Cardioprotective Effect of Diazoxide Is Mediated by Activation of Sarcolemmal but Not Mitochondrial ATP-Sensitive Potassium Channels in Mice

Abstract

Background-We recently demonstrated that the sarcolemmal ATP-sensitive potassium (sarcK ATP ) channel plays a key role in cardioprotection against ischemia/reperfusion injuries in Kir6.2-knockout (KO) mice. In the present study, we evaluated the effects of diazoxide, a mitochondrial ATP-sensitive potassium (mitoK ATP ) channel opener, on ischemiainduced myocardial stunning in sarcK ATP channel-deficient mice. Methods and Results-Langendorff-perfused hearts of wild-type (WT) and KO mice were subjected to global ischemia/reperfusion. Diazoxide improved the recovery of contractile function in WT hearts but not in KO hearts. Treatment with HMR1098 (a sarcK ATP channel blocker) but not 5-hydroxydecanoate (a mitoK ATP channel blocker) abolished the cardioprotective effect of diazoxide in WT hearts. In coronary-perfused WT ventricular muscle preparations, action potential shortening during ischemia was accelerated in the presence of diazoxide. Key Words: potassium Ⅲ ischemia Ⅲ reperfusion Ⅲ ion channels A TP-sensitive potassium (K ATP ) channels play an important role in cardiovascular system. Our recent study using Kir6.2-deficient (KO) mice revealed that Kir6.2 forms the pore region of the cardiac sarcolemmal K ATP (sarcK ATP ) channel but not that of the vascular sarcK ATP channel. 1,2 In addition, neither Kir6.2 nor Kir6.1 seems to be a constituent of the mitochondrial K ATP (mitoK ATP ) channel in cardiomyocytes, 2,3 as assessed by flavoprotein oxidation assay. Recently, it was postulated that activation of mitoK ATP channels rather than sarcK ATP channels is important in cardioprotection against ischemia/reperfusion injuries, and that diazoxide and 5-hydroxydecanoate (5-HD) are a mitoK ATP -specific opener and blocker, respectively. 4 -9 This conclusion was based on pharmacological data, however, and the molecular identity of the mitoK ATP channel has not been established. Conclusions-DiazoxideWe recently found that ischemic preconditioning is abolished in sarcK ATP channel-deficient mice despite intact mitoK ATP channel function. 3 It is unclear whether diazoxide can exert cardioprotective effect, however, even if the sarcK ATP channel is negated. In the present study, we performed functional analysis of wild-type (WT) and knockout (KO) mouse hearts subjected to ischemia/reperfusion, and we show that the activity of the sarcK ATP channel is essential for diazoxide-induced anti-stunning effect, possibly caused by the reduced cardiac excitability when they are open. Methods Kir6.2 -/-MiceAll procedures complied with National Institutes of Health standards for the care and use of animal subjects. A mouse line deficient in K ATP channels was generated by targeted disruption of the gene coding for Kir6.2, as described previously. 10 C57BL/6 mice from our laboratory were used as controls because the knockout animals had been backcrossed to a C57BL/6 strain for 5 generations. In Vitro Functional Study Using Langendorff-Perfused HeartsFunctional study using isolated mouse hearts was performed as previously described. 1,...

Benefit of nicorandil using an immunologic murine model of experimental colitis

“…One suggested mechanism for the antioxidant activity characteristics of nicorandil is the role of mt-KATP channels. Although some investigations suggest that mt-KATP channels have a role in ischemic preconditioning, especially in intestinal tissue [24], there are others who question this property [45,46]. For instance, one suggested mechanism to explain ischemic preconditioning in cardiac tissue is involvement of sarcolemmal KATP channels rather than mt-KATP channels.…”

Mitochondrial K channels in cell survival and death

“…This issue was recently readdressed in Kir6.2 knockout mice [71,72]. The knockout mice displayed a blunted response to IPC, and their hearts went into contracture within 5 min of exposure to ischemia and did not recover function during reperfusion.…”

Cardioprotective Effect of Diazoxide Is Mediated by Activation of Sarcolemmal but not Mitochondrial ATP-Sensitive Potassium Channels in Mice

“…We thank Drs Duncker and Verdouw for their interest in our article 1 and their comments with respect to the interpretation of the results.…”

“…The findings of the study suggested that activation of sarcolemmal K ATP channels rather than mitochondrial K ATP channels is important for the cardioprotective effect of diazoxide in mouse hearts. 1 We measured the left ventricular function during 20-minute ischemia followed by 60-minute reperfusion and found that diazoxide improved the contractile dysfunction in wildtype but not Kir6.2 knockout hearts. The stunned myocardium is defined as "prolonged postischemic contractile dysfunction of myocardium salvaged by reperfusion."…”