Dynamics of Oxygen Supply Regulation in the Microvasculature

人体每个器官的微血管系统不断地调节氧气(O2)向这些器官中的每个细胞的输送。该项目的目标是了解微血管系统如何调节氧气供应，从而使毛细血管获得足够的氧气供应附近的组织。我们有证据表明，将氧气输送到组织的红细胞(RBC)也负责向形成毛细血管壁的内皮细胞发送信号，表明每个红细胞携带了多少氧气。然后，内皮细胞将电信号从毛细血管传导到控制血流量的小动脉，根据红细胞中的O2水平是否发生变化来增加或减少血流量。如果红细胞中的氧气水平降低，就会向上游传递一个信号，以扩张小动脉，增加血流量。红细胞释放的信号分子是三磷酸腺苷(ATP)。这项建议集中在两个问题上。我们的第一个目标是确定红细胞对O2水平的变化能以多快的速度释放ATP。我们的第二个目标是确定活组织中的微血管系统对毛细血管中O2水平变化的反应速度。ATP释放的速度决定了红细胞向毛细血管报告其氧气水平的准确性。为了测量释放时间，我们建造了“微流控”装置(带有模拟微血管的通道的小室)，这些装置具有小的氧气渗透窗口，使我们能够快速改变流经通道的红细胞的氧气水平。我们建议通过使用非常灵敏的摄像机检测当ATP与萤火虫提取物反应时产生的光来测量从O2水平变化到ATP释放的延迟。微血管系统对氧气变化的反应有多快，将提供有关调节系统各个方面的信息，并确认毛细血管是否可以调节微动脉血流。使用与肌肉接触的类似微流控装置改变大鼠或小鼠肌肉组织中的氧气水平，并使用显微镜和高分辨率摄像机对微血管反应进行成像。我们的第三个目标是确定用于氧气控制的肌肉组织的目标体积。100年前报道的、至今仍在使用的第一个氧气调节模型提出，每个毛细血管周围有一个圆柱体组织作为目标体积。基于我们在过去五年中对肌肉纤维周围毛细血管网络结构的研究，我们提出目标体积是骨骼肌束，即包裹在结缔组织层中的一束肌肉纤维。最小的小动脉和小静脉穿透结缔组织，提供覆盖整个肌束(和肌肉)的毛细血管网络。从这个项目中获得的知识将为自然界中最基本的监管系统之一提供新的见解，并将对理解广泛的心血管疾病产生深远的影响。

The microvasculature of every organ of the body is constantly regulating the delivery of oxygen (O2) to every cell in these organs. The goal of this project is to understand how the microvasculature regulates O2 supply such that the capillaries receive enough O2 to supply the nearby tissue. We have evidence that the red blood cell (RBC) which carries O2 to tissue is also responsible for signaling the endothelial cells that form the capillary wall how much O2 each RBC is carrying. The endothelial cells then conduct an electrical signal from the capillaries to the arterioles that control blood flow to either increase or decrease flow depending on whether the O2 levels in the RBCs are changing. If the O2 level in the RBC decreases a signal is conducted upstream to dilate arterioles and increase blood flow. The signaling molecule that the RBCs release is adenosine triphosphate (ATP). This proposal focuses on two questions. Our first goal is to determine how rapidly ATP can be released from the RBC in response to a change in O2 levels. Our second goal is to determine how rapidly the microvasculature in a living tissue can respond to a change in O2 levels in capillaries. How fast ATP can be released determines how accurately the RBC can report its O2 levels to the capillary. To measure release times we have built "microfluidic" devices (chambers with channels mimicking microvessels) that have small O2 permeable windows which allow us to rapidly change O2 levels of RBCs flowing through the channels. We propose to measure the delay from the change in O2 levels to when ATP is released by detect the light produced when ATP reacts with firefly extract using a very sensitive video camera. How rapidly the microvasculature responds to a change in O2 will give information on all aspects of the regulatory system and confirm whether capillaries can regulate arteriolar blood flow. O2 levels in muscle tissue in rats or mice are changed using a similar microfluidic device in contact with the muscle and the microvascular response is imaged using a microscope and high resolution video cameras. Our third goal is to determine the target volume of muscle tissue for O2 control. The first model of O2 regulation reported 100 years ago and still used today proposed a cylinder of tissue around each capillary as the target volume. Based on our research over the past five years examining the structure of the capillary network around muscle fibres we propose that the target volume is the skeletal muscle fascicle, a bundle of muscle fibres enclosed in a connective tissue layer. The smallest arterioles and venules penetrate the connective tissue and supply a network of capillaries that extend the entire length of the fascicle (and muscle). The knowledge gained from this project will provide new insights into one of the most fundamental regulatory systems in nature and will have far reaching implications in understanding a wide range of cardiovascular diseases.