MEMBRANE CALCIUM CURRENT IN VENTRICULAR MYOCARDIAL FIBRES
MEMBRANE CALCIUM CURRENT IN VENTRICULAR MYOCARDIAL FIBRES
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DOI：
10.1113/jphysiol.1970.sp009056
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发表时间：
1970-01-01
影响因子：
5.5
通讯作者：
REUTER, H
中科院分区：
文献类型：
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作者：
BEELER, GW;REUTER, H
1.在条件去极化使钠系统失活的情况下，用电压钳方法可在不干扰初始快钠电流的情况下测量犬心脏的慢内向电流。慢内向电流对[Ca]o的变化非常敏感，在将浴液换成无钠溶液后，它立即出现在INA的平衡电位之上，并在此条件下持续很长时间，没有太大变化，而INaA则迅速消失。河豚毒素和[mg]O对该电流成分无影响。这些结果有力地支持了心肌组织的慢内向电流是由钙离子携带的观点。在泰罗德溶液中，钙电流的起始阈值约为−35 mV，并通过增加或降低[Na]o.向更负的电位移动。与复极化相关的钙敏感内向电流尾部被认为代表在前面的去极化过程中激活的钙电导的比例测量。钙电导在负电位区随时间快速下降，在正电位区随时间缓慢下降。在−35至+50 mV.5的电势范围内，该“失活”过程的时间常数在40至700毫秒之间变化。利用瞬时电流-电压关系，估计钙电流在正常泰罗德溶液中的反转电位约为+60 mV。然而，如附录所示，钙平衡电势不能被认为是恒定的。讨论了钙电流对心脏动作电位平台化的重要性。
1. A slow inward current in ventricular preparations of the dog heart can be measured by the voltage clamp method without interference from the initial rapid sodium current if the sodium system is inactivated by conditioning depolarization.2. The slow inward current is very sensitive to variation in [Ca]o. It occurs above the equilibrium potential ofINaimmediately after changing the bathing fluid to a sodium‐free solution and persists under this condition for a long time without much alteration, whileINais rapidly abolished. Tetrodotoxin and [Mg]ohave no effect on this current component. These results strongly support the view that the slow inward current in cardiac tissue is carried by calcium ions.3. The threshold for initiation of the calcium current is around −35 mV in Tyrode solution and is shifted to more negative potentials by either increasing [Ca]oor reducing [Na]o.4. Calcium sensitive inward current tails associated with repolarization are assumed to represent a proportional measure of calcium conductance activated during the preceding depolarization. Calcium conductance declines rapidly with time in the inside negative potential range and slowly at positive potentials. The time constants for this ‘inactivation’ process vary between 40 and 700 msec in the potential range −35 to +50 mV.5. By using instantaneous current—voltage relations the reversal potential of calcium current was estimated to be about +60 mV in normal Tyrode solution. As shown in the Appendix, however, the calcium equilibrium potential cannot be considered to be constant.6. The importance of the calcium current for the plateau of the cardiac action potential is discussed.