Species Difference in the Contribution of T-Type Calcium Current to Cardiac Pacemaking as Revealed by R(−)-Efonidipine

抄録

The contribution of the T-type Ca²⁺ current to cardiac pacemaking was examined in isolated right atrial tissue from the mouse, guinea pig, and rabbit using a specific blocker, R(−)-efonidipine. At 10⁻⁶ M, R(−)-efonidipine produced negative chronotropy, which was prominent in the mouse and small but significant in the guinea pig. No effect was observed in the rabbit. Microelectrode recordings revealed that R(−)-efonidipine significantly prolongs the pacemaker (phase 4) depolarization of the sinoatrial-node action potential in the mouse and guinea pig. These results provide the first pharmacological evidence that the contribution of T-type Ca²⁺ current to cardiac pacemaking differs among experimental animal species.