Comparative study of hyperpolarization-activated currents in pulmonary vein cardiomyocytes isolated from rat, guinea pig, and rabbit.

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 (I), which facilitates the slow diastolic depolarization. In the present study, we examined pharmacological characteristics of the I of PV cardiomyocytes in rat, guinea pig and rabbit. The results showed that guinea pig and rat PV cardiomyocytes possessed sizeable amplitudes of the I, and the I of guinea pig was suppressed by Cs, a blocker of the hyperpolarization-activated cation current. However, the I of rat was not suppressed by Cs, but by Cd, a blocker of the Cl current. The current density of the I of rabbit PV cardiomyocytes was significantly smaller than those of other species. This suggests that the ion channels that carry the I of PV cardiomyocytes differ among the animal species.