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

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_h), which facilitates the slow diastolic depolarization. In the present study, we examined pharmacological characteristics of the I_h 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_h, and the I_h of guinea pig was suppressed by Cs⁺, a blocker of the hyperpolarization-activated cation current. However, the I_h of rat was not suppressed by Cs⁺, but by Cd²⁺, a blocker of the Cl^- current. The current density of the I_h of rabbit PV cardiomyocytes was significantly smaller than those of other species. This suggests that the ion channels that carry the I_h of PV cardiomyocytes differ among the animal species.