KATP channels and memory of ischemic preconditioning in dogs: synergism between adenosine and KATP channels

Results from numerous studies have shown that there is an important link between adenosine A1 receptors and ATP-sensitive potassium (KATP) channels in mediating the cardioprotective effects of ischemic preconditioning (PC). The major aim of the present study was to determine whether occupation of A1 receptors and/or the opening of KATP channels is involved in the time delay between the PC stimulus and the prolonged ischemic insult or the "memory" of PC to reduce infarct size. Barbital sodium-anesthetized dogs were subjected to 1 h of left anterior descending coronary artery (LAD) occlusion followed by 4 h of reperfusion. Ischemic PC was elicited by 10 min of LAD occlusion followed by 1 h of reperfusion (1-h memory) before the 1-h occlusion period. Either adenosine (800 g/min), bimakalim (3 g/min), a combination of two lower doses of each agent (400 g/min of adenosine and 0.3 g/min of bimakalim), or an equivalent volume of saline was infused into the LAD for 10 min followed by a 1-h drug-free period before the 1-h ischemic insult. In another series, glibenclamide, 8-cyclopentyl-1,3-dipropylxanthine (a selective A1-receptor blocker), or PD-115199 (a nonselective adenosine-receptor antagonist) was administered 50 min after ischemic PC (10 min before the 1-h occlusion period). Infarct size (IS) was expressed as a percentage of the area at risk. PC with 1 h of reperfusion resulted in a marked reduction in IS (8.1 +/- 6.5 vs. 29.8 +/- 5.8% in control dogs). Administration of adenosine or bimakalim followed by a 1-h drug-free period had no effect on IS; however, the simultaneous administration of adenosine and bimakalim resulted in a marked decrease in IS (11.5 +/- 2.7%). One hour after ischemic PC, administration of glibenclamide blocked the protective effect of ischemic PC, whereas 8-cyclopentyl-1,3-dipropylxanthine or PD-115199 did not affect it. These results provide evidence that the opening of myocardial KATP channels may play an important role in the memory of ischemic PC in the canine heart and also suggest that adenosine and the KATP channel may have a synergistic interaction that is important for the memory phase of PC.