Vascular KATP Channel Modulation in Hypercapnic Acidosis

描述(申请人提供)：ATP敏感性钾通道(KATP)将中间代谢与细胞兴奋性结合起来，在反应性充血中发挥重要作用。众所周知，充血是缺血预适应的心脏保护作用和脑循环活动依赖的自动调节的基础，涉及对O2、CO2和pH的感知。我们最近的研究表明，KATP通道确实在高coz/低pH时被激活。质子对KATP的调节很重要，因为pH水平的下降经常伴随着各种代谢压力，而且比单一的能量耗尽更常见。这种调节可能使细胞能够改变它们的膜兴奋性，以响应各种各样的生理和病理生理条件。然而，以往关于pH敏感性的研究颇具争议：一些研究表明质子能刺激细胞内源性KATP，而另一些研究则抑制细胞内源性KATP。ATP、ADP和镁对通道活动的间接影响使这种不一致变得更加复杂。因此，目前还不清楚KATP在高碳酸血症和酸中毒过程中是如何调节的，这些通道是否天生对pH敏感，以及调节的分子机制是什么。克隆的KATP通道是解决这些问题的理想选择，它允许对表达系统中的调节机制进行精细的剖析，并对PCO2和pH进行精细的操作。因此，在过去的三年里，我们一直在研究克隆的KATP的pH敏感性。我们的初步数据清楚地表明，质子是KATP的有效激活剂。为了进一步研究这些结果，我们提出了以下研究：1)阐明高碳酸血症和酸中毒对KATP的调节作用；2)阐明通道蛋白的感觉机制；3)调节pH敏感性的决定因素及其与质子的相互作用；4)鉴定血管平滑肌中对pH敏感的KATP亚型。这些信息不仅应该对心血管生理学产生深远的影响，还应该通过操纵pH传感机制来控制中风、癫痫和冠心病的细胞活动，从而对治疗模式的设计产生深远的影响。

DESCRIPTION (provided by applicant): ATP-sensitive K+ channels (KATP) couple the intermediary metabolism to cellular excitability, and play an important role in reactive hyperemia. It is known that hyperemia underlies the cardio-protective effect of ischemic preconditioning and the activity-dependent auto-regulation of cerebral circulation, and involves sensing of O2, CO2 and pH. Our recent studies indicate that KATP channels are indeed activated with high COz / low pH. The regulation of KATP by protons is significant, because a drop in pH levels often accompanies various metabolic stresses and is more frequently seen than sole energy depletion. Such regulation may enable cells to change their membrane excitability in response to a wide variety of physiologic and pathophysiologic conditions. However, previous studies on the pH sensitivity were rather controversial: proton was shown to stimulate cell-endogenous KATP in some studies but inhibit it in others. The inconsistence is further complicated by the indirect effect of ATP, ADP and Mg ++ on channel activity. Thereby, it is unclear how the KATP is modulated during hypercapnia and acidosis, whether these channels are inherently pH-sensitive, and what the molecular mechanisms underlying the modulation are. The cloned KATP channels are ideal for addressing these questions, which allow a fine dissection of the modulatory mechanisms and elaborate manipulations of PCO2 and pH in the expression system. Thereby, we have been studying the pH sensitivity of the cloned KATP over the past 3 years. Our preliminary data have clearly shown that proton is a potent activator of the KATP. TO further these observations, we have proposed studies aimed at 1) elucidating the modulation of KATP by hypercapnia and acidosis, 2) demonstrating the sensing mechanisms in the channel proteins, 3) determining factors and their interactions with protons in regulating the pH sensitivity, and 4) identifying the pH-sensitive KATP isoforms in vascular smooth muscles. This information should have profound impacts not only on cardiovascular physiology but also on the design of therapeutical modalities by manipulating the pH-sensing mechanisms to control cellular activity in stroke, epilepsy and coronary heart disease.