Pacing-Induced Non-Uniform Ca²⁺ Dynamics in Rat Atria Revealed by Rapid-Scanning Confocal Microscopy

Abstract

Intracellular Ca2+ ([Ca2+]i) dynamics in isolated myocytes differ between the atria and ventricles due to the distinct t-tubular distributions. Although cellular aspects of ventricular [Ca2+]i dynamics in the heart have been extensively studied, little is known about those of atrial myocytes in situ. Here we visualized precise [Ca2+]i dynamics of atrial myocytes in Langendorff-perfused rat hearts by rapid-scanning confocal microscopy. Of 16 fluo-4-loaded hearts imaged during pacing up to 4-Hz, five hearts showed spatially uniform Ca2+ transients on systole among individual cells, whereas no discernible [Ca2+]i elevation developed during diastole. In contrast, the remaining hearts showed non-uniform [Ca2+]i dynamics within and among the cells especially under high-frequency (4 Hz) excitation, where subcellular cluster-like [Ca2+]i rises or wave-like [Ca2+]i propagation occurred on excitation. Such [Ca2+]i inhomogeneity was more pronounced at high-frequency pacing, showing beat-to-beat Ca2+ transient alternans. Despite such non-uniform dynamics, cessation of burst pacing of the atria was not followed by emergence of spontaneous Ca2+ waves, indicating minor Ca2+-releasing potentials of the sarcoplasmic reticulum (SR). In summary, rat atria display a propensity to show non-uniform [Ca2+]i dynamics on systole due to impaired Ca2+-release from the SR and paucity of t-tubules. Our results provide an important basis for understanding atrial pathophysiology.

Label-free detection of myocardial ischaemia in the perfused rat heart by spontaneous Raman spectroscopy

“…TMRE fluorescence imaging was performed in three hearts each for the SI and the IPC group, respectively. Minute morphological changes of cardiomyocytes were observed by confocal fluorescence images of the membrane dye, Di-4-ANEPPS (50 μM; Life Technologies), loaded by 5-min perfusion of the heart under immersion in the solution (n = 3) 29 30 .…”

Towards an integrated understanding of cardiac arrhythmogenesis − Growing roles of experimental pathology

“…As a result, atrial myocytes are more likely to exhibit non‐uniform [Ca 2+ ] i dynamics (Fig. S4C) during relatively high‐frequency beatings and, of great interest, [Ca 2+ ] i dynamics in the overall atrial regions show Ca 2+ alternans in the rat heart . This indicates that atrial myocytes with poor expression of T tubular networks may exhibit inhomogeneous contractions and thereby disturb electrical conduction, analogously to the ventricular myocytes in heart failure or under metabolic inhibitions .…”

“…S4C) during relatively high-frequency beatings and, of great interest, [Ca 2þ ] i dynamics in the overall atrial regions show Ca 2þ alternans in the rat heart. 12 This indicates that atrial myocytes with poor expression of T tubular networks may exhibit inhomogeneous contractions and thereby disturb electrical conduction, analogously to the ventricular myocytes in heart failure or under metabolic inhibitions. 28 The unresolved issue is whether such inhomogeneous [Ca 2þ ] i dynamics reflect pro-arrhythmogenic conditions for atrial fibrillation.…”

“…For these reasons, integrated experimental approaches are required for understanding the direct relevance of the molecular, functional, and morphological abnormalities to genesis of arrhythmias. In this review article, we will overview mechanisms of cardiac arrhythmogenesis that were revealed mainly by functional imaging studies of the living myocardium . We will focus on the roles of intracellular Ca + dynamics, gap junctions, myofibroblasts, and cell‐structural and histoanatomic features of the myocardium in the genesis of cardiac arrhythmias.…”

“…In this review article, we will overview mechanisms of cardiac arrhythmogenesis that were revealed mainly by functional imaging studies of the living myocardium. [6][7][8][9][10][11][12] We will focus on the roles of intracellular Ca 2þ dynamics, gap junctions, myofibroblasts, and cell-structural and histoanatomic features of the myocardium in the genesis of cardiac arrhythmias. The updated, general principles of electro-centric arrhythmogenesis can be assessed by reference to another review article.…”