Effect of Changes in Cycle Length on Diastolic Depolarization Produced by Ouabain in Canine Purkinje Fibers
Effect of Changes in Cycle Length on Diastolic Depolarization Produced by Ouabain in Canine Purkinje Fibers
复制标题
周期长度的变化对犬浦肯野纤维中哇巴因产生的舒张期去极化的影响
作者：
Larry D. Davis
用哇巴因（2.1 × 10− 7 M）处理以630 msec周期刺激的离体犬乳头肌-假腱组织制备物，直至浦肯野纤维舒张期去极化斜率增加。然后测试了周期长度变化对斜率的影响。周期长度的持续缩短增加了斜率，而持续延长则有相反的效果。在驱动搏动的第3相期间由刺激引起的周期长度的突然减少诱导了一个或多个后续周期的舒张期去极化斜率的增加。该过程偶尔导致自发产生的动作电位传播到周围组织。刺激暂停后常出现自发性搏动。缩短周期长度缩短了发作时间，增加了自发性搏动的数量和频率。这些效应与舒张期去极化斜率的增加相关。哇巴因使假腱中浦肯野纤维的舒张期去极化比肌肉表面浦肯野纤维的去极化更早且程度更大。这些研究结果表明，增强浦肯野纤维的舒张期去极化的自发放电的动作电位点可能是一种常见的手段，洋地黄产生各种室性心律失常在完整的动物观察。
Isolated canine papillary muscle–false tendon tissue preparations stimulated at a cycle length of 630 msec were treated with ouabain (2.1 × 10−7M) until an increase in the slope of diastolic depolarization of Purkinje fibers was produced. Then the effects of changes in cycle length on the slope were tested. Sustained shortening of the cycle length increased the slope, and sustained lengthening had the opposite effect. An abrupt decrease in cycle length caused by a stimulus during phase 3 of a driven beat induced an increase in the slope of diastolic depolarization for one or more subsequent cycles. This procedure occasionally led to the spontaneous generation of an action potential which propagated into surrounding tissue. Suspension of stimulation often was followed by spontaneous beats. Shortening of the cycle length decreased the time of onset and increased the number and frequency of spontaneous beats. These effects were correlated with increases in the slope of diastolic depolarization. The diastolic depolarization of Purkinje fibers in false tendons was increased earlier and to a greater degree by ouabain than was the depolarization of Purkinje fibers on the muscle surface. These findings suggest that enhancement of diastolic depolarization of Purkinje fibers to the point of spontaneous discharge of action potentials may be a common means by which digitalis produces a variety of ventricular arrhythmias observed in intact animals.