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Comparison of Ca²⁺-handling properties of canine pulmonary vein and left atrial cardiomyocytes

Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal, Montreal, Quebec, Canada

Submitted 8 July 2005 ; accepted in final form 7 June 2006

Cardiac tissue in the pulmonary vein sleeves plays an important role in clinical atrial fibrillation. Mechanisms leading to pulmonary vein activity in atrial fibrillation remain unclear. Indirect experimental evidence points to pulmonary vein Ca²⁺ handling as a potential culprit, but there are no direct studies of pulmonary vein cardiomyocyte Ca²⁺ handling in the literature. We used the Ca²⁺-sensitive dye indo-1 AM to study Ca²⁺ handling in isolated canine pulmonary vein and left atrial myocytes. Results were obtained at 35°C and room temperature in cells from control dogs and in cardiomyocytes from dogs subjected to 7-day rapid atrial pacing. We found that basic Ca²⁺-transient properties (amplitude: 186 ± 28 vs. 216 ± 25 nM; stimulus to half-decay time: 192 ± 9 vs. 192 ± 9 ms; atria vs. pulmonary vein, respectively, at 1 Hz), beat-to-beat regularity, propensity to alternans, -adrenergic response (amplitude increase at 0.4 Hz: 96 ± 52 vs. 129 ± 61%), number of spontaneous Ca²⁺-transient events after Ca²⁺ loading (in normal Tyrode: 0.9 ± 0.2 vs. 1.3 ± 0.2; with 1 µM isoproterenol: 7.6 ± 0.3 vs. 5.1 ± 1.8 events/min), and caffeine-induced Ca²⁺-transient amplitudes were not significantly different between atrial and pulmonary vein cardiomyocytes. In an arrhythmia-promoting model (dogs subjected to 7-day atrial tachypacing), Ca²⁺-transient amplitude and kinetics were the same in cells from both pulmonary veins and atrium. In conclusion, the similar Ca²⁺-handling properties of canine pulmonary vein and left atrial cardiomyocytes that we observed do not support the hypothesis that intrinsic Ca²⁺-handling differences account for the role of pulmonary veins in atrial fibrillation.

arrhythmia; heart rhythm disorders; ion transport; supraventricular arrhythmia

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