伊伐布雷定对大鼠心脏正性肌力的作用机制

Positive inotropic effect of Ivabradine in rats and its underlying mechanism

目的伊伐布雷定通过抑制I f电流而降低心率,临床用于治疗稳定性心绞痛及心肌缺血;然而其正性肌力作用尚不清楚。文章研究其体内及体外正性肌力作用及其机制。方法采用Millar双压力导管插入正常全麻大鼠右颈动脉,稳定后记录压力-容积环作为空白A组(n=7),经左侧颈外静脉缓慢推注伊伐布雷定(1 mg/kg)药效稳定后记录压力-容积环作为给药A组(n=7),比较空白A组、给药A组的大鼠心输出量、左心室压及动脉压。采用Langendorff法记录离体大鼠左心室压。正常灌流液作为空白B组(n=6),含伊伐布雷定(1,10μmol/L)灌流液为给药B组(n=6);此外,3种抑制剂(PKA抑制剂H89,CaMKⅡ抑制剂KN-93,PP1、PP2A抑制剂(Calyculin A)对伊伐布雷定效应干预作用实验方案为:将正常灌流液设置为H89、KN-93及CA对照组,将H89(200 nmol/L)、KN-93(500 nmol/L)、CA(10 nmol/L)分别设置为H89、KN-93、KN-93处理组,另将伊伐布雷定(10μmol/L)+H89(200 nmol/L)、KN-93(500 nmol/L)、CA(10 nmol/L)处理分别设置为伊伐布雷定+H89处理组、KN-93处理组、CA处理组(n=6)。采用场刺激诱导心肌细胞钙瞬变,测定伊伐布雷定及分别在H89、KN-93及CA干预下对钙释放的作用。给药的方法及浓度同体外心脏实验。结果给药A组左心室发展压[(109.86±11.65)mmHg]、心输出量[(36.27±2.22)mL/min]、收缩压[(108.57±9.24)mmHg]均较空白A组[(102.43±11.06)mmHg、(33.72±1.96)mL/min、(99.74±8.67)mmHg]增加(P<0.01),心率[(324.17±11.33)次/min]较空白组[(348.56±10.02)次/min)]降低(P<0.01)。给药B组LVDP[(144.05±5.75)mmHg]、左心室肌细胞钙释放的幅值[(118.06±16.81)]较空白B组[(100.00±7.68)mmHg、(100.00±8.42)]明显增加(P<0.01)。H89处理组及KN-93处理组左心室发展压、左心室肌细胞钙释放的幅值显著低于其对照组(P<0.01),CA处理组较CA对照组显著增加(P<0.01)。结论伊伐布雷定可通过CaMKII靶点发挥其正性肌力作用。

Objective Ivabradine reduces heart rate by inhibiting I f current of cardiomyocyte and is used clinically to treat stable angina pectoris and myocardial ischemia.However,the mechanism of positive inotropic effect by Ivabradine is still not well understood.This study aims to investigate the Ivabradine's positive inotropic effect both in vivo and in vitro and the underlying mechanism involved.Methods①A Millar catheter with double-pressure was inserted into the right carotid artery of general anesthesia rats.The pressure-volume of left ventricle,HR(heart rate)and aortic pressure were recorded as a blank group(n=7).The effect of Ivabradine(1 mg/kg)administrated via left external jugular vein was recorded as a drug treated group(n=7).The cardiac output,left ventricular and aortic pressure of the rats in the blank group A and the administration group A were compared,and the results were used to analyze the Ivabradine's inotropic effect in vivo.②Langendorff setup was used to analyze the left ventricular pressure of the isolated heart.The normal perfusion solution was used as the blank group(n=6),while the Ivabradine(10μmol/L)perfusion was used as the treated group(n=6).In addition,the treatment of H89(200 nmol/L)(a PKA inhibitor)was recorded as the blank group(n=6)and the combined use of H89(200 nmol/L)and Ivabradine(10μmol/L)was recorded as drug treated group(n=6).Following the above protocol,KN-93(500 nmol/L)(a CaMKII inhibitor)or CA(10 nmol/L)(a protein phosphatase 1 and 2A inhibitor)was used to analyze the inhibitory effect on inotropic effect of Ivabradine(n=6 for each group).③The field stimulation induced Ca^2+ transient from cardiomyocyte was used to investigate the mechanism underlying the positive inotropic effect of Ivabradine(10μmol/L).The perfusion orders and concentrations of Ivabradine or/and H89,KN-93 and CA were the same as that in isolated rat heart experiment(n=6 for each group).Results①Ivabradine(1 mg/kg)significantly increased the left ventricular develop pressure(from 102.43±11.06 in blank group to 109.86±11.65 mmHg in ivabradine treated group,P<0.01,n=7)and cardiac output(from 33.72±1.96 in blank group to 36.27±2.22 mL/min in ivabradine treated group,P<0.01,n=7).It reduced the heart rate(from 348.56±10.02 in blank group to 324.17±11.33 beats/min in ivabradine treated group,P<0.01,n=7)and increased the systolic blood pressure(from 99.74±8.67 in blank group to 108.57±9.24 mmHg in Ivabradine treated group,P<0.01,n=7)without significant change in diastolic blood pressure.②Ivabradine(1,10μmol/L)significantly increased the left ventricular developed pressure(LVDP)(P<0.05,n=6).The positive inotropic effect of Ivabradine was blocked by CaMKⅡinhibitor of KN-93.③Ivabradine(10μmol/L)significantly increased the amplitude of SR Ca^2+ transient(P<0.01,n=6).The enhanced amplitude of Ca^2+ transient was blocked by CaMKⅡinhibitor of KN-93.Conclusion Ivabradine shows a positive inotropic effect in rat hearts both in vivo and in vitro and its underlying mechanism involved the action which was mediated by CaMKⅡ.