0456 : Comparison of spontaneous calcium release events in pulmonary vein and left atria cardiomyocytes

Abstract

Pulmonary veins (PV) have been involved in the onset of atrial fibrillation in humans. In rat, we reported a catecholaminergic automatic activity in PV cardiomyocytes (CM) and not in the left atria (LA). Our objective was to identify differences in calcium cycle between PV and LA CM which could explain the arrhythmogenic potential of PV since cytoplasmic calcium oscillations precede variations of membrane potential which are involved in arrhythmias. Confocal fluorescence imaging was performed in rat isolated CM with di- 8-ANEPPS to study tranverse tubule organization, with specific antibodies for ryanodine receptors and L-type calcium channels (RyR-Cav1.2) coupling, with fluo-4 for spontaneous calcium events (SCaE) frequency determination and calcium transient amplitude. Calcium current was recorded with a wholecell patch clamp technique. Spontaneous calcium events frequency was significantly (p<0.001) higher in PV than in LA CM (15,7 ± 0,7 SCaE/100μm/sec, n= 132 vs 10,9 ± 0,7 SCaE/100μm/sec, n= 120). This can be associated with 1) a higher percentage of cells showing a transverse tubule organization in PV than in LA CM (61,6%, n=86 vs 21,2%, n=85; P<0.001) and among these cells, 2) a better tranverse tubule organization in PV than LA CM (power = 47,6 ± 0,7, n= 86 vs 43,2 ± 0,9, n= 26; P<0.01) and 3) a better RyR-Cav1.2 coupling in PV compared to LA. Moreover, in patch-clamp experiments, we showed a significantly (p<0.001) higher density of calcium current in PV than in LA CM (4.81 ± 0,29pA/pF, n=30 vs 3.00 ± 0,28pA/pF, n=20). A 63% increase of the calcium transient amplitude was observed in PV compared to LA CM and this was associated with a more important sarcomere shortening (x 4.8, n=7 for LA and 31 for PV). In conclusion, the tranverse tubule organization associated with more important calcium exchanges support the higher spontaneous calcium events frequency observed in PV CM. This could be related to the arrhythmogenic potential of PV CM.