Cross-interactions between CO and NO signaling in microvascular endothelium

一氧化碳（CO）是由内源性血红素加氧酶（HO）合成的，它将血红素降解为胆绿素- ix α。像一氧化氮（NO）一样，一氧化碳在肝脏中具有血管扩张特性，内源性NO的产生似乎很低。然而，在产生相对较高NO的大脑中，这些气态氧化物如何相互作用以控制脑血管张力尚不清楚。本研究表明，来自HO的CO可作为一种强直调节剂，抑制成年大鼠脑中no依赖性血管舒张。我们发现，抑制内源性CO导致小动脉直径增加，并伴随着局部NO生成的增加。我们进一步研究了CO对NO生成的这种抑制功能是否通过CO结合产气酶的假血红素的能力来介导。利用培养的猪主动脉内皮细胞（PAECs），用NO特异性荧光染料测定NO的生成。co释放分子处理可减弱一氧化氮生成的时间依赖性升高。CO抑制NO生成的作用通过将paec暴露在白光下被抵消，这增加了CO直接针对NOS3的亚铁血红素抑制催化活性的可能性。此外，大鼠脑的免疫组织化学分析显示，HO-2发生在NOS1所在的神经元和蛛网膜小梁细胞中，也发生在表达NOS3的血管内皮中，这表明co和no的生成位点存在共定位。我们的研究结果表明，产气酶及其接收系统之间的空间关系在评估两种气体的作用方面具有重要意义。

Carbon monoxide (CO) is synthesized endogenously by heme oxygenase (HO) which degrades heme to biliverdin-IXα. Like nitric oxide (NO), CO has a vasodilatory property in the liver where endogenous NO production appears low. However, in the brain producing relatively high NO, how these gaseous monoxides interact each other to control cerebrovascular tone is unknown. Here we show that CO derived from HO acts as a tonic regulator against NO-dependent vasodilatation in the adult rat brain. We found that suppressing endogenous CO caused an increase in arteriolar diameter that was accompanied by an increase in local NO generation. We examined further if such an inhibitory function of CO on NO generation is mediated through the ability of CO to bind the prosthetic heme of gas-producing enzymes. Using cultured porcine aortic endothelial cells (PAECs), we measured NO generation by an NO-specific fluorescent dye. Treatment with CO-releasing molecule attenuated the time-dependent elevation of NO generation. This effect of CO to suppress NO generation was cancelled by exposing PAECs to white light raising a possibility that CO directly targets The ferrous heme of NOS3 to inhibit the catalytic activity. Furthermore, immunohistochemical analyses of the rat brain showed that HO-2 occurred in neurons and arachnoid trabecullar cells where NOS1 resided, and also in vascular endothelium expressing NOS3, suggesting colocalization of CO-and NO-generating sites. Our results demonstrate an importance of spatial relationship among the gas-producing enzymes and their reception systems in evaluating roles of the two gases.