酚噻嗪对豚鼠心室肌细胞动作电位时程和跨膜离子电流作用的研究

Effects of Phenothiazine on Actoin Potential Duration and Main Ion Currents Involved in the Depolarization and Repolarization of Isolated Guinea Pig Ventricular Myocytes

通过观察酚噻嗪对豚鼠单心室肌细胞动作电位时程 (APD)及动作电位形成过程中主要离子通道的作用 ,探讨其诱发长QT间期 (LQT)综合征及室性心律失常的可能机制。采用膜片钳技术中的Nystatin 破膜法观察酚噻嗪对豚鼠心室肌细胞APD的作用 ,采用全细胞技术研究酚噻嗪对心室肌细胞动作电位形成过程中主要离子电流的作用。结果 :①在 5Hz剌激频率时 ,10 0 μmol/L酚噻嗪使APD90 延长 2 5 .8%± 3.8% (n =10 ,P <0 .0 1) ,作用呈部分可逆性 ;②在分别持续 2 5 0ms和 10 0 0ms至不同膜电位水平去极化的实验中 ,酚噻嗪对延迟整流钾电流 (IK)尾电流有明显的抑制作用 ,在 +6 0mV持续 2 5 0ms的去极化时 ,5 0 .6 4 %± 6 .4 6 %的IK尾电流受抑制 (n =7,P <0 .0 5 ) ,这一抑制作用呈浓度依赖性 ,半抑制浓度 (IC50 ) =2 5 .98μmol/L ,Hill常数为 0 .75。当采用IK快速激活成分 (IKr)的特异性阻断剂E 4 0 31阻断IKr后 ,酚噻嗪对IK尾电流的阻断作用消失。 30 0 μmol/L酚噻嗪对IKr的抑制作用仍弱于 0 .5mmol/LE 4 0 31。在 10 0 0ms,至 +2 0mV去极化的情况下 ,酚噻嗪对IK尾电流的IC50 为 2 5 .98μmol/L ,这一抑制作用可部分洗脱。受酚噻嗪抑制的电流与IK中IKr具有相似的通道动力学特性 ;③未发现酚噻嗪对IK稳态电流、IK?

There have been reports of long QT (LQT),even unexpected sudden cardiac death after the administration of phenothiazine, but the mechanisms were not well understood.In this experiment,effects of phenothiazine on action potential duration (APD) of single guinea pig ventricular myocytes were studied by using Nystatin-perfortated configuration and the conventional whole-cell configuration of the patch-clamp techniques.Results:At a stimulation frequency of 5 Hz,phenothiazine (100 μmol/L) prolonged APD 90by 25.8%±3.8%(n=10,P<0.01),and the effect was reversible.Phenothiazine decreased the tail currents of delayed rectifier potassium current(I K) elicited by both short (250 msec) and long (1000 msec) depolarization protocols at any membrane potential from -10 mV to +60 mV.Phenothiazine 100 μmol/L decreased about 50.64%±6.46% (n=7, P<0.05) I K tail current when the myocytes were depolarized to +60 mV for 250msec, and the effects were dose-dependent and partly reversible,with an IC 50 of 25.98 μmol/L and a Hill coefficient of 0.75.When the rapidly activating component of I K(I Kr) was first blocked by E-4031,phenothiazine had no effect on the slowly activating component of I K(I Ks).The current inhibited by phenothiazine had the same characteristics of the I Krof I K. We failed to find any effect of the drug on I Ksteady state current,the inward rectifier potassium current (I K1), sodium current (I Na) and calcium current (I Ca).Conclusion:Phenothiazine selectively blocked I Krof I K. The results can partly explain LQT and ventricular arrhythmias after administration of the drug.