Differential Effects of Sarcolemmal and Mitochondrial KATP Channels Activated by 17 -Estradiol on Reperfusion Arrhythmias and Infarct Sizes in Canine Hearts

We have demonstrated the effects of estrogen on modulation of ATP-sensitive K channels; however, the subcellular location of these channels is unknown. The purpose of the present study was to investigate the role of the sarcolemmal and mitochondrial ATP-sensitive K channels in a canine model of myocardial infarction after stimulation with 17 -estradiol. Anesthetized dogs were subjected to 60 min of the left anterior descending coronary artery occlusion followed by 3 h of reperfusion. Infarct size was markedly reduced in estradiol-treated dogs compared with controls (14 6 versus 42 6%, P 0.0001), indicating the effective dose of estradiol administrated. Pretreatment with the mitochondrial ATP-sensitive K channel antagonist 5-hydroxydecanoate completely abolished estradiol-induced cardioprotection. The sarcolemmal ATP-sensitive K channel antagonist 1-15-12-(5-chloro-o-anisamido)ethylmethoxyphenyl)sulfonyl-3-methylthiourea (HMR 1098) did not significantly attenuate estradiol-induced infarct size limitation. In addition, estradiol administration significantly reduced the incidence and duration of reperfusion-induced ventricular tachycardia and ventricular fibrillation. Although 5-hydroxydecanoate alone caused no significant effect on the incidence of reperfusion arrhythmias in the presence or absence of estradiol, the administration of HMR 1098 abolished estrogen-induced improvement of reperfusion arrhythmias. Pretreatment with the estrogen-receptor antagonist faslodex (ICI 182,780) did not alter estrogen-induced infarct-limiting and antiarrhythmic effects. These results demonstrate that estrogen is cardioprotective against infarct sizes and fatal reperfusion arrhythmias by different ATP-sensitive K channels for an estrogen receptor-independent mechanism. The infarct size-limiting and antiarrhythmic effects of estrogen were abolished by 5-hydroxydecanoate and HMR 1098, suggesting that the effects may result from activation of the mitochondrial and sarcolemmal ATP-sensitive K channels, respectively. Epidemiological studies showed that women appear to have a lower incidence of arrhythmia-related sudden death than men (Sourander et al., 1998). Estrogen can decrease cardiovascular mortality primarily in sudden cardiac death in postmenopausal women (Sourander et al., 1998). However, the mechanism involved is not completely known. Fatal reperfusion arrhythmia occurring in the absence of heart failure or hypotension is a common complication of acute myocardial infarction (Volpi et al., 1987). Estrogen has been shown previously to attenuate reperfusion-induced ventricular arrhythmias in the dog (McHugh et al., 1995). The antiarrhythmic effects of estrogen have been attributed to antioxidants (McHugh et al., 1998), resulting in a reduction of free radicals during reperfusion. We have previously demonstrated that there is an association of estrogen and ATPsensitive K channels in patients with syndrome X by analyzing the changes of electrocardiographic QT parameters (Lee et al., 1999). However, no previous study has addressed this issue on the effects of estrogen on ATP-sensitive K channels and the incidence of arrhythmias during myocardial reperfusion. Cardioprotection via ATP-sensitive K channels may be an integral player in ischemic preconditioning (IP), where brief periods of ischemia and reperfusion before a sustained ischemic stress protects the heart. We have previously demonstrated that estrogen can activate mitochondrial ATP-sensitive K (mit-KATP) channels and mimicked IP to reduce myocardial infarct size in anesthetized dogs (Lee et al., 2000). Cardiac myocytes contain two distinct ATP-sensitive K channels with one subtype located in the sarcolemma (sarKATP) and the other in the inner membrane of the mitochondria (mit-KATP) (Liu et al., 2001). mit-KATP channels share This work was supported by Grant NSC89-2314-B002-186 from the National Science Council, (Taiwan, Republic of China) and by Grant NTUH89S1026 from National Taiwan University Hospital. ABBREVIATIONS: IP, ischemic preconditioning; mit-KATP, mitochondrial KATP; sar-KATP, sarcolemmal KATP; VF, ventricular fibrillation; VT, ventricular tachycardia; HMR 1098, 1-15-12-(5-chloro-o-anisamido)ethyl-methoxyphenyl)sufonyl-3-methylthiourea; ICI 182,780, faslodex. 0022-3565/02/3010-234–240$7.00 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 301, No. 0 Copyright © 2002 by The American Society for Pharmacology and Experimental Therapeutics 4202/974293 JPET 301:234–240, 2002 Printed in U.S.A. 234 at A PE T Jornals on July 5, 2017 jpet.asjournals.org D ow nladed from some pharmacological properties with sar-KATP channels while possessing a distinct pharmacological response. sarKATP channels are selectively blocked by HMR 1098, whereas mit-KATP channels are specifically inhibited by 5-hydroxydecanoate (Liu et al., 2001). The involvement of the two types of ATP-sensitive K channels in estradiol-induced infarct size and antiarrhythmias during ischemic and reperfusion remained unknown. Although there is an emerging consensus that the activation of mit-KATP channels reduces infarct size, there are widely divergent views regarding whether sarKATP channels act in an antiarrhythmic role during reperfusion. Activation of sar-KATP channels can theoretically be antiarrhythmic, because shortening of the action potential duration by opening these channels would suppress triggered activity, which is an important mechanism of reperfusion arrhythmias (Wilde and Janse, 1994). However, several studies have demonstrated a decrease in arrhythmic severity with ATP-sensitive K channel blockers (Dhein et al., 2000). This discrepancy may stem from different species (dogs, pigs, rabbits, rats), collateral flow measurements (microspheres versus others), model studies (isolated heart versus in vivo), and different arrhythmic quantitative methods (arrhythmic score versus incidence) used in the studies. Small animals did not provide a good model to assess the pharmacological effects on arrhythmias because their hearts are too small to sustain arrhythmias (Sakamoto et al., 1999). Such tests are performed better in large animals. Thus, this study investigated whether pretreatment with 17 -estradiol in physiological concentrations provides cardioprotection against infarct size and fatal reperfusion arrhythmias in a canine model of acute myocardial infarction. We have also investigated whether the observed antinecrotic and antiarrhythmic effects of 17 -estradiol are due to the activation of mitand sar-KATP channels by the use of 5-hydroxydecanoate and HMR 1098, specific mitand sar-KATP channel blockers, respectively. Besides, to assess whether the estrogen-induced effects are related to activation of estrogen receptors, we used a specific estrogen receptor antagonist ICI 182,780. Materials and Methods