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The warmed myocardium creates a contractile rhythm that combines stability and instability
Seine A. Shintani1

When the cultured rat cardiomyocytes are warmed to the core body temperature, the sarcomere inside the myocardium becomes Hyperthermal Sarcomeric Oscillations (HSOs), which repeats contraction and relaxation. When cultured cardiomyocytes undergo a spontaneous pulsation of approximately 1 Hz due to calcium-induced calcium release, HSOs have a contractile rhythm that combines chaotic instability with homeostatic stability. While the oscillation amplitude of HSOs fluctuates chaotically, the oscillation period is kept constant (Contraction Rhythm Homeostasis), and the oscillation waveform can be changed in response to changes in calcium concentration. It is thought that this property is born by the following mechanism. The chaotic change in synchronization between adjacent sarcomere in cardiomyocytes causes the average tension of the sarcomere population to be proportional to the change in intracellular calcium concentration. As a result, even if the total number of myosin molecules forming the cross bridge changes, the force applied to one myosin molecule will be kept constant. The properties of these HSOs are thought to be important for the heart, which pumped blood throughout the body during systole, to rapidly dilate the ventricles in the early stages of subsequent diastole.

Hyperthermal sarcomeric oscillations generated in warmed cardiomyocytes control amplitudes with chaotic properties while keeping cycles constant., Seine A. Shintani, Biochemical and Biophysical Research Communications, 611, 8-13, 2022.

<Figure Legends> A. Schematic diagram of the structure of sarcomere. B. Changes in the length of adjacent five consecutive sarcomere segments in cardiomyocytes. When the cardiomyocytes are warmed at the timing of the red arrow, HSOs become apparent. C. Spatio-temporal change in phase of HSOs during heating. On the black horizontal line corresponding to each sarcomere, the phase changes periodically. However, the phase relationship between adjacent sarcomere is changing flexibly. It repeats irregularly in the anti-phase synchronization state like the area surrounded by the white frame, and in the synchronization state like the area not surrounded by the white frame.

1. Department of Biomedical Sciences, College of Life and Health Sciences, Chubu University