Heterogeneity of Diffusion Restrictions in Cardiomyocytes

ABSTRACT

In a healthy heart, the energy supply and demand should be in balance. This is achieved by an efficient transport of high energy phosphates. The researchers of heart muscle cells, cardiomyocytes, however, discovered that the diffusion of adenine nucleotide molecules is restricted in the heart muscle cells. Interestingly enough, the diffusion restriction diminishes in the ischemic heart cells, implying that the mechanisms of the diffusion restrictions are important to maintain 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 a part of the 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 used approach is making experiments at the single cell level, whereas previous reports were based on cell population studies. The advantage of such approach is the ability to distinguish intracellular diffusion obstacles from overall diffusion restrictions in the system. This was achieved by 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 on adult rat cardiomyocytes and confirmed on cardiomyocytes of wild type and creatine deficient mice. Combination of experimental data and mathematical modeling made it possible to conclude that restricting 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 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 the diffusion restrictions influence the transport of molecules from the cytosol to mitochondria and, hence, are one of the factors that determine the cell fate, better understanding of their regulatory mechanisms may help to develop new treatments for diseased hearts.

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 PDF of the thesis here