Natalja Jepihhina

Heterogeneity of Diffusion Restrictions in Cardiomyocytes

Abstract

In a healthy heart, energy supply and demand should be in balance. This is achieved by efficient transport of high-energy phosphates. Researchers studying heart muscle cells, cardiomyocytes, however, discovered that the diffusion of adenine nucleotide molecules is restricted in heart muscle cells. Interestingly, diffusion restriction diminishes in ischemic heart cells, implying that the mechanisms of diffusion restriction are important for maintaining the normal functioning of the heart and heart muscle cells. Thus, it is crucial to understand the origin of diffusion obstacles in cardiomyocytes.

This thesis is part of a project studying diffusion restrictions in adult rat cardiomyocytes. The main goal of this thesis was to understand whether the diffusion of adenine nucleotides is restricted in a single heart muscle cell and, if so, to evaluate the distribution of diffusion restrictions. The novelty of the approach is conducting experiments at the single-cell level, whereas previous reports were based on cell-population studies. The advantage of such an approach is the ability to distinguish intracellular diffusion obstacles from overall diffusion restrictions in the system. This was achieved through measurements of the kinetics of cell respiration using autofluorescence-based methods.

The work conducted in this thesis showed that diffusion restrictions in cardiomyocytes exist at the single-cell level. This was shown in adult rat cardiomyocytes and confirmed in cardiomyocytes of wild-type and creatine-deficient mice. The combination of experimental data and mathematical modeling made it possible to conclude that diffusion obstacles found in cardiomyocytes are caused by two distinct features: closing of voltage-dependent anion channels (VDACs) on the mitochondrial outer membrane (MOM) and barriers in the cell cytoplasm, which both contribute equally to diffusion restrictions. Specifically, it was found that 98% of the VDACs on the MOM were not available for adenosine phosphate transport and thus restricted its diffusion.

The findings presented in the current thesis enhance our insight into the distribution of diffusion restrictions in cardiomyocytes. Since diffusion restrictions influence the transport of molecules from the cytosol to mitochondria and are therefore one of the factors that determine cell fate, a better understanding of their regulatory mechanisms may help to develop new treatments for diseased hearts.

Supervisors

  • Supervisor: Marko Vendelin

Opponents

  • Prof. Anders Arner, PhD; Karolinska, Sweden

  • Prof. Allen Kaasik, PhD; University of Tartu, Estonia

Time of defense

15 September 2017 at 11:00 in the Institute of Cybernetics, room B101

Thesis

You can download the PDF of the thesis at https://digi.lib.ttu.ee/i/?8085.