Noble D
J Physiol (Paris). 1980;76(2):89-95.
The processes of excitation-contraction coupling in skeletal and cardiac muscles show some very important differences. In skeletal muscle, the action potential is primarily a trigger mechanism for mechanical events which are much slower, whereas in cardiac muscle the electrical activity continues to control the mechanical response even after the initial triggering has occurred. To some extent the control is dependent on a calcium-sodium current which is activated during the action potential plateau. However, this is not the only process by which the force of cardiac contraction may be controlled, since there is evidence that changes in intracellular calcium may also be produced as a secondary consequence of the activity of the sodium-potassium exchange pump. Experiments with cardiac glycosides cast doubt on whether this effect is necessarily linked with a sodium gradient change. In particular, therapeutic levels of the glycosides may increase rather than decrease the Na+ and K+ gradients. The mechanism of the therapeutic action of the cardiac glycosides is therefore still unknown.
骨骼肌和心肌中兴奋-收缩偶联过程存在一些非常重要的差异。在骨骼肌中，动作电位主要是引发机械活动的触发机制，而机械活动要慢得多，而在心肌中，即使在最初的触发发生后，电活动仍继续控制机械反应。在某种程度上，这种控制依赖于动作电位平台期激活的钙-钠电流。然而，这并不是控制心肌收缩力的唯一过程，因为有证据表明细胞内钙的变化也可能是钠钾交换泵活动的次要结果。关于这种效应是否必然与钠梯度变化相关，强心苷实验对此提出了质疑。特别是，强心苷的治疗水平可能会增加而不是降低Na+和K+梯度。因此，强心苷治疗作用的机制仍然未知。
