Abstract
Pulmonary vein (PV) cardiomyocytes have the potential to generate spontaneous activity, in contrast to working myocytes of atria. Different electrophysiological properties underlie the potential automaticity of PV cardiomyocytes, one being the hyperpolarization-activated inward current (Ih), which facilitates the slow diastolic depolarization. In the present study, we examined pharmacological characteristics of the Ih of PV cardiomyocytes in rat, guinea pig and rabbit. The results showed that guinea pig and rat PV cardiomyocytes possessed sizeable amplitudes of the Ih, and the Ih of guinea pig was suppressed by Cs+, a blocker of the hyperpolarization-activated cation current. However, the Ih of rat was not suppressed by Cs+, but by Cd2+, a blocker of the Cl− current. The current density of the Ih of rabbit PV cardiomyocytes was significantly smaller than those of other species. This suggests that the ion channels that carry the Ih of PV cardiomyocytes differ among the animal species.
Highlights
The striated myocardium extends from the left atrium (LA) into the ostia of the pulmonary veins (PV), and ectopic activity in the PV myocardium often accounts for initiation and maintenance of atrial fibrillation (AF), the most frequent sustained arrhythmia encountered in clinical practice [1]
Hyperpolarization-activated current (Ih) is due to Hyperpolarization-activated cation current (If) in guinea pig, and ICl,h is the major component of the Ih in rat PV cardiomyocytes
Okamoto et al showed that Cl− channel blockers attenuated the noradrenaline-induced automaticity in rat PV cardiomyocytes [11]. These findings indicate that the inward current systems, which are activated at the pacemaker range, are more or less able to contribute to spontaneous depolarization under the reduced Inwardly rectifying K + current (IK1) density of PV cardiomyocytes
Summary
The striated myocardium extends from the left atrium (LA) into the ostia of the pulmonary veins (PV), and ectopic activity in the PV myocardium often accounts for initiation and maintenance of atrial fibrillation (AF), the most frequent sustained arrhythmia encountered in clinical practice [1]. Electrophysiological experiments demonstrated various types of spontaneous activity in PV cardiomyocytes in animal studies [4] These include sinoatrial node-like spontaneous action potentials [5, 6], digitalis-induced arrhythmia [7, 8], noradrenalineinduced automaticity [9,10,11], stretch-induced automaticity [12] and pacing-induced spontaneous activity [6, 13, 14]. The reversal potential was near − 20 mV at the 40-mM [Cl−]i and 148.9-mM [Cl−]o conditions, and was shifted to depolarized potentials by increasing [Cl−]i or by decreasing [Cl−]o These characteristics are totally different from those of an If or a K+ current (IKH) [18], which was attributed to the Ih in dog PV cardiomyocytes. We examined the species differences of the Ih of PV cardiomyocytes isolated from rat, guinea pig and rabbit under identical experimental conditions
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