The textbook view holds that a rise in intracellular Ca²⁺ initiates contraction in both skeletal and cardiac muscle, yet recent work highlights temperature as an equally important regulator. This review synthesizes how small, physiological temperature shifts (~36–40 °C) bias the on–off equilibrium of thin filaments and thereby alter force generation and Ca²⁺ sensitivity.
The authors first survey two classical phenomena:
Rapid Cooling Contracture (RCC) and the chronic positive inotropy seen at low temperature, in which cooling primarily boosts force via changes in Ca²⁺ handling.
The opposite effect at higher temperatures—hyperthermic negative inotropy, where contractile force weakens.
Next, they discuss evidence that the troponin–tropomyosin complex partially detaches from actin as temperature rises, and that the Ca²⁺ affinity of troponin C increases with heat. Acting together, these changes enable Ca²⁺‑independent “thermal activation.” Indeed, a brief ~5 °C rise induced by an infrared laser shortens cardiomyocytes without a Ca²⁺ transient, and reconstituted thin filaments in in vitro motility assays begin to glide spontaneously near 37 °C. Such findings suggest that local heating could restore force in conditions with depressed Ca²⁺ sensitivity—e.g., dilated cardiomyopathy—without compromising energetic efficiency.
The final section considers differential heat sensitivities among sarcomeric proteins and the normal‑temperature variations across species (mouse, rabbit, human). It also looks ahead to “thermal inotropy” technologies that might use nano‑heaters or magnetic particles, outlining both potential and challenges.
Overall, the review vividly demonstrates that temperature is no longer a passive parameter but an active switch capable of modulating muscle contraction.