Background: Pulmonary veins (PVs) contain cardiomyocytes with a high arrhythmogenicity for inducing atrial fibrillation. The swelling-activated outwardly rectifying Cl - currents (I Cl,swell) are important in the electrical activity of cardiomyocytes. This study was to investigate whether I Cl,swell play a role in the PV electrophysiological characteristics. Materials and methods: A whole-cell patch clamp was used to investigate the action potentials and I Cl,swell in isolated rabbit single PV and atrial cardiomyocytes during immersion in isotonic (290-300 mosm L -1) and hypotonic (220-230 mosm L -1) solutions. The cell length and cell width were measured using confocal microscopy. Results: Hypotonic solution induced larger I Cl,swell in the PV cardiomyocytes with pacemaker activity than those in the PV cardiomyocytes without pacemaker activity or atrial cardiomyocytes. Hypotonic solution shortened the action potential duration and increased the cell width to a greater extent in the PV cardiomyocytes than in the atrial cardiomyocytes. Moreover, hypotonic solution decreased the PV firing with a decrease in the transient inward currents and delayed after depolarizations. Conclusions: These findings suggest that the I Cl,swell plays an important role in the electrical activity of the PV cardiomyocytes.
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