Increased cardiac myosin super-relaxation as an energy saving mechanism in hibernating grizzly bears

Aim: The aim of the present study was to define whether cardiac myosin contributes to energy conservation in the heart of hibernating mammals. Methods: Thin cardiac strips were isolated from the left ventricles of active and hibernating grizzly bears; and subjected to loaded Mant-ATP chase assays, X-ray diffraction and proteomics. Main findings: Hibernating grizzly bears displayed an unusually high proportion of ATP-conserving super-relaxed cardiac myosin molecules that are likely due to altered levels of phosphorylation and rod region stability. Conclusions: Cardiac myosin depresses the heart's energetic demand during hibernation by modulating its function.