Specific block of the anti-ischemic actions of cromakalim by sodium 5-hydroxydecanoate.

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Abstract
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 microM 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 microM) also significantly reversed its postischemic protective effects. Sodium 5-hydroxydecanoate (100 and 300 microM) 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 microM) inhibited cromakalim-induced relaxation, whereas sodium 5-hydroxydecanoate (10-1,000 microM) 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.