title: Regulation of excitation-contraction coupling in mouse cardiac myocytes: integrative analysis with mathematical modelling.
abstract: BACKGROUND
  The cardiomyocyte is a prime example of inherently complex biological system with inter- and cross-connected feedback loops in signalling, forming the basic properties of intracellular homeostasis. Functional properties of cells and tissues have been studied e.g. with powerful tools of genetic engineering, combined with extensive experimentation. While this approach provides accurate information about the physiology at the endpoint, complementary methods, such as mathematical modelling, can provide more detailed information about the processes that have lead to the endpoint phenotype.
  
  
  RESULTS
  In order to gain novel mechanistic information of the excitation-contraction coupling in normal myocytes and to analyze sophisticated genetically engineered heart models, we have built a mathematical model of a mouse ventricular myocyte. In addition to the fundamental components of membrane excitation, calcium signalling and contraction, our integrated model includes the calcium-calmodulin-dependent enzyme cascade and the regulation it imposes on the proteins involved in excitation-contraction coupling. With the model, we investigate the effects of three genetic modifications that interfere with calcium signalling: 1) ablation of phospholamban, 2) disruption of the regulation of L-type calcium channels by calcium-calmodulin-dependent kinase II (CaMK) and 3) overexpression of CaMK. We show that the key features of the experimental phenotypes involve physiological compensatory and autoregulatory mechanisms that bring the system to a state closer to the original wild-type phenotype in all transgenic models. A drastic phenotype was found when the genetic modification disrupts the regulatory signalling system itself, i.e. the CaMK overexpression model.
  
  
  CONCLUSIONS
  The novel features of the presented cardiomyocyte model enable accurate description of excitation-contraction coupling. The model is thus an applicable tool for further studies of both normal and defective cellular physiology. We propose that integrative modelling as in the present work is a valuable complement to experiments in understanding the causality within complex biological systems such as cardiac myocytes.
authors.affiliation: Department of Physics, University of Oulu & Biocenter Oulu, Finland. jussi.koivumaki@oulu.fi
authors.forename: Jussi T
authors.initials: JT
authors.lastname: Koivumäki
authors.forename: Topi
authors.initials: T
authors.lastname: Korhonen
authors.forename: Jouni
authors.initials: J
authors.lastname: Takalo
authors.forename: Matti
authors.initials: M
authors.lastname: Weckström
authors.forename: Pasi
authors.initials: P
authors.lastname: Tavi
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000502:physiology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D020746:Calcium Channels, L-Type; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium