“缺血”心肌起搏离子流I_f的观察研究

AN OBSERVATION ON THE PACEMAKER CURRENT I_f IN SHEEP CARDIAC PURKINJE FIBERS UNDER ISCHEMIA-MIMIC CONDITION

本文观察“缺血”及肾上腺素能激动剂对绵羊心室浦肯野纤维起搏离子流Ｉｆ的影响。用模拟缺血溶液灌流１５，３０和６０ｍｉｎ后，在Ｅｃ—６０ｍＶ—１２０ｍＶ之间的各不同指令电位水平Ｉｆ离子流幅值均降低（ｎ＝７，Ｐ＜０．０５），激活达稳态时间及半激活时间延长（ｎ＝７，Ｐ＜Ｏ．０５），激活曲线向超极化方向移位。１×１０－６ｍｏｌ／Ｌ异丙基肾上腺素能使Ｉｆ离子流幅值增加（ｎ＝１０，Ｐ＞０．０５），激活达稳态时间及半激活时间缩短（ｎ＝１０，Ｐ＜０．０５），激活曲线向除极化方向移位，但不能完全逆转“缺血”对Ｉｆ离子流的抑制作用。在５×１０－７ｍｏｌ／Ｌ普萘洛尔存在条件下，５×１０－５ｍｏｌ／Ｌ新福林对正常绵羊心室浦肯野纤维Ｉｆ离子流影响不一致，但可加剧“缺血”对Ｉｆ离子流的抑制作用。上述结果表明：急性心肌缺血时，心室浦肯野纤维正常起搏活动不是增强，而是减弱。提示急性缺血性室性心律失常不是由于心室正常自律活动异常增强引起。

Effects of 'ischemia' and edrenergic agonists on pacemaker current If were observed in sheep cardiac Purkinje fibers. After perfusion with ischemia-mimic solution for 15, 30 and 60 min, the amplitllde of If current were decreased at all membrane potential levels between Ec-60 mV to-120 mV (n=7, P< 0. 05), activation time and half activation time to a steady state value of If current were prolonged (n=7, P<0. 05), activation curve of If shifted to a more hyperpolarized position. Isoproterenol 1×10-6 mol/L increased amplitude of if current (n=10, P<0. 05), shortened the aotivation time and half activation time (n=10, P>0. 05), and Shifted the activation curve to a more depolarized position; but isoptoterenol of 1×10-6 mol/L could not completely reverse the inhibitoty effects of 'ischemian' on If current. In the presence of 5×10-7mol/L propranolol the effects of phenylephrine 5 × 10-5mol/L on If current was variable ; but aggravated the inhibitory effects of If current due to 'ischemia'. The above results indicate that normal pacemaker activity of ventricular Purkinje fibers doesnot increase but rather decrease during myocardial ischemia-mimic condition, an observation suggesting that acute ischemic ventricular arrhythmia may not be due to abnormal strengthening of normal ventricuinr pacemaker activity.