voltage-dependent anion channel (VDAC) permeable to small hydrophilic molecules and cytoplasmatic diffusion barriers grouping ATP-producers and -consumers. So far, there is no method developed to clearly distinguish the contributions of cytoplasmatic barriers and MOM to the overall diffusion restriction. Furthermore, the number of open VDACs in vivo remains unknown. The aim of this work was to establish the partitioning of intracellular diffusion obstacles in cardiomyocytes. We studied the response of mitochondrial oxidative phosphorylation of permeabilized rat cardiomyocytes to changes in extracellular ADP by recording 3D image stacks of NADH autofluorescence. Using cell-specific mathematical models, we determined the permeability of MOM and cytoplasmatic barriers. We found that only ~2% of VDACs are accessible to cytosolic ADP and cytoplasmatic diffusion barriers reduce the apparent diffusion coefficient by 6-10×. In cardiomyocytes, diffusion barriers in the cytoplasm and by the MOM restrict ADP/ATP diffusion to similar extents suggesting a major role of both barriers in energy transfer and other intracellular processes.
Laboratory of Systems Biology, Institute of Cybernetics, Tallinn University of Technology, Akadeemia Rd 21, 12618 Tallinn, Estonia.
Päivo
P
Simson
Laboratory of Systems Biology, Institute of Cybernetics, Tallinn University of Technology, Akadeemia Rd 21, 12618 Tallinn, Estonia.
Natalja
N
Jepihhina
Laboratory of Systems Biology, Institute of Cybernetics, Tallinn University of Technology, Akadeemia Rd 21, 12618 Tallinn, Estonia.
Martin
M
Laasmaa
Laboratory of Systems Biology, Institute of Cybernetics, Tallinn University of Technology, Akadeemia Rd 21, 12618 Tallinn, Estonia.
Pearu
P
Peterson
Laboratory of Systems Biology, Institute of Cybernetics, Tallinn University of Technology, Akadeemia Rd 21, 12618 Tallinn, Estonia.
Rikke
R
Birkedal
Laboratory of Systems Biology, Institute of Cybernetics, Tallinn University of Technology, Akadeemia Rd 21, 12618 Tallinn, Estonia. Electronic address: markov@ioc.ee.
Marko
M
Vendelin
D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D003600:Cytosol / Q000378:metabolism; D004058:Diffusion; D008929:Mitochondria, Heart / Q000378:metabolism*; D008954:Models, Biological; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010539:Permeability; D051381:Rats; D050994:Voltage-Dependent Anion Channels / Q000378:metabolism*
D050994:Voltage-Dependent Anion Channels; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate
Intracellular diffusion obstacles; Oxidative phosphorylation; Rat cardiomyocytes; Regulation; Voltage-dependent anion channel VDAC