The potassium channel activators cromakalim and pinacidil were recently shown to have anti-ischemic properties in isolated globally ischemic rat hearts. The effects of two reported blockers of ATP-sensitive potassium channels, glibenclamide (glyburide) and sodium 5-hydroxydecanoate, on the anti-ischemic efficacy of cromakalim were determined in this model. Buffer-perfused rat hearts were subjected to 25 minutes of ischemia followed by 30 minutes of reperfusion. Pretreatment of these hearts with 60-mu-M cromakalim significantly decreased indexes of contractile function but caused a significant improvement of postreperfusion function and a significant decrease in release of lactate dehydroxygenase and in end-diastolic pressure. Pretreatment with glibenclamide at concentrations that reversed the preischemic effects of cromakalim (0.05 and 1.0-mu-M) also significantly reversed its postischemic protective effects. Sodium 5-hydroxydecanoate (100 and 300-mu-M) had no effect on the preischemic (negative inotropic) effects of cromakalim but completely reversed its cardioprotective effects. Sodium 5-hydroxydecanoate did not reverse the cardioprotective effects of the calcium entry blocker diltiazem. In phenylephrine-contracted rat aorta, glibenclamide (0.1-10-mu-M) inhibited cromakalim-induced relaxation, whereas sodium 5-hydroxydecanoate (10-1,000-mu-M) had no effect. Similarly, the ability of cromakalim to shorten cardiac action potential duration in guinea pig papillary muscle and to increase outward whole-cell potassium currents in isolated myocytes was inhibited by glibenclamide, whereas sodium 5-hydroxydecanoate was without effect. Thus, both glibenclamide and sodium 5-hydroxydecanoate inhibited the effects of cromakalim after reperfusion; however, sodium 5-hydroxydecanoate, unlike glibenclamide, had no effect in nonischemic preparations. These results suggest that sodium 5-hydroxydecanoate is an ischemia-selective inhibitor of ATP-sensitive potassium channels.
