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

描述（由申请人提供）：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，红细胞可以充当“传感器”，并在氧需求和输送不匹配期间释放ATP，并且这种ATP可以通过结合内皮上的嘌呤能（P2 γ）受体引起血管舒张并在这种条件下改善局部血流。除了直接的血管舒张作用，我们最近已经证明ATP也能够抑制交感神经血管收缩（“交感神经阻滞”），这可以进一步帮助血液流动和氧气分布。我们的初步数据表明，前臂血管扩张反应ATP不是由于分解为腺苷，重要的是，是独立的一氧化氮和血管扩张的肾上腺素。因此，该探索性研究计划的总体目标是直接检验内皮依赖性ATP介导的血管舒张是由于人体血管平滑肌细胞超极化所致的假设，并进一步检验所提出的途径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）我们将确定是否前臂血管扩张反应的局部动脉内给药的ATP是减少由个别和联合抑制内向整流钾通道（KIR;通过氯化钡）和Na+/K+ ATP酶活性（via browser）;以及（2）我们将确定前臂血管舒张对分级节律性握力运动的反应以及肌肉收缩钝化交感神经1-肾上腺素能受体介导的血管收缩在抑制人的KIR通道和Na+/K+ ATP酶活性后受损。用于实现这些目标的方法是最先进的，包括在静息和运动期间局部（动脉内）给予各种研究药物，以及测量年轻健康人的前臂动脉和静脉血浆ATP浓度。从拟议的研究结果应该提供独特的见解循环ATP引起局部血管舒张的机制，以及是否假设的信号通路引起超极化参与血管控制收缩骨骼肌。鉴于内皮依赖性血管舒张受损是处于危险中或已经表现出心血管疾病的患者的标志，并且某些患者（例如糖尿病患者）的红细胞的ATP释放受损，我们关于ATP介导的血管舒张的潜在机制的发现可能对理解生理（例如，运动，缺氧）和病理生理学（例如，冠状动脉和脑血管局部缺血）状况。 公共卫生相关性：本申请中概述的研究旨在解决有关如何控制血流和氧气输送到人体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，可能会激发关于如何改善急性和慢性心血管并发症风险患者群体的局部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.