The force-generation process in active muscle is strain sensitive and endothermic: a temperature-perturbation study

Area of Science:

• Muscle physiology
• Biophysics
• Skeletal muscle mechanics

Background:

• Muscle contraction involves cross-bridge cycling between actin and myosin filaments.
• The mechanical properties of muscle fibers are temperature-sensitive.
• Understanding the energetics of cross-bridge force generation is key to muscle function.

Purpose of the Study:

• To investigate the tension decline during ramp shortening in skinned muscle fibers.
• To determine the temperature sensitivity of this tension decline.
• To elucidate the energetic nature of cross-bridge force generation.

Main Methods:

• Experiments on skinned rabbit psoas muscle fibers.
• Application of ramp shortening at various velocities.
• Rapid temperature jumps (T-jumps) to assess thermal sensitivity.
• Analysis of tension decline kinetics and force enhancement.

Main Results:

• Tension decline during ramp shortening exhibits distinct phases (P1 and P2 transitions).
• Shortening velocity affects the timing and magnitude of the P1 transition.
• Temperature jumps induce force enhancement, with the rate increasing linearly with velocity.
• The observed force enhancement and tension decline changes suggest an endothermic process.

Conclusions:

• The strain-sensitive cross-bridge force generation is an endothermic process.
• Temperature sensitivity plays a significant role in muscle force dynamics.
• These findings offer critical insights into the energetics of muscle contraction.