Anti-arrhythmic Effect Of κ-opioid Receptor In Myocardium Of Rats With Ischemia And Reperfusion And Its Potential Mechanism

Endogenous opioid peptides (EOPs) and opioid receptors, which widely exist in diverse systems, play important roles in central analgesia as well as in the regulation of cardiovascular functions. Opioid receptors are found rich on the membrane of cardiac myocytes and in blood vessel wall,at the mean time, heart itself is found capable of producing EOPs, which suggests that opioid peptides act on the cardiovascular system. Our study showed that activation ofк-opioid receptor during myocardial ischemia and reperfusion in rats induced an anti-arrhythmic effect in vivo, as well as in vitro. However, it is not clear so far whether there is alters in the opioid receptor system under the condition of myocardial ischemia. Further study of EOPs and opioid receptors would hopefully build the theoretical foundation of treating arrhythmia induced by coronary artery ischemia with opioid in clinic.1. Objectives:(1) To observe the expression ofк-opioid receptor in myocardial ischemia and reperfusion in rats.(2) We use U50,488H (a selectiveк-opioid receptor agonist) and nor-BNI (a selectiveк-opioid receptor antagonist) to investigate the anti-arrhythmic effect ofк-opioid receptor during myocardial ischemia and reperfusion in rats.(3) To investigate the possible signal pathway involved in the anti-arrhythmic effect ofк-opioid receptor during myocardial ischemia and reperfusion by using pertussis toxin (a Gi/o protein inhibitor), glibenclamide (an ATP-sensitive potassium channel blocker), chelerythrine (a selective PKC inhibitor) and genistein (a Tyrosine kinase inhibitor).2. Methods:(1) Male Sprague-Dawley rats weighing 220～300 g were used for all experiments. The rats were randomly divided into different groups according to experiment protocol. Parameters of heart function were recorded during the myocardial ischemia and reperfusion injuries, and the tissue of heart was kept for afterwards analysis.(2) The RT-PCR technique was used to investigate the content ofк-opioid receptor mRNA in rat at different time point during ischemia and reperfusion.(3) The WESTERN BLOT technique was used to investigate the density ofк-opioid receptor protein in rat at different time point during ischemia and reperfusion.3. Results:(1) The changes ofк-opioid receptor gene and protein at the different time during ischemia and reperfusion:①compared with control group, the content ofк-opioid receptor mRNA was increased significantly at 0 min, 60 min and 180 min during reperfusion (P<0.01), and was decreased to the normal level at 360 min.②compared with control group, the density ofк-opioid receptor protein was increased significantly at 0 min, 60 min, 180 min and 360 min during reperfusion (P<0.05).(2) Anti-arrhythmic effects induced byк-opioid receptor activation: Few ventricular premature contractions were observed in the rats control group. After left anterior descending coronary artery (LAD) occlusion, ventricular premature contractions, ventricular tachycardia and ventricular fibrillation were examined by electrocardiogram. In the course of reperfusion, much more ventricular arrhythmia appeared especially at the immediate time of reperfusion. Finally, the incidence of ventricular arrhythmia was reduced with the development of reperfusion. With the pretreatment of U50,488H, the endurances of ventricular arrhythmia in the rats of U50,488H+ischemia/reperfusion (U50,488H+I/R) group were significantly shortened, and the incidence of ventricular arrhythmia was reduced as well as the arrhythmia score (P<0.01). With the pretreatment of nor-BNI for 15 min in U50,488H+I/R group, the anti-arrhythmic effect of U50,488H was completely blocked (P<0.01). But it had no effect on the arrhythmia induced by ischemia and reperfusion in I/R group (P>0.05).(3) The influence of inhibitors of Gi/o protein, PKC and Tyrosine kinase, ATP-sensitive potassium channel blocker on the anti arrhythmic effect ofк-opioid receptor activation: Pretreated with pertussis toxin, glibenclamide and chelerythrine respectively, the anti-arrhythmic effects induced by U50,488H during myocardial ischemia and reperfusion were significantly attenuated or even were completely blocked (P<0.05). The anti-arrhythmic effects of U50,488H were not significantly affected by pretreatment with genistein(P>0.05).4. Conclusions(1) Our study finds that the increasing expression ofк-opioid receptor is induced by the myocardial ischemia and reperfusion for the first time. And it is helpful for the EOPs to act the anti-arrhythmia effect during myocardial ischemia and reperfusion. This may be a compensational mechanism of heart's self-protection.(2) U50,488H exerts an anti-arrhythmic effect through activatingк-opioid receptor in the rats with myocardial ischemia and reperfusion. The signal pathway may be correlated with Gi/o, PKC and KATP channel.