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

Introduction: Pulmonary veins (PVs) are known to initiate paroxysmal atrial fibrillation. T-type calcium current (I_Ca-T) has a role in normal and abnormal automaticity of cardiomyocytes. The aim of this study was to evaluate whether I_Ca-T contributes to PV electrical activity. Methods and Results: By whole-cell clamp techniques in rabbit myocytes, I _Ca-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 I_Ca-L and I_Ca-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 μM) 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 I_Ca-T contributes to PV pacemaker activity and triggered activity, which are of functional importance in PV arrhythmogenesis.