Heart cells are prone to self-organization
Last reviewed: 16.10.2021
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In the heart, some cells periodically lose the ability to conduct an impulse. In order not to disturb the cardiac activity, cardiomyocytes are able to form a separate branched conducting system.
Cardiomyocytes are responsible for the contractile function of the heart. We are talking about special cells that can generate and pass through themselves electrical impulses. However, in addition to these structures, heart tissue is represented by connective tissue cells that do not transmit an excitation wave - for example, fibroblasts.
Normally, fibroblasts retain the structural framework of the heart and take part in the healing of damaged tissue sites. With a heart attack and other injuries and diseases, part of the cardiomyocytes die: their cells are filled with fibroblasts, by the type of tissue scarring. With a large accumulation of fibroblasts, the passage of an electric wave worsens: this condition is called cardiofibrosis in cardiology.
Cells that are unable to conduct an impulse block the normal activity of the heart. As a result, the wave is directed to bypass the obstacle, which can lead to a circulatory path of excitation: a rotational spiral wave is formed. This condition is referred to as a reverse impulse course - this is the so-called re-entry, which provokes the development of cardiac arrhythmias.
Most likely, high-density fibroblasts cause the formation of a reverse impulse course for the following reasons:
- non-conducting cells have a heterogeneous structure;
- A large number of formed fibroblasts are a kind of labyrinth for wave flows that are forced to follow a longer and curved path.
The peak density of fibroblast structures is called the percolation threshold. This indicator is calculated using the theory of percolation, a mathematical method for assessing the appearance of structural bonds. Conducting and non-conducting cardiomyocytes are currently becoming such bonds.
According to scientists, heart tissue should lose the possibility of conduction with an increase in the number of fibroblasts by 40%. Remarkably, in practice, conductivity is observed even in the case of an increase in the number of non-conducting cells by 70%. This phenomenon is associated with the ability of cardiomyocytes to self-organize.
According to scientists, conducting cells organize their own cytoskeleton inside the fibrous tissue in such a way that they can enter into common syncytium with other heart tissues. Experts estimated the passage of an electric pulse in 25 connective tissue samples having a different percentage level of conductive and non-conductive structures. As a result, the percolation peak was calculated at 75%. At the same time, scientists noticed that cardiomyocytes were not arranged in a chaotic order, but were organized into a branching conducting system. To date, researchers continue their work on the project: they are faced with the goal of creating new methods for eliminating arrhythmias, which will be based on information obtained during the experiments.
Details of the work can be found on the page journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1006597