Distinct roles for sarcolemmal and mitochondrial adenosine triphosphate-sensitive potassium channels in isoflurane-induced protection against oxidative stress

Background: Cardiac preconditioning, including that induced by halogenated anesthetics, is an innate protective mechanism against ischemia-reperfusion injury. The adenosine triphosphate-sensitive potassium (K-ATP) channels are considered essential in preconditioning mechanism. However, it is unclear whether K-ATP channels are triggers initiating the preconditioning signaling, and/or effectors responsible for the cardioprotective memory and activated during ischemia-reperfusion. Methods: Adult rat cardiomyocytes were exposed to oxidative stress with 200 mu m H2O2 and 100 gm FeSO4. Myocyte survival was determined based on morphologic characteristics and trypan blue exclusion. To induce preconditioning, the myocytes were pretreated with isoflurane. The involvement of sarcolemmal and mitochondrial KAY channels was investigated using specific inhibitors HMR-1098 and 5-hydroxydecanoic acid. Data are expressed as mean +/- SD. Results: Oxidative stress induced cell death in 47 +/- 14% of myocytes. Pretreatment with isoflurane attenuated this effect to 26 +/- 8%. Blockade of the sarcolemmal K-ATP channels abolished the protection by isoflurane pretreatment when HMR-1098 was applied throughout the experiment (50 +/- 21%) or only during oxidative stress (50 +/- 12%), but not when applied during isoflurane pretreatment (29 +/- 13%). Inhibition of the mitochondrial K-ATP channels abolished cardioprotection irrespective of the timing of 5-hydroxydecanoic acid application. Cell death was 42 +/- 23, 45 +/- 23, and 46 +/- 22% when 5-hydroxydecanoic acid was applied throughout the experiment, only during isoflurane pretreatment, or only during oxidative stress, respectively. Conclusion: The authors conclude that both sarcolemmal and mitochondrial K-ATP channels play essential and distinct roles in protection afforded by isoflurane. Sarcolemmal K-ATP channel seems to act as an effector of preconditioning, whereas mitochondrial K-ATP channel plays a dual role as a trigger and an effector.