Discovery of High‑Frequency Sarcomere Vibrations — Hyperthermal Sarcomeric Oscillations (HSOs) (BBRC, 2015)

Using neonatal rat cardiomyocytes, this study analyzed in detail how sarcomeres behave when a focused infrared laser locally raises the cell temperature to 38–42 °C. After heating, the sarcomeres began to oscillate autonomously at 5–10 Hz, independent of intracellular Ca²⁺ fluctuations. The authors named this phenomenon Hyperthermal Sarcomeric Oscillations (HSOs).

When the sarcoplasmic reticulum (SR) remained functional, HSOs coexisted with the ordinary excitation–contraction beat (~1 Hz), meaning each sarcomere simultaneously expressed two entirely different rhythms. Pharmacological inhibition of the SR enlarged HSO amplitude over time and slightly lowered their frequency. These findings suggest that mammalian cardiac sarcomeres harbor an intrinsic rhythm far faster than the sinoatrial pace whenever the temperature slightly exceeds physiological levels.

The HSOs reported here later became the experimental foundation for concepts such as Contraction Rhythm Homeostasis (CRH), Sarcomere Chaos with Changes in Calcium (S4C), and Chaordic Homeodynamics. The simple manipulation of temperature to perturb the cooperative on/off equilibrium of sarcomeres—and to shift from Ca²⁺‑dependent to Ca²⁺‑independent oscillations—has opened new avenues for hierarchical understanding of cardiac mechanics.