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，红细胞可以作为“传感器”，在氧气需求和输送不匹配时释放ATP，这种ATP可以通过与内皮上的嘌呤能（P2y）受体结合而引起血管舒张并改善局部血流量。除了直接的血管扩张作用，我们最近证明ATP也能够抑制交感血管收缩（“交感神经溶解”），这可以进一步帮助血液流动和氧气分配。我们的初步数据表明，前臂血管舒张剂对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血管舒张前列腺素。因此，本探索性研究计划的总体目标是直接验证内皮依赖性ATP介导的血管舒张是由于人类血管平滑肌细胞超极化的假设，并进一步验证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)我们将确定是否通过单独和联合抑制向内整流钾通道（KIR，通过氯化钡）和Na+/K+ ATP酶活性（通过多巴胺）来降低前臂血管扩张剂对局部动脉内给药ATP的反应；(2)我们将确定在抑制KIR通道和Na+/K+ atp酶活性后，人类前臂血管舒张剂对分级节律性握力运动的反应和肌肉收缩减弱交感1-肾上腺素能受体介导的血管收缩的能力是否受损。为实现这些目标所采用的方法是最先进的，包括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类前臂动脉和静脉血浆ATP浓度。这些研究的发现将为循环ATP引起局部血管舒张的机制以及引发超极化的假设信号通路是否参与骨骼肌收缩的血管控制提供独特的见解。鉴于内皮依赖性血管舒张受损是高危患者或已经表现出心血管疾病的患者的标志，并且某些患者（如糖尿病患者）红细胞中ATP释放受损，我们关于ATP介导的血管舒张机制的研究结果可能对理解生理（如运动、缺氧）和病理生理(如：老年健康和患病人群的冠状动脉和脑血管缺血状况。

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.