Résumé
Atrial fibrillation (AF) is the most common sustained form of arrhythmia in human. Numerous studies have showed that Ca2+ signaling is altered during AF, although it has not been established whether Ca2+ remodeling is homogenous across the different regions of the atria. Given the importance of the pulmonary veins (PV) in the treatment of AF (NEJM, 1998, 339:659-66), we have studied the characteristics of Ca2+ transients in 4 different regions of the left atrium (LA) in an animal model close to human.
LA myocytes were obtained by enzymatic dissociation of sheep hearts. Animals were euthanized by injection of pentobarbital and the heart was rapidly excised (guidelines approved by ethical committee). The aorta was cannulated and heart was rinsed with cardioplegic solution. The ventricles and right atrium were removed. LA was cannulated by the circumflex artery and mounted into a Langendorff perfusion system after suture of the leaky atrial branches. LA was perfused with a Ca2+-free solution (~10min), then collagenase and protease solution (0,08mM Ca2+) and recirculated for ~25min. Enzymes were washed out with a 0,2mM Ca2+ solution. LA was separated into 4 regions: Endocardium, Epicardium, roof and PV. Cells were re-suspended into a 1,8mm Ca2+ solution by steps. Ca2+ transients were recorded (Fura-2, field stimulation) using an IonOptix system and cell membrane was stained with di-8 ANNEPS and visualized under confocal microscopy.
Ca2+ tolerant myocytes were obtained from the 4 LA regions. Ca2+ amplitude was similar across all regions, however the time to peak and the time to decay showed significant differences: Epicardium vs roof and PV. Confocal microscopy study showed the presence of t-tubules in all regions.
Those results suggest regional differences in Ca2+ transient may play a major role in the development of atrial arrhythmia. This study will be completed by the development of a sheep model in persistent AF.