Myosin-based regulation of the heartbeat at body temperature and physiological stimulation frequency

The heart is constantly beating at the body core temperature (37°C), adjusting its output to the changing needs of everyday life. We recently exploited time-resolved USAXS and SAXS at ID021 to measure the structural dynamics of the molecular myosin motors in different regions of the thick filament during the unitary mechanical response elicited by electrical pacing at 1 Hz of intact cardiac trabeculae at constant length at 27°C. Now the smaller beam and higher brightness available at ID02 after EBS combined with the new Eiger2-4M detector allow us to characterise the dynamics of the regulatory structural changes in the thick filament in thin cardiac trabeculae isolated from rat hearts for the first time at physiological temperature and pacing frequency, with faster kinetics of force development and relaxation.