Transmurally Harmonized Cardiac Crossbridge Formation during Contraction

Abstract

Background: Because of the thickness and the three-dimensionally complex structures of the left ventricle (LV), it has been difficult to observe how crossbridge dynamics correlate with LV performance in a beating heart preparation using a second-generation synchrotron radiation. Recently we confirmed the possibility to observe the transmural crossbridge (CB) dynamics (CBD) by analyzing the reflection of the beating LV free wall associated with transmural variations of regional myofilament orientations using a third generation synchrotron facility. Purpose: To reveal transmural difference of crossbridge dynamics in the beating LV. Methods: We paced isolated crystalloid perfused isovolumically beating rat hearts (n=5) at 2Hz. We recorded x-ray diffraction images of LV epimyocardial and midmyocardial regions at SPring-8 with LV pressure (LVP) and analyzed transmural CBD utilizing transmural variations of regional myofilament orientations. Results: During contraction, normalized LVP and transmural CBDs temporally harmonized well each other. However during relaxation, the CB decay of midmyocardium was faster, but that of epimyocardium later than LVP. Conclusion: The transmural CBD and LVP development well harmonized temporally during systole while their decay during diastole disaccord with each other. [Jpn J Physiol 54 Suppl:S103 (2004)]