Ca
2+
overload is a cardinal feature of cardiomyocyte injury, and its progression to irreversible state leads to cell death. However, unknowns are the precise spatiotemporal changes in the myocyte Ca
2+
dynamics and the relevant cell morphology of irreversibly injured hearts. On the hypothesis that myocytes exhibit high-frequency Ca
2+
waves and contraction band necrosis in saponin-permeabilized injured heart, we observed changes in the Ca
2+
dynamics and the relevant morphological changes in the subepicardial myocardium of the Fluo4-loaded rat hearts (n = 14) by rapid-scanning confocal microscopy (100 frames/s) under Langendorff perfusion with 0.3 mM Ca
2+
-Tyrode solution including 0.4 % saponin at 30°C. Also performed was confocal imaging of tetramethylrhodamine methyl ester (TMRM) fluorescence of the myocardium. Under quasi-quiescence of the heart after dissection of the SA node, individual myocytes barely exhibited spontaneous Ca
2+
waves, whereas after commencement of saponin perfusion high-frequency (118 ± 9.7 /min/cell, mean ± SEM) Ca
2+
waves (hereafter, “agonal waves”) emerged within 1 min, showing asynchronous, oscillatory contractions in the individual myocytes with a V
prop
of 124 ± 2.5 μm/s (n = 60). Subsequently, the waves gradually decreased in frequency with concomitant slowing of its decay time course, and eventually, disappeared in 6 min; myocytes exhibited high, static Fluo4-fluorescence intensity. Along with the progression of Ca
2+
overload by saponin, the TMRM fluorescence intensity was discretely lost in individual myocytes. The myocytes showing the agonal waves exhibited contraction bands, i.e., band-like aggregations of the actin fibers. Under mechanical arrest of the heart by 2,3-butanedione monoxime (20 mM), saponin still induced the agonal waves with a frequency of 253 ± 10.6 /cell/min and V
prop
of 118 ± 2.1 μm/s (n = 60); however, contraction bands were barely seen.In conclusion, irreversible myocyte injury by saponin provoked agonal Ca
2+
waves and oscillatory contractions indicating progressive Ca
2+
overload and the following mitochondrial damage, which may provide deeper insights into understanding the mechanism of contraction band necrosis.
Quantitative analysis of infarct size, contraction band necrosis, and coagulation necrosis in human autopsied hearts with acute myocardial infarction after treatment with selective intracoronary thrombolysis.