ИСТИНА

The wall of thoracic (caval and pulmonary) veins in a most mammals and human contains cardiomyocites. Thoracic veins (TCV) cardiomyocites forms a functionally active myocardial tissue that electrically connected to the right or left atrium. Ectopic foci and arrhythmogenic conduction in thoracic veins is responsible for atrial fibrillation initiation. TCV myocardium is extensively developed in rodents including mice. Nevertheless, TCV ectopy in such frequently used experimental animals like mice remains poorly investigated. The present study is aimed to the localization of ectopic activity and characterization of conduction in murine thoracic veins myocardium. Multicellular preparations consisting of left atrium and pulmonary veins (LA-PV); preparations of superior caval veins (SVC) were dissected from male mice (20-25 g) and perfused at 37C with Tirode solution. Excitation was mapped in electrically paced or non-paced preparations treated with potential sensitive (dye di-4-ANEPPS, 5 µM) and blebbistatin (1 µM) with use of CCD camera (WuTech Inst.). Conduction pattern and velocity (CV) were assessed with aid of RedShirtImaging software in control conditions or after adrenaline (AD, 1 μM), isoproterenol (1 μM, ISO) or phenylephrine (10 μM, PHE) administration. All paced mice TVC tissue preparations demonstrated atrial-like action potentials, CV and pattern of excitation. Non-paced TCV preparations were quiescent in most (26 of 32) cases under basal conditions, while adrenergic stimulation caused automaticity both in LA-PV and SVC. The excitation was initiated predominantly in pulmonary veins ostium region similarly in case of AD (6 of 6), ISO (6 of 6) or PHE (2 of 5) administration in LA-PV preparations. Ectopically-derived excitation was conducted continuously and with low anisotropy in LA and PV parts of mice preparations. Automatic firing was much less frequently induced by adrenergic receptors agonists (4 of 15) in SVC; it was always initiated in a most proximal site of veins and propagated in atrial-like manner. In conclusion, murine pulmonary veins myocardium is more prone to adrenergic automaticity then caval vein. Adrenaline induced ectopic foci located in pulmonary veins ostium and proximal regions of SCV. Ectopically-derived excitation demonstrates atrial like pattern in murine thoracic veins.