Three distinct types of Ca2+ waves in Langendorff-perfused rat heart revealed by real-time confocal microscopy

Although Ca2+ waves in cardiac myocytes are regarded as arrhythmogenic substrates, their properties in the heart in situ are poorly understood. On the hypothesis that Ca2+ waves in the heart behave diversely and some of them influence the cardiac function, we analyzed their incidence, propagation velocity, and intercellular propagation at the subepicardial myocardium of flue 3-loaded rat whole hearts using real-time laser scanning confocal microscopy. We classified Ca2+ waves into 3 types. In intact regions showing homogeneous Ca2+ transients under sinus rhythm (2 mmol/L [Ca2+](o)), Ca2+ waves did not occur. Under quiescence, the waves occurred sporadically (3.8 waves . min(-1) . cell(-1)), with a velocity of 84 mu m/s, a decline half-time (t(1/2)) of 0.16 seconds, and rare intercellular propagation (propagation ratio <0.06) (sporadic wave). In contrast, in presumably Ca2+-overloaded regions showing higher fluorescent intensity (113% versus the intact regions), Ca2+ waves occurred at 28 waves . min(-1) . cell(-1) under quiescence with a higher velocity (116 mu m/s), longer decline time (t(1/2)=0.41 second), and occasional intercellular propagation (propagation ratio=0.23) (Ca2+-overloaded wave). In regions with much higher fluorescent intensity (124% versus the intact region), Ca2+ waves occurred with a high incidence (133 waves . min(-1) . cell(-1)) and little intercellular propagation (agonal wave). We conclude that the spatiotemporal properties of Ca2+ waves in the heart are diverse and modulated by the Ca2+-loading state. The sporadic waves would not affect cardiac function, but prevalent Ca2+-overloaded and agonal waves may induce contractile failure and arrhythmias.