title: ADP compartmentation analysis reveals coupling between pyruvate kinase and ATPases in heart muscle.
abstract: Cardiomyocytes have intracellular diffusion restrictions, which spatially compartmentalize ADP and ATP. However, the models that predict diffusion restrictions have used data sets generated in rat heart permeabilized fibers, where diffusion distances may be heterogeneous. This is avoided by using isolated, permeabilized cardiomyocytes. The aim of this work was to analyze the intracellular diffusion of ATP and ADP in rat permeabilized cardiomyocytes. To do this, we measured respiration rate, ATPase rate, and ADP concentration in the surrounding solution. The data were analyzed using mathematical models that reflect different levels of cell compartmentalization. In agreement with previous studies, we found significant diffusion restriction by the mitochondrial outer membrane and confirmed a functional coupling between mitochondria and a fraction of ATPases in the cell. In addition, our experimental data show that considerable activity of endogenous pyruvate kinase (PK) remains in the cardiomyocytes after permeabilization. A fraction of ATPases were inactive without ATP feedback by this endogenous PK. When analyzing the data, we were able to reproduce the measurements only with the mathematical models that include a tight coupling between the fraction of endogenous PK and ATPases. To our knowledge, this is the first time such a strong coupling of PK to ATPases has been demonstrated in permeabilized cardiomyocytes.
authors.affiliation: Laboratory of Systems Biology, Institute of Cybernetics, Tallinn University of Technology, Tallinn, Estonia.
authors.forename: Mervi
authors.initials: M
authors.lastname: Sepp
authors.forename: Marko
authors.initials: M
authors.lastname: Vendelin
authors.forename: Heiki
authors.initials: H
authors.lastname: Vija
authors.forename: Rikke
authors.initials: R
authors.lastname: Birkedal
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002451:Cell Compartmentation; D019069:Cell Respiration; D004058:Diffusion; D004735:Energy Transfer; D005260:Female; D042541:Intracellular Space / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D008954:Models, Biological; D009119:Muscle Contraction; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000201:enzymology* / Q000378:metabolism; D010539:Permeability; D021381:Protein Transport; D011770:Pyruvate Kinase / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000244:Adenosine Diphosphate; D011770:Pyruvate Kinase; D000251:Adenosine Triphosphatases; D002118:Calcium