Phase-targeting rapid cryofixation of perfused rat hearts demonstrated that mean sarcomere length was significantly shorter during peak systole (1.57 µm) than during diastole (1.93 µm).
Phase-targeting rapid cryofixation successfully visualizes precise spatiotemporal changes and inhomogeneities in sarcomere length across different cardiac phases in the beating rat heart.
Absolute Event Rate: 1.57% vs 1.93%
Abstract The heart is a functional syncytium consisting of numerous cardiomyocytes that repetitively exhibit coordinated contractions/relaxations. However, the extent to which myocyte sarcomere arrangements in the heart differ across beats is unknown. To examine this, we conducted cardiac phase-targeting rapid cryofixation of Langendorff-perfused rat hearts. We adjusted the timepoint of cryogen exposure to the electrically paced heart and observed phase-dependent differences in the sarcomere length (SL) of subepicardial myocytes by α-actinin immunohistochemistry, namely a significantly shorter SL during systole than during diastole. We detected spatially inhomogeneous SL distributions by generating a heatmap of the myocardium. For peak systole the SL heatmap exhibited nearly uniform SL shortening within and among the individual myocytes with some myocardia exhibiting nonuniform SLs. During diastole, the heart showed predominant SL elongation, which was also accompanied by patchy distributions of locally short-SL regions, reflecting inhomogeneous SLs. This SL inhomogeneity was attenuated by pharmacological relaxation by 2,3-butanedione monoxime. The heatmap of the rapidly-frozen heart during ventricular fibrillation also revealed inhomogeneous SLs within and among individual myocytes. Overall, cardiac phase-targeting cryofixation unveiled in-depth behaviors on SL in the heart. Our cryofixation strategy will open a new horizon to clarify precise spatiotemporal changes in sarcomere structures and understand cardiac functions.
Tamura et al. (Sat,) conducted a other in Healthy (animal model) (n=25). Phase-targeting rapid cryofixation during systole vs. Phase-targeting rapid cryofixation during diastole was evaluated on Mean sarcomere length (µm). Phase-targeting rapid cryofixation of perfused rat hearts demonstrated that mean sarcomere length was significantly shorter during peak systole (1.57 µm) than during diastole (1.93 µm).