Three Distinct Types of Ca ²⁺ Waves in Langendorff-Perfused Rat Heart Revealed by Real-Time Confocal Microscopy

Abstract

Abstract-Although Ca 2ϩ waves in cardiac myocytes are regarded as arrhythmogenic substrates, their properties in the heart in situ are poorly understood. On the hypothesis that Ca 2ϩ 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 fluo 3-loaded rat whole hearts using real-time laser scanning confocal microscopy. We classified Ca 2ϩ waves into 3 types. ), with a velocity of 84 m/s, a decline half-time (t 1/2 ) of 0.16 seconds, and rare intercellular propagation (propagation ratio Ͻ0.06) (sporadic wave). In contrast, in presumably Ca 2ϩ -overloaded regions showing higher fluorescent intensity (113% versus the intact regions), Ca 2ϩ waves occurred at 28 waves ⅐ min Ϫ1 ⅐ cell Ϫ1 under quiescence with a higher velocity (116 m/s), longer decline time (t 1/2 ϭ0.41 second), and occasional intercellular propagation (propagation ratioϭ0.23) (Ca 2ϩ -overloaded wave). In regions with much higher fluorescent intensity (124% versus the intact region), Ca 2ϩ waves occurred with a high incidence (133 waves ⅐ min Ϫ1 ⅐ cell Ϫ1 ) and little intercellular propagation (agonal wave). We conclude that the spatiotemporal properties of Ca 2ϩ waves in the heart are diverse and modulated by the Ca 2ϩ -loading state. The sporadic waves would not affect cardiac function, but prevalent Ca 2ϩ -overloaded and agonal waves may induce contractile failure and arrhythmias.

Mechanisms of sudden cardiac death

“…Although spontaneous Ca 2+ waves occur in buffer-perfused isolated heart preparations under physiological conditions as well as following injury (17,19,20,44), it is not known whether Ca 2+ waves trigger arrhythmias under ischemic conditions. Conceivably, an increase in the electrical resistance between cardiomyocytes in the acutely ischemic myocardium (45) initiates DAD-related extra beats because reduced intercellular coupling would diminish the opposing, i.e., repolarizing, effect of passive outward current generated by neighboring cardiomyocytes.…”

Three-dimensional simulation of calcium waves and contraction in cardiomyocytes using the finite element method

“…Besides their importance in basic physiology, Ca 2ϩ waves also have clinical relevance because a focal increase in [Ca 2ϩ ] i could activate a transient inward current and membrane depolarization, thus constituting a potentially arrhythmogenic event (2,6). Accordingly, several studies have attempted to clarify the characteristics and underlying mechanisms of Ca 2ϩ waves using single-cell (8,15), multicellular (24), and whole heart (17) preparations.…”

Calcium Spots

“…The recent evolution of three-dimensional microscopy, 18 such as confocal microscopy, multiphoton microscopy, and near-field microscopy, enables not only real-time imaging but also in situ imaging in living tissues or organs, such as vascular smooth muscles 19 and the whole heart. 20 It is reasonable to assume that cell-to-cell communi- spots. Use of a confocal imaging system would allow us to discriminate between the endothelial cells and the smooth muscle cells, and, furthermore, the real-time imaging of the [Ca 2ϩ ] i dynamics in these cell layers along the z-axis would be possible if scanning were conducted using a piezoelectric actuator added to the real-time scanning system.…”