Fig. 1 (IMAGE)
Caption
Hierarchical structure of muscle and activation of thin filaments. In both skeletal and cardiac muscles under a relaxed state, a low intracellular calcium ion concentration is maintained and the tropomyosin-troponin complex suppresses interaction between molecular motor myosin and actin filament (F-actin); this is termed the OFF state. Upon an increase in the intracellular calcium ion concentration, or by calcium signaling, the binding of calcium ion to troponin leads to the displacement of tropomyosin. The conformational change of the thin filaments allows myosin to interact with actin, and active force is generated; this is termed the ON state. Heat works as “thermal signaling,” inducing an ON state even in the absence of calcium ions.
Credit
Shuya Ishii, Kotaro Oyama and Madoka Suzuki
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