Surawicz B
Department of Medicine, Indiana University School of Medicine, Indianapolis 46202-4800.
Cardiovasc Res. 1992 Nov;26(11):1021-9. doi: 10.1093/cvr/26.11.1021.
This review examines the putative role played by three repolarising potassium currents, namely the transient outward current (ito), the inward rectifying current (iK1), and the late outward rectifying current (iK), in the regulation of action potential duration in cardiac Purkinje and ventricular muscle fibres under normal physiological conditions. The role of other potassium currents, including the ATP activated current (iK,ATP) under these conditions is uncertain. Personal experiences and work of others are reviewed to summarise: (1) regulation of normal cycle length dependent action potential duration: (2) the characteristics of ito, iK1, and iK pertinent to repolarisation; and (3) the effects of potassium channel blockers and activators on cycle length dependent action potential duration. The presence of ito creates a notch after depolarisation and limits action potential duration at long cycles. Block of iK1 prolongs action potential duration predominantly by slowing phase 3 of the action potential. Block of iK prolongs the duration predominantly by lengthening phase 2 of the action potential, and the lengthening becomes more pronounced at longer cycles. Activation of iK,ATP shortens the duration, and the shortening becomes more pronounced at longer cycles. Each of the three major repolarising potassium currents appears to play a different role in modulating the action potential duration. Ito creates a notch which resets the early course of plateau, and also limits the duration at long cycles. IK1 contributes to maintenance of plateau and controls repolarisation course during phase 3 of the action potential. IK plays major role in controlling action potential duration within a wide range of cycle lengths in Purkinje fibres, and when present, also in ventricular muscle fibres.
本综述探讨了三种复极化钾电流，即瞬时外向电流（ito）、内向整流电流（iK1）和晚期外向整流电流（iK），在正常生理条件下对心脏浦肯野纤维和心室肌纤维动作电位时程调节中所起的假定作用。在这些条件下，其他钾电流的作用，包括ATP激活电流（iK,ATP）尚不确定。通过回顾个人经验及他人的研究工作进行总结：（1）正常周期长度依赖性动作电位时程的调节；（2）与复极化相关的ito、iK1和iK的特性；（3）钾通道阻滞剂和激活剂对周期长度依赖性动作电位时程的影响。ito的存在在去极化后产生一个切迹，并在长周期时限制动作电位时程。阻断iK1主要通过减慢动作电位的3期来延长动作电位时程。阻断iK主要通过延长动作电位的2期来延长时程，且在长周期时延长更明显。激活iK,ATP可缩短时程，且在长周期时缩短更明显。三种主要的复极化钾电流似乎在调节动作电位时程中发挥不同作用。Ito产生一个切迹，重置平台期的早期进程，并在长周期时限制时程。IK1有助于维持平台期，并控制动作电位3期的复极化进程。IK在控制浦肯野纤维以及存在时在心室肌纤维的广泛周期长度范围内的动作电位时程中起主要作用。
