家兔心室肌细胞的非特异性阳离子流

目的已知有多种离子流参与动作电位的复极过程,而每种复极电流的特性及大小因动物的种属不同而不同,电流对复极所起作用的大小也不同。家兔心室肌细胞的Ito属于慢失活的电流,它几乎贯穿于整个复极相,这导致兔心室肌的复极过程非常复杂。本研究以家兔为研究对象,探索兔心室肌上是否存在其他复极电流,并研究它的特性,推测其在致、抗心律失常中的作用。方法应用全细胞膜片钳制技术记录兔心室肌单细胞电流。结果研究发现兔的心室肌细胞存在非特异性阳离子流：当电极内外液中的K^＋用Cs^＋替代后,去极化电位引发一组非时间依赖性电流,这种电流可以被Gd^3＋（非特异性阳离子流的有效阻断剂）阻断。当从灌流液中去掉Ca^2＋、Mg^2＋后,这种电流的幅值在＋60mV时增加40％～116％;当在灌流液中加入20μmol／L的胰岛素后,这种电流的幅值在＋60mV时增加30％～60％。结论兔的心室肌细胞存在非特异性阳离子流,鉴于它快激活、无失活并呈电压依赖性,我们推测这种电流对动作电位的各个时相包括兔心室肌的静息膜电位都有重要的影响,特别是动作电位的复极阶段。可以设想,在某些病理生理条件下,该通道的通透性可能会发生改变,这将导致心律失常的发生,或者抗心律失常。

An nonselective cation current in rabbit ventricle myocytes

OBJECTIVE: Currents contributing repolarization in rabbit ventricular myocyte are very complex since the I(To.s) covers almost the whole repolarization phase of the action potential. The other components of repolarizing currents, as I(Kr) and I(Ks) are small. The purpose of this study is to investigate whether or not there are other currents in rabbit ventricular repolarization. METHODS: Ion currents of rabbit ventricular myocyte were recorded using the whole-cell patch-clamp technique. RESULTS: In the present work, an nonselective cation current was identified by replacing the K(+) with Cs(+) in the bathing and pipette solutions. The outward current elicited by depolarizing potentials could be inhibited by Gd(3+), an effective inhibitor of nonselective cation currents. Depleting Ca(2+) and Mg(2+) in the bathing solution, the amplitudes of this outward current increased by 40%-116% at +60 mV, and adding 2 micromol/L insulin to the solution (with normal concentration of Ca(2+) and Mg(2+) in Tyrode's solution), the amplitude increased by 30%-60% at +60 mV. CONCLUSION: It is suggested that a nonselective cation current in rabbit ventricular myocytes may play an important role in the repolarization of the action potential in rabbit ventricle. Changes of nonselective cation current will lead to induce or inhibit arrhythmia.