Contractile Characteristics of Single Cardiomyocytes in the Myocardial Sleeves of the Pulmonary Veins of Guinea Pigs

Myocardial sleeves of the pulmonary veins (PV) extending fromthe left atrium (LA) are the major source of ectopic activity causingatrial arrhythmias. The structural and electrophysiological characteristicsof the PV myocardium differ from those of the LA. The mechanicalactivity of cardiomyocytes (CM) impacts cardiac excitation-contractioncoupling, however, the mechanical function of PV CM has not beenstudied yet. We compared the characteristics of the actin-myosin interactionand sarcomere length (SL) dynamics in mechanically non-loaded singleCM between the PV and LA in the guinea pig heart. We found thatthe functional properties of myosin from the PV and LA are not different,while the phosphorylation levels of sarcomeric proteins in the PVand LA are different. End-diastolic SL, sarcomere shortening amplitude,and velocities of sarcomere shortening and relengthening of PV andLA CM do not differ, while PV CM are longer and thinner than LACM. The amplitude of sarcomere shortening increased with an increasein CM length in the LA but not in the PV. We assume that an absenceof correlation between the morphometric parameters of CM and the amplitudeof sarcomere shortening together with the electrophysiological featuresof the PV myocardium may contribute to the occurrence and developmentof atrial fibrillation.