Positive inotropic effect of Ivabradine in rats and its underlying mechanism / 医学研究生学报

ABSTRACT

ObjectiveIvabradine reduces heart rate by inhibiting If 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 effectin 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 (10 μmol/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 (10 μmol/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 Ca2+ transient from cardiomyocyte was used to investigate the mechanism underlying the positive inotropic effect of Ivabradine (10 μmol/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).Results① Ivabradine (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. ② Ivabradine (1, 10 μmol/L) significantly increased the left ventricular developed pressure (LVDP) (P<0.05, n=6). The positive inotropic effect of Ivabradine was blocked by CaMKⅡ inhibitor of KN-93. ③ Ivabradine (10 μmol/L) significantly increased the amplitude of SR Ca2+ transient (P<0.01,n=6). The enhanced amplitude of Ca2+ transient was blocked by CaMKⅡ inhibitor of KN-93.ConclusionIvabradine 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.