Block of Cardiac ATP-Sensitive K+ Channels Reduces Hydroxyl Radicals in the Rat Myocardium

Abstract

The present study examined whether opening of an ATP-sensitive K+ (KATP) channel can induce hydroxyl free radical (•OH) generation in the rat myocardium. Sodium salicylate in Ringer's solution (0.5 nmol/μl/min) was infused directly through a microdialysis probe to detect the generation of •OH as reflected by the nonenzymatic formation of 2,3-dihydroxybenzoic acid (DHBA). Induction of cromakalim (100 μM), a KATP channel opener, through the microdialysis probe significantly increased the level of 2,3-DHBA. Another KATP channel opener, nicorandil, also increased the level of 2,3-DHBA. When iron(II) was administered to cromakalim-pretreated animals, a marked elevation of DHBA was observed, compared with iron(II) only-treated animals. A positive linear correlation between iron(II) and formation of •OH, trapped as DHBA in the dialysate, was shown (r2 = 0.988). When corresponding experiments were performed with nicorandil-treated animals, a positive linear correlation between iron(II) and DHBA in the dialysate was shown (r2 = 0.988). However, the presence of glibenclamide (1–50 μM) decreased the cromakalim-induced 2,3-DHBA formation in a concentration-dependent manner (IC50 = 9.1 μM). 5-Hydroxydecanoate (5-HD; 100 μM), another KATP channel antagonist, also decreased cromakalim-induced •OH formation. The IC50 value for 5-HD against cromakalim-evoked increase in 2,3-DHBA was 107.2 μM. In the presence of glibenclamide (10 μM), the heart was subjected to myocardial ischemia for 15 min by occlusion of the left anterior descending coronary artery (LAD). When the heart was reperfused, the normal elevation of 2,3-DHBA in the heart dialysate was not observed in animals pretreated with glibenclamide (10 μM). When corresponding experiments were performed with 5-HD (100 μM) pretreated animals, the same results were obtained. These results suggest that opening of cardiac KATP channels may cause •OH generation.