Microscopic heat pulses activate cardiac thin filaments.

Area of Science:

• Cardiovascular Physiology
• Muscle Contraction Biophysics
• Biochemical Kinetics

Background:

• Cardiac excitation-contraction coupling involves thin filament activation.
• Temperature influences the kinetics of actomyosin ATPase activity.
• Understanding temperature effects on cardiac muscle is crucial for physiological insights.

Purpose of the Study:

• To investigate the impact of rapid temperature increases on cardiac thin filament sliding.
• To quantify the temperature dependence of thin filament velocity in an in vitro motility assay.
• To explore the implications of these findings for cardiac muscle function at physiological temperatures.

Main Methods:

• Utilized focused infrared (IR) laser irradiation for rapid heating of reconstituted thin filaments.
• Employed an in vitro motility assay with human α-tropomyosin and bovine ventricular troponin.
• Measured temperature with high precision using rhodamine-phalloidin-labeled F-actin and a fluorescent thermosensor.

Main Results:

• Infrared laser irradiation induced thin filament sliding, with velocity increasing with temperature (25°C to ~46°C).
• Heating accelerated sliding in both the absence and presence of Ca²⁺ and ATP.
• The temperature dependence of sliding was less pronounced when Ca²⁺ was present.

Conclusions:

• Rapid heating enhances cardiac thin filament sliding velocity.
• Temperature plays a significant role in regulating the dynamics of cardiac thin filaments.
• Findings suggest a diastolic shift towards the 'on' state at physiological temperatures, facilitating systolic function.