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

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 similar to58% 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 similar to60 and similar to50%, respectively), whereas transient outward K+ current and L-type Ca2+ current were significantly smaller (by similar to25 and similar to30%, 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.