We used the patch-clamp technique to study the effects of amphetamine on th
e membrane currents responsible for rat cardiac action-potential duration.
Amphetamine has no effect on the slow inward Ca2+ current (I-Ca-L), the inw
ardly 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 o
utward K+ current is largely responsible for action-potential repolarizatio
n and fur the regional differences in action-potential duration in rat vent
ricle. Therefore, the reduction of the transient outward K+ current (I-to)
caused by amphetamine may facilitate the appearance of ventricular tachycar
dia and fibrillation, a reported cause of death in amphetamine users.