Vascular KATP Channel Modulation in Hypercapnic Acidosis

描述（由申请人提供）：ATP敏感性K+通道（KATP）将中间代谢与细胞兴奋性偶联，并在反应性充血中发挥重要作用。充血是缺血预处理的心脏保护作用和脑循环活动依赖性自动调节的基础，并涉及O2、CO2和pH的感受。我们最近的研究表明，KATP通道确实在高CO2/低pH下被激活。质子对KATP的调节是重要的，因为pH值的下降通常伴随着各种代谢应激，并且比单独的能量消耗更常见。这种调节可以使细胞改变其膜的兴奋性，以响应各种各样的生理和病理生理条件。然而，以前的研究的pH敏感性是相当有争议的：质子被证明是刺激细胞内源性KATP在一些研究，但抑制它在其他人。ATP、ADP和Mg ++对通道活性的间接作用使这种不一致进一步复杂化。因此，尚不清楚KATP在高碳酸血症和酸中毒期间是如何调节的，这些通道是否具有固有的pH敏感性，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和PCO 2和pH的精细操纵进行精细解剖。因此，在过去的3年中，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。为了进一步观察这些结果，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，2）证明通道蛋白中的传感机制，3）调节pH敏感性的决定因素及其与质子的相互作用，以及4）鉴定血管平滑肌中pH敏感的KATP亚型。这些信息不仅对心血管生理学有深远的影响，而且通过操纵pH传感机制来控制中风、癫痫和冠心病的细胞活性，对治疗方式的设计也有深远的影响。

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.