Diverse roles of KATP channels learned from Kir6.2 genetically engineered mice
Diverse roles of KATP channels learned from Kir6.2 genetically engineered mice
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DOI：
10.2337/diabetes.49.3.311
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发表时间：
2000-03-01
期刊：
影响因子：
7.7
通讯作者：
Miki, T
中科院分区：
文献类型：
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作者：
Seino, S;Iwanaga, T;Miki, T
胰腺β细胞分泌胰岛素的调节主要取决于其质膜离子通道的活性。ATP敏感性K+通道（K-ATP通道）存在于许多细胞中，通过细胞代谢与膜电位的偶联来调节细胞的多种功能。胰腺β细胞中K-ATP通道的活性受葡萄糖代谢引起的ATP和ADP浓度（ATP/ADP比值）变化的调节。因此，K-ATP通道是葡萄糖诱导的胰岛素分泌调节中的ATP和ADP传感器。K-ATP通道也是磺酰脲类药物的靶点，磺酰脲类药物广泛用于治疗2型糖尿病。胰腺β细胞K-ATP通道的两个亚基Kir6.2（内向整流K+通道成员）和SUR 1（磺酰脲类药物受体）的分子克隆为其结构和功能提供了很好的见解。Kir6.2亚基形成K+离子渗透孔，主要通过ATP抑制通道，而SUR 1亚基通过MgADP和K+通道开放剂（如二氮嗪）激活通道，以及通过磺酰脲类抑制。为了直接确定K-ATP通道的生理作用，我们产生了两种基因工程小鼠：在胰腺β细胞中特异性表达Kir6.2的显性阴性形式的小鼠（Kir6.2G132S Tg小鼠）和缺乏Kir6.2的小鼠（Kir6.2敲除小鼠）。对这些小鼠的研究阐明了K-ATP通道在胰腺内分泌功能中的各种作用：1）K-ATP通道是胰腺β细胞的静息膜电位的主要决定因素，2）葡萄糖和磺酰脲诱导的β细胞的膜去极化都需要K-ATP通道的关闭，3）葡萄糖和磺酰脲诱导的β细胞内钙浓度升高都需要关闭K-ATP通道，4）葡萄糖和磺酰脲诱导的胰岛素分泌主要由K-ATP通道依赖性途径介导，5）K-ATP通道对于胰岛的β细胞存活和结构是重要的，6）K-ATP通道在胰岛细胞的分化中是重要的，和7）葡萄糖应答细胞中的K-ATP通道通常参与葡萄糖感知与细胞兴奋性的偶联。有趣的是，尽管在葡萄糖诱导的胰岛素分泌中存在严重缺陷，Kir6.2敲除小鼠在葡萄糖耐量方面仅显示出非常轻微的损害。然而，当敲除小鼠随着年龄增长而变得肥胖时，它们会出现空腹高血糖和葡萄糖耐受不良，而在没有肥胖的老年敲除小鼠中，空腹高血糖和葡萄糖耐受不良都不明显，这表明葡萄糖诱导的胰岛素分泌的遗传缺陷和由于环境因素导致的获得性胰岛素抵抗都是Kir6.2敲除小鼠发生糖尿病所必需的。因此，Kir6.2G132S Tg小鼠和Kir6.2敲除小鼠提供了2型糖尿病模型，并阐明了K-ATP通道在胰腺内分泌功能中的各种作用。
The regulation of insulin secretion from pancreatic beta-cells depends critically on the activities of their plasma membrane ion channels. ATP-sensitive K+ channels (K-ATP channels) are present in many cells and regulate a variety of cellular functions by coupling cell metabolism with membrane potential. The activity of the K-ATP channels in pancreatic beta-cells is regulated by changes in the ATP and ADP concentrations (ATP/ADP ratio) caused by glucose metabolism. Thus, the K-ATP channels are the ATP and ADP sensors in the regulation of glucose-induced insulin secretion. K-ATP channels are also the target of sulfonylureas, which are widely used in the treatment of type 2 diabetes. Molecular cloning of the two subunits of the pancreatic beta-cell K-ATP channel, Kir6.2 (an inward rectifier K+ channel member) and SUR1 (a receptor for sulfonylureas), has provided great insight into its structure and function. Kir6.2 subunits form the K+ ion-permeable pore and primarily confer inhibition of the channels by ATP, while SUR1 subunits confer activation of the channels by MgADP and K+ channel openers, such as diazoxide, as well as inhibition by sulfonylureas. The SUR1 subunits also enhance the sensitivity of the channels to ATP, To determine the physiological roles of K-ATP channels directly, we have generated two kinds of genetically engineered mice: mice expressing a dominant-negative form of Kir6.2 specifically in the pancreatic beta-cells (Kir6.2G132S Tg mice) and mice lacking Kir6.2 (Kir6.2 knockout mice). Studies of these mice elucidated various roles of the K-ATP channels in endocrine pancreatic function: 1) the K-ATP channels are the major determinant of the resting membrane potential of pancreatic beta-cells, 2) both glucose- and sulfonylurea-induced membrane depolarization of beta-cells require closure of the K-ATP channels, 3) both glucose- and sulfonylurea-induced rises in intracellular calcium concentration in beta-cells require closure of the K-ATP channels, 4) both glucose- and sulfonylurea-induced insulin secretions are mediated principally by the K-ATP channel-dependent pathway, 5) the K-ATP channels are important for beta-cell survival and architecture of the islets, 6) the K-ATP channels are important in the differentiation of islet cells, and 7) the K-ATP channels in glucose-responsive cells generally participate in coupling glucose sensing with cell excitability, interestingly, despite the severe defect in glucose-induced insulin secretion, Kir6.2 knockout mice show only a very mild impairment in glucose tolerance. However, when the knockout mice become obese with age, they develop fasting hyperglycemia and glucose intolerance, while neither fasting hyperglycemia nor glucose intolerance is evident in the aged knockout mice without obesity, suggesting that both the genetic defect in glucose-induced insulin secretion and the acquired insulin resistance due to environmental factors are necessary to develop diabetes in Kir6.2 knockout mice. Thus, Kir6.2G132S Tg mice and Kir6.2 knockout mice provide a model of type 2 diabetes and clarify the various roles of K-ATP channels in endocrine pancreatic function.