Role of circulating ATP and smooth muscle cell hyperpolarization in vascular cont

描述(申请人提供)：血流和氧气输送与组织需氧量的匹配是最基本的生理过程之一。最近的证据表明，红细胞可以作为“传感器”，在氧需求和供氧量不匹配的情况下释放ATP，这种ATP可以通过与内皮上的嘌呤能(P2y)受体结合，在这种情况下引起血管扩张，改善局部血流量。除了直接的血管扩张作用外，我们最近还证明了ATP还能够抑制交感神经血管收缩(交感神经溶解)，这可以进一步帮助血流和氧气分配。我们的初步数据表明，前臂血管扩张对ATP的反应不是由于腺苷的分解，重要的是，它独立于一氧化氮和扩张血管的前列腺素。因此，这一探索性研究计划的总体目标是直接验证内皮依赖的ATP介导的血管扩张是由于人类血管平滑肌细胞超极化的假设，并进一步测试所提出的通路是否参与收缩肌肉的血管控制。为了验证我们的假设，我们将解决以下具体目标：(1)我们将确定对局部动脉内给药的ATP的前臂血管扩张剂反应是否因单独和联合抑制内向整流钾通道(KIR；通过氯化钡)和Na+/K+ATPase活性(通过欧拜因)而降低；以及(2)我们将确定在抑制KIR通道和Na+/K+ATPase活性后，前臂对分级有节奏的握手运动的血管扩张剂反应以及肌肉收缩钝化交感1-肾上腺素能受体介导的血管收缩的能力是否受损。用于解决这些目标的方法是最先进的，涉及在休息和运动期间局部(动脉内)给药各种研究药物，以及测量年轻健康人的前臂动脉和静脉血浆ATP浓度。这项研究的发现将为了解循环中的三磷酸腺苷引起局部血管扩张的机制，以及引发超极化的假想信号通路是否参与收缩骨骼肌的血管控制提供独特的见解。鉴于内皮依赖性血管扩张受损是心血管疾病高危患者或已经出现心血管疾病的患者的标志，并且某些患者(例如糖尿病患者)的红细胞ATP释放受到损害，我们关于ATP介导的血管扩张潜在机制的研究结果对于了解老年健康和疾病患者在生理(例如运动、缺氧)和病理生理(例如冠状动脉和脑血管缺血)条件下局部血管控制受损具有重要意义。 公共卫生相关性：本申请中概述的研究旨在解决有关血液流动和氧气输送如何控制到人类外周组织的基本问题。了解这些基本的调节机制将提供重要的信息，可能会激发人们对如何改善急性和慢性心血管并发症风险人群的区域血流和氧气输送的想法。

DESCRIPTION (provided by applicant): The matching of blood flow and oxygen delivery to tissue oxygen demand is one of the most fundamental physiological processes. Recent evidence indicates that the red blood cell can act as a "sensor" and releases ATP during mismatches in oxygen demand and delivery, and this ATP can evoke vasodilation and improve local blood flow under such conditions via binding to purinergic (P2y) receptors on the endothelium. In addition to the direct vasodilatory effect, we have recently demonstrated that ATP is also capable of inhibiting sympathetic vasoconstriction ("sympatholytic"), which could further aid in blood flow and oxygen distribution. Our preliminary data indicates that the forearm vasodilator responses to ATP are not due to breakdown to adenosine, and importantly, are independent of nitric oxide and vasodilating prostaglandins. Thus, the overall goal of this exploratory research program is to directly test the hypothesis that endothelium-dependent ATP- mediated vasodilation is due to vascular smooth muscle cell hyperpolarization in humans, and to further test whether the proposed pathways are involved in vascular control in contracting muscle. To test our hypotheses we will address the following specific aims: (1) we will determine whether the forearm vasodilator responses to local intra-arterial administration of ATP are reduced by individual and combined inhibition of inward rectifying potassium channels (KIR; via barium chloride) and Na+/K+ ATPase activity (via oubain); and (2) we will determine whether the forearm vasodilator responses to graded rhythmic handgrip exercise and the ability of muscle contractions to blunt sympathetic 1-adrenergic receptor mediated vasoconstriction are impaired after inhibition of KIR channels and Na+/K+ ATPase activity in humans. The methods employed to address these aims are state-of-the-art and involve local (intra-arterial) administration of various study drugs at rest and during exercise, and measurements of forearm arterial and venous plasma ATP concentrations in young healthy humans. The findings from the proposed studies should provide unique insight into the mechanisms by which circulating ATP causes local vasodilation, and whether the hypothesized signaling pathways evoking hyperpolarization are involved in vascular control in contracting skeletal muscle. Given that impaired endothelium-dependent vasodilation is a hallmark of patients at risk or whom already exhibit cardiovascular disease, and that ATP release from red blood cells of certain patients (e.g. diabetics) is impaired, our findings regarding the mechanisms underlying ATP-mediated vasodilation could have significant implications for understanding impaired local vascular control during physiological (e.g., exercise, hypoxia) and pathophysiological (e.g., coronary and cerebrovascular ischemia) conditions in older healthy and diseased humans. PUBLIC HEALTH RELEVANCE: The studies outlined in this application are designed to address fundamental questions regarding how blood flow and oxygen delivery are controlled to peripheral tissues in humans. Understanding these basic regulatory mechanisms will provide important information that may stimulate ideas on how to improve regional blood flow and oxygen delivery in patient populations at risk for both acute and chronic cardiovascular complications.