Varró A, Papp J G
Department of Pharmacology, Albert Szent-Györgyi Medical University, Szeged, Hungary.
Cardioscience. 1992 Sep;3(3):131-44.
In this article we review results obtained during the last decade by the single cell voltage clamp technique on cardiac ventricular myocytes, and we re-evaluate the major ionic currents underlying the cardiac action potential. Since its introduction into cardiac electrophysiology in the late seventies this technique has greatly contributed to our knowledge about the role of the transmembrane ionic currents in the heart. Recent findings gained with this method have confirmed that the inward sodium current is responsible not only for the fast depolarization, but, in part, also for the maintenance of the plateau phase of the action potential. The kinetics of the inward calcium current measured by the single cell voltage clamp technique proved to be much faster than was previously thought. In addition, two types of the inward calcium current with different physiological roles have recently been identified. The L-type calcium current plays an important part in maintaining the plateau phase of the action potential and may cause depolarization at less negative potentials. Although the physiological significance of the T-type calcium current is less clear, it appears to be involved in the pacemaker function of cardiac tissues. Single cell voltage clamp experiments have shown that the inward rectifier potassium current is not independent of time, as described earlier, but it helps to terminate the final phase of repolarization, and presumably controls the resting membrane potential. Recent studies with the single cell voltage clamp method have revealed that the delayed rectifier potassium current has, most probably, more than one component and is extensively modulated by neurotransmitters. Its main role is to initiate and terminate cardiac repolarization. This current is of particular importance in regulating rate-dependent repolarizations. The transient outward current, which rapidly activates and inactivates after depolarization, initiates early fast repolarization and may also take part in rate-dependent repolarization. The ionic carriers of this current are most likely potassium and chloride. The use of the single cell voltage clamp technique has led to the discovery of formerly unrecognized currents, like the ATP-dependent potassium current, the sodium activated potassium current and the chloride currents. The application of the new technique has made it possible to focus more attention on currents which were difficult to study previously, such as Na/K pump and Na/Ca exchanger currents.
在本文中，我们回顾了过去十年间通过单细胞电压钳技术在心室肌细胞上获得的研究结果，并重新评估了构成心脏动作电位的主要离子电流。自70年代末该技术引入心脏电生理领域以来，它极大地增进了我们对跨膜离子电流在心脏中作用的认识。用此方法获得的最新研究结果证实，内向钠电流不仅负责快速去极化，而且在一定程度上还负责动作电位平台期的维持。通过单细胞电压钳技术测得的内向钙电流动力学比之前认为的要快得多。此外，最近还发现了两种具有不同生理作用的内向钙电流。L型钙电流在维持动作电位平台期方面起重要作用，并且在电位不那么负时可能导致去极化。尽管T型钙电流的生理意义尚不太明确，但它似乎参与心脏组织的起搏功能。单细胞电压钳实验表明，内向整流钾电流并不像之前所描述的那样与时间无关，而是有助于终止复极化的最后阶段，并可能控制静息膜电位。最近用单细胞电压钳方法进行的研究表明，延迟整流钾电流很可能有不止一个成分，并且受到神经递质的广泛调节。它的主要作用是启动和终止心脏复极化。该电流在调节速率依赖性复极化方面尤为重要。瞬时外向电流在去极化后迅速激活和失活，启动早期快速复极化，并且也可能参与速率依赖性复极化。该电流的离子载体很可能是钾离子和氯离子。单细胞电压钳技术的应用导致发现了以前未被认识的电流，如ATP依赖性钾电流、钠激活钾电流和氯电流。新技术的应用使人们能够更加关注以前难以研究的电流，如钠钾泵电流和钠钙交换电流。
