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Circ Res ; 99(7): e65-73, 2006 Sep 29.
Article in English | MEDLINE | ID: mdl-16960102

ABSTRACT

Optical mapping studies have suggested that intracellular Ca2+ and T-wave alternans are linked through underlying alternations in Ca2+ cycling-inducing oscillations in action potential duration through Ca2+-sensitive conductances. However, these studies cannot measure single-cell behavior; therefore, the Ca2+ cycling heterogeneities within microscopic ventricular regions are unknown. The goal of this study was to measure cellular activity in intact myocardium during rapid pacing and arrhythmias. We used single-photon laser-scanning confocal microscopy to measure Ca2+ signaling in individual myocytes of intact rat myocardium during rapid pacing and during pacing-induced ventricular arrhythmias. At low rates, all myocytes demonstrate Ca2+ alternans that is synchronized but whose magnitude varies depending on recovery kinetics of Ca2+ cycling for each individual myocyte. As rate increases, some cells reverse alternans phase, giving a dyssynchronous activation pattern, even in adjoining myocytes. Increased pacing rate also induces subcellular alternans where Ca2+ alternates out of phase with different regions within the same cell. These forms of heterogeneous Ca2+ signaling also occurred during pacing-induced ventricular tachycardia. Our results demonstrate highly nonuniform Ca2+ signaling among and within individual myocytes in intact heart during rapid pacing and arrhythmias. Thus, certain pathophysiological conditions that alter Ca2+ cycling kinetics, such as heart failure, might promote ventricular arrhythmias by exaggerating these cellular heterogeneities in Ca2+ signaling.


Subject(s)
Arrhythmias, Cardiac/physiopathology , Calcium Signaling , Cardiac Pacing, Artificial , Heart/physiopathology , Intracellular Membranes/metabolism , Tachycardia, Ventricular/physiopathology , Animals , Calcium/metabolism , In Vitro Techniques , Kinetics , Microscopy, Confocal , Myocardium/metabolism , Myocytes, Cardiac , Pericardium/physiopathology , Rats , Tachycardia, Ventricular/etiology , Temperature
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