T-type calcium current in electrical activity of cardiomyocytes isolated from rabbit pulmonary vein

T-Type Calcium Current in PV Cardiomyocytes. Introduction: Pulmonary veins (PVs) are known to initiate paroxysmal atrial fibrillation. T-type calcium current (ICa-T) has a role in normal and abnormal automaticity of cardiomyocytes. The aim of this study was to evaluate whether ICa-T contributes to PV electrical activity. Methods and Results: By whole-cell clamp techniques in rabbit myocytes, ICa-T was identified in 12 (39%) of 31 PV cardiomyocytes with pacemaker activity, 2 (9%) of 23 PV cardiomyocytes without pacemaker activity, and 2 (15%) of 13 atrial myocytes (P<0.05). Maximum ICa-L and ICa-T densities from PV cardiomyocytes with pacemaker activity were 6.87+/-2.17 pA/pF and 1.38+/-0.69 pA/pF, respectively. Nickel (40 muM) decreased the spontaneous activity in 5 (36%) of 14 PV cardiomyocytes (3.1+/-0.6 Hz vs 2.2+/-0.5 Hz, P<0.05), reduced the amplitudes of delayed afterdepolarization from 13+/-1 mV to 7+/-1 mV (n=4, P<0.05) and inhibited transient inward currents from 1.2+/-0.2 pA/pF to 0.7+/-0.1 pA/pF (n=11, P<0.01). Conclusions: We conclude that ICa-T contributes to PV pacemaker activity and triggered activity, which are of functional importance in PV arrhythmogenesis.