Fluorescence imaging of the living heart for understanding the basis of arrhythmias

Abstract

Recent outstanding progress in microscopic imaging technology and the advent of fluorescent probes have enabled us to visualize high spatiotemporal dynamics of intracellular molecules in living tissues. Here I introduce our research outcomes on functional fluorescence imaging of the heart especially for understanding the pathogenesis of cardiac arrhythmias. On the in situ Ca2+ imaging of perfused rat heart by rapid-scanning confocal microscopy, we found that burst emergence of intracellular Ca2+ waves evokes arrhythmogenic triggered activity and subsequent oscillatory depolarizations via the Na+-Ca2+ exchanger. Besides, impairment of Ca2+ release from the sarcoplasmic reticulum leads to emergence of Ca2+ waves and spatiotemporally inhomogeneous Ca2+ dynamics on systole, resulting in beat-to-beat Ca2+ alternans. Such alternating behaviors of Ca2+ dynamics are partly due to poor development of the transverse tubules, which are identified in murine atria and failing ventricular myocytes. In addition, impairment of the gap junctional communication via connexin 43 induced by dominant negative inhibition of neonatal rat ventricular myocyte monolayers results in generation of spiral wave reentry, suggesting the pivotal role of intercellular communications in genesis of arrhythmias. Furthermore, alterations in atrial histoanatomy, e.g., density and arrangements of myocytes and distribution of Cx43, could provide intrinsic arrhythmogenic bases of atrial fibrillation, which was revealed by combined optical imaging of the atria and precise histoanatomical examinations. In combination, fluorescence imaging of the living organisms provides indispensable information for unveiling functions and disease states.