Cellular mechanisms of cardioprotection by ischemic preconditioning : Functional study using Kir6.2- (Kir6.2^<-/->) and Kir6.1-deficient (Kir6.1^<-/->) mice

为了阐明心肌细胞膜ATP敏感性K^+（sarcK_<ATP>）通道在心脏和血管平滑肌细胞中的病理生理作用，我们用Kir6.2^&lt;-/-&gt;和Kir6.1 ^&lt;-/-&gt;小鼠进行了功能实验，在Kir6.2 ^&lt;-/-&gt;小鼠心室肌细胞中，sarcK_<ATP>通道功能被否定，但线粒体K_<ATP>（mitoK_<ATP>）通道功能被保留，通过二氮氧化物诱导的黄素蛋白氧化来评估。缺血预处理（IPC）实验在麻醉小鼠长期缺血（45 min）之前，阻断冠状动脉3 min，再灌注5 min。IPC减少了野生型（WT）小鼠的梗死面积，但在Kir6.2^&lt;-/-&gt;小鼠中没有。Kir6.2^&lt;-/-&gt;小鼠Langendorff灌流心脏在全脑缺血/再灌注后左心室收缩功能的恢复比WT心脏差。结果表明，sarcK_<ATP>通道在缺血预适应的建立和缺血/再灌注后机械功能的恢复中起重要作用<ATP>。尽管<ATP><ATP>Kir6.1^&lt;-/-&gt;小鼠心肌细胞的sarcK_和mitoK_通道功能得以保留，但Kir6.1 <ATP>^&lt;-/-&gt;小鼠血管平滑肌细胞的sarcK_通道对K^+通道开放剂的功能反应受到损害。特别令人感兴趣的是Kir6.2^&lt;-/-&gt;小鼠显示出与自发性ST段抬高相关的高心脏性猝死率，随后是ECG上的房室传导阻滞。上述结果提示，Kir6.1在调节血管张力，尤其是冠状动脉张力中起重要作用，而钾通道功能障碍<ATP>是导致Prinzmetal型心绞痛的原因，因此Kir6.2或Kir6.1对心血管系统中sarcK通道的功能起着绝对重要<ATP>的作用。

In order to clarify the pathophysiological roles of sarcolemmal ATP-sensitive K^+ (sarcK_<ATP>) channel in cardiac and vascular smooth muscle cells, we conducted functional experiments using Kir6.2-deficient (Kir6.2^<-/->) and Kir6.1-deficient (Kir6.1^<-/->) mice.In ventricular cells of Kir6.2^<-/-> mice sarcK_<ATP> channel function was negated but the mitochondrial K_<ATP> (mitoK_<ATP>) channel function, evaluated by diazoxide-induced flavoprotein oxidation, was preserved. For ischemic preconditioning (IPC) experiments coronary artery was occluded for three periods of 3 min, each followed by 5 min reperfusion, before the long-term ischemia (45 min) in anesthetized mice. IPC reduced the infarct size in wild-type (WT) mice but not in Kir6.2^<-/-> mice. The recovery of the left ventricular contractile function after global ischemia/reperfusion was worse in Langendorff-perfused hearts of Kir6.2^<-/-> mice than in WT hearts. These findings indicate that sarcK_<ATP> channel is important for the establishment of ischemic preconditioning and the recovery of mechanical function after ischemia/reperfusion.We also evaluated sarcK_<ATP> channel function in cardiac and vascular smooth muscle cells of Kir6.1^<-/-> mice. Although both sarcK_<ATP> and mitoK_<ATP> channel function were preserved in cardiac cells of Kir6.1^<-/-> mice, functional responses of sarcK_<ATP> channels to K^+ channel openers were impaired in vascular smooth muscle cells of Kir6.1^<-/-> mice. Of particular interest are the findings that Kir6.2^<-/-> mice showed a high rate of sudden cardiac death associated with spontaneous ST elevation followed by atrioventricular block on ECG. These results suggest that Kir6.1 is critical in the regulation of vascular tone, especially in the coronary arteries, and the dysfunction of the K_<ATP> channel causes Prinzmetal angina.Thus, either Kir6.2 or Kir6.1 is absolutely important for the function of sarcK_<ATP> channels in the cardiovascular system.