胺碘酮对模拟缺氧状态下大鼠心室肌细胞瞬时外向和内向整流钾电流的影响

目的通过观察胺碘酮对模拟缺氧状态下急性分离的大鼠心室肌单细胞复极相中瞬时外向钾电流(Ito)和内向整流钾电流(IK1)通道的影响,探讨其在该条件下抗心律失常的作用机制。方法使用酶解法分离获取大鼠单个心室肌细胞,通过持续通以模拟缺氧细胞外液建立体外模拟缺氧模型,采用全细胞膜片钳实验技术研究胺碘酮对该条件下Ito和IK1的作用。结果胺碘酮呈剂量依赖性降低Ito和IK1电流幅值,对Ito抑制效应的起始浓度为1μmol/L,100μmol/L时抑制作用达最大,最大抑制幅度为56.78%±4.27%(23.98±2.18pA/pFvs10.38±4.27pA/pF;测试电压为+70mV;P<0.01;n=5),IC50(半数抑制浓度)为74.35μmol/L,但Ito的I-V曲线趋势并没有发生变化,稳态激活和失活曲线几乎不发生移动。胺碘酮对IK1内向电流部分抑制起始浓度为1μmol/L,外向电流部分抑制效应的起始浓度为2μmol/L,其最大抑制幅度分别为58.77%±10.76%(56.32±7.24pA/pFvs23.22±7.30pA/pF;测试电压为-150mV;P<0.01)和33.29%±2.15%(6.70±0.89pA/pFvs4.46±0.93pA/pF;测试电压为+40mV;P<0.01;n=5)。对内向电流成分的IC50为63.75μmol/L,IK1通道的稳态激活曲线无明显改变。结论在大鼠离体心室肌单细胞模拟缺氧条件下,胺碘酮对Ito和IK1电流幅度呈剂量依赖性抑制,有对抗缺氧本身造成的动作电位时程缩短效应;对I内向电流成分的敏感性高于外向成分。

Effect of Amiodarone on Ito and IK1 in rat ventricular myocytes under simulated hypoxic condition

Objective To study the acute effect of Amiodarone on the activity of Ito and IK1 of freshly isolated rat ventricular myocytes under simulated hypoxia condition and investigated the antiarrhythmic molecular mechanism of Amiodarone. Methods Collagenase and protease were used to procure single ventricular myocytes, we established the simulated hypoxia model and investigated whether Amiodarone affected the two important potassium ion currents by whole-cell patch-clamp technique. Results The suppressive effect of Amiodarone on the cardiac Ito current density was dose-dependent in the range of 1-100 μmol/l with the IC50 value of 74.35 μmol/l, the maximal suppression was up to 56.78%±4.27%(23.98±2.18 pA/pF vs 10.38±4.27 pA/pF; at 70 mV; P<0.01; n=5) by 100 μmol/l Amiodarone, but the tendency of the I-V curve, the steady state activation and inactivation curve were not changed. The suppressive effect of Amiodarone on the IK1 current density was dose-dependent. Amiodarone significantly reduced IK1 in both inward (56.32±7.24 pA/pF vs 23.22±7.30 pA/pF; 58.77%±10.76% at -150 mV; P< 0.01) and outward directions (6.70±0.89 pA/pF vs 4.46±0.93 pA/pF; 33.29%±2.15% at +40 mV; P< 0.01; n= 5), the IC50 of the inward direction was 63.75 μmol/l. The steady-state activation curve of IK1 had not been altered. Conclusions Amiodarone inhibits both the Ito and IK1 currents in a positive dose-dependent manner in the range of 1-100 μmol/l, and the sensitivity on the inward and outward directions of the IK1 is different. It demonstrates that Amiodarone can antagonize the shorting of the APD by hypoxia itself and has antiarrhythmic effect on the ventricle under the simulated hypoxia condition.