Effects of amphetamine on calcium and potassium currents in rat heart.

We used the patch-clamp technique to study the effects of amphetamine on the membrane currents responsible for rat cardiac action-potential duration. Amphetamine has no effect on the slow inward Ca2+ current (I(Ca)-L), the inwardly rectifying K+ current (I(K1) and the outward K+ delayed rectifier (I(K)) and sustained (I(SS)) currents. Amphetamine blocks the transient outward K+ current (I(to)) both in the open and in the rested state. The transient outward K+ current is largely responsible for action-potential repolarization and for the regional differences in action-potential duration in rat ventricle. Therefore, the reduction of the transient outward K+ current (I(to)) caused by amphetamine may facilitate the appearance of ventricular tachycardia and fibrillation, a reported cause of death in amphetamine users.