Effect of ischemic preconditioning on cardiac function and mitochondrial K_(ATP) channel of isolated heart following ischemia- reperfusion in rats

Objective To investigate the role of mitochondrial KATP channel in the mechanism of the protective effect of ischemic preconditioning (IP) against ischemia-reperfusion (I/R) injury.Methods Forty-eight Wistar rats of both sexs weighing 250-350 g were used in this study. Forty rats were randomly divided into 5 groups ( n = 8 each): group A I/R; group B IP+ I/R; group C diazoxide (DZ mito-KATP channel activator) + I/R; group D 5-HD (mito-KATP channel blocker) + IP + I/R and group E 5-HD + DZ + I/R. Another 8 animals were used for electron microscopic examination of normal mitochondria as control. The animals were anesthetized with intraperitoneal pentobarbital 30 mg·kg-1. The hearts were immediately excised and passively perfused in a Langendorff apparatus with K-H solution at 5.8 kPa perfusion pressure and 36.5-37.5℃ via aortic cannulation. A fluid-filled latex balloon was via left atrium in left ventricle for the measurement of left ventricular function. I/R was induced after 30 min stabilization by clamping aortic cannula for 40 min followed by 30 min reperfusion. In group B and D the isolated hearts underwent 2 episodes of 5 min ischemia followed by 5 min reperfusion before I/R. In group C and E DZ 50 μmol·L-1 was infused for 10 min and in group D and E 5-HD 100 μmol·L-1 was infused for 10 min before I/R. HR, LVSP, LVEDP and coronary flow (CF) were measured at the end of stabilization (T0 , baseline), immediately before I/R (T1 ) and at 10, 20 and 30 min of reperfusion (T2.3.4.), and left ventricular developed pressure (LVDP= LVSP- LVEDP) was calculated. Myocardial tissue was obtained at the end of 30 min reperfusion for electron microscopic examination of mitochondria. Mitochondrial ultrastructure was assessed by Flameng scoring system (0 = normal, 4 = severely damaged) .Results Ischemic and DZ preconditioning significantly increased LVDP and decreased LVEDP and Flameng score. 5-HD pretreatment partly antagonized the protective effect of IP and completely antagonized that of DZ against I/R injury. Conclusion Ischemic preconditioning protects the heart against I/R injury mainly by activating mitochondrial KATP channel.