Sematilide blocks the inward rectifier potassium channel in isolated guinea pig ventricular myocytes

1. In whole-cell patch recording, the relative potency of the blocking action of sematilide on IK1 was found to be constant at each potential level of IK1 activation. Under more acidic condition, the degree of block was decreased. These results strongly suggested that the neutral form of sematilide may penetrate the cardiac cell membrane via hydrophobic pathway. 2. In cell-attached patches, sematilide prolonged the interburst interval and reduced the opening probabilities of the IK1 channel without affecting either the mean open time or the mean closed time within a burst.