Excitation-dependent intracellular Ca2+ waves at the border zone of the cryo-injured rat heart revealed by real-time confocal microscopy

H. TANAKA, M. OYAMADA, E. TSUJII, T. NAKAJO AND T. TAKAMATSU. Excitation-Dependent Intracellular Ca2+ Waves at the Border Zone of the Cryo-injured Rat Heart Revealed by Real-time Confocal Microscopy. Journal of Molecular and Cellular Cardiology (2002) 34, 1501-1512. Intracellular Ca2+ waves, which develop under Ca2+-overloaded conditions of the injured myocardium, are regarded as an important substrate for triggered arrhythmias. However, little is known about whether Ca2+ waves arise or become proarrhythmic in the injured heart in situ. On the hypothesis that injured myocardium manifests frequent Ca2+ waves and produce an oscillatory [Ca2+](i) rise leading to triggered activity, we applied cryo-injury to the epicardial surface of fluo 3-AM-loaded perfused rat hearts and analyzed spatiotemporal [Ca2+](i) changes at border zones of the injured myocardium using real-time confocal microscopy. In intact regions Ca2+ waves barely emerged, whereas the border zone myocardium exhibited frequent Ca2+ waves, propagating randomly within the individual cells. Two different types of Ca2+ waves were identified: highly frequent waves (159.6 +/- 86.5 waves/min/cell, n = 266) adjacent to the cryo-ablated regions, and less frequent waves (79.0 +/- 50.1 waves/min/cell, n = 160) slightly farther (>2 cells) away from the ablated regions (vicinities). The former Ca2+ waves emerged asynchronously to Ca2+ transients. Contrariwise, the latter depended on ventricular excitation: they vanished instantaneously on Ca2+ transients, but emerged more frequently and propagated more swiftly after cessation of higher-frequency pacing. Immediately after 3-Hz pacing, some cryo-injured hearts exhibited oscillatory [Ca2+](i) rises; an instantaneous and synchronous elevation of [Ca2+](i) followed by burst occurrence of Ca2+ waves with a gradual decrease in incidence and propagation velocity in a considerable number of cells. These observations indicate that myocardial injury induces Ca2+ waves in the heart, and that their synchronous occurrence could become a substrate for triggered arrhythmias. (C) 2002 Published by Elsevier Science Ltd.