Cellular electrophysiology of canine pulmonary vein cardiomyocytes: action potential and ionic current properties

Abstract

Pulmonary vein (PV) cardiomyocytes play an important role in atrial fibrillation; however, little is known about their specific cellular electrophysiological properties. We applied standard microelectrode recording and whole-cell patch-clamp to evaluate action potentials and ionic currents in canine PVs and left atrium (LA) free wall. Resting membrane potential (RMP) averaged −66 ± 1 mV in PVs and −74 ± 1 mV in LA (P < 0.0001) and action potential amplitude averaged 76 ± 2 mV in PVs vs. 95 ± 2 mV in LA (P < 0.0001). PVs had smaller maximum phase 0 upstroke velocity (V_max: 98 ± 9 vs. 259 ± 16 V s⁻¹, P < 0.0001) and action potential duration (APD): e.g. at 2 Hz, APD to 90 % repolarization in PVs was 84 % of LA (P < 0.05). Na⁺ current density under voltage-clamp conditions was similar in PV and LA, suggesting that smaller V_max in PVs was due to reduced RMP. Inward rectifier current density in the PV cardiomyocytes was ∼58 % that in the LA, potentially accounting for the less negative RMP in PVs. Slow and rapid delayed rectifier currents were greater in the PV (by ∼60 and ∼50 %, respectively), whereas transient outward K⁺ current and L-type Ca²⁺ current were significantly smaller (by ∼25 and ∼30 %, respectively). Na⁺-Ca²⁺-exchange (NCX) current and T-type Ca²⁺ current were not significantly different. In conclusion, PV cardiomyocytes have a discrete distribution of transmembrane ion currents associated with specific action potential properties, with potential implications for understanding PV electrical activity in cardiac arrhythmias.