Study of the Expression Transition of Cardiac Myosin Using Polarization-Dependent SHG Microscopy

Detection of the transition between the two myosin isoforms alpha- and beta-myosin in living cardiomyocytes is essential for understanding cardiac physiology and pathology. In this study, the differences in symmetry of polarization spectra obtained from alpha- and beta-myosin in various mammalian ventricles and propylthiouracil-treated rats are explored through polarization-dependent second harmonic generation microscopy. Here, we report for the, to our knowledge, first time that alpha- and beta-myosin, as protein crystals, possess different symmetries: the former has C6 symmetry, and the latter has C3v. A single-sarcomere line scan further demonstrated that the differences in polarization-spectrum symmetry between alpha- and beta-myosin came from their head regions: the head and neck domains of alpha- and beta-myosin account for the differences in symmetry. In addition, the dynamic transition of the polarization spectrum from C6 to C3v line profile was observed in a cell culture in which norepinephrine induced an alpha- to beta-myosin transition.