Cross-interactions between CO and NO signaling in microvascular endothelium

一氧化碳（CO）是由血红素加氧酶（HO）内源性合成的，HO将血红素降解为胆绿素-IX α。与一氧化氮（NO）一样，CO在肝脏中具有血管舒张特性，其中内源性NO产生似乎较低。然而，在产生相对高的NO的大脑中，这些气态一氧化物如何相互作用以控制脑血管紧张度尚不清楚。在这里，我们表明，CO来自HO作为一个紧张性调节剂对NO依赖性血管舒张在成年大鼠大脑。我们发现抑制内源性CO会导致小动脉直径增加，并伴有局部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是通过CO结合产气酶的血红素的能力来介导的。使用培养的猪主动脉内皮细胞（PAECs），我们测量NO产生的NO特异性荧光染料。用CO释放分子处理减弱了NO产生的时间依赖性升高。CO抑制NO生成的这种作用通过将PAECs暴露于白色光而被取消，这提高了CO直接靶向NOS 3的亚铁血红素以抑制催化活性的可能性。此外，免疫组织化学分析表明，HO-2发生在神经元和蛛网膜小梁细胞的NOS 1居住，也在血管内皮细胞表达NOS 3，这表明CO和NO产生的网站共定位。我们的研究结果表明，在评估两种气体的作用的气体产生的酶和它们的接收系统之间的空间关系的重要性。

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.