Department of Physics, Wake Forest University, Winston-Salem, North Carolina 27109, USA.
J Biol Chem. 2011 Sep 23;286(38):33567-79. doi: 10.1074/jbc.M111.228650. Epub 2011 Jul 30.
Nitric oxide (NO) acts as a smooth muscle relaxation factor and plays a crucial role in maintaining vascular homeostasis. NO is scavenged rapidly by hemoglobin (Hb). However, under normal physiological conditions, the encapsulation of Hb inside red blood cells (RBCs) significantly retards NO scavenging, permitting NO to reach the smooth muscle. The rate-limiting factors (diffusion of NO to the RBC surface, through the RBC membrane or inside of the RBC) responsible for this retardation have been the subject of much debate. Knowing the relative contribution of each of these factors is important for several reasons including optimization of the development of blood substitutes where Hb is contained within phospholipid vesicles. We have thus performed experiments of NO uptake by erythrocytes and microparticles derived from erythrocytes and conducted simulations of these data as well as that of others. We have included extracellular diffusion (that is, diffusion of the NO to the membrane) and membrane permeability, in addition to intracellular diffusion of NO, in our computational models. We find that all these mechanisms may modulate NO uptake by membrane-encapsulated Hb and that extracellular diffusion is the main rate-limiting factor for phospholipid vesicles and erythrocytes. In the case of red cell microparticles, we find a major role for membrane permeability. These results are consistent with prior studies indicating that extracellular diffusion of several gas ligands is also rate-limiting for erythrocytes, with some contribution of a low membrane permeability.
一氧化氮（NO）作为平滑肌松弛因子，在维持血管内环境稳态中起着至关重要的作用。NO 可被血红蛋白（Hb）迅速清除。然而，在正常生理条件下，Hb 被包裹在红细胞（RBC）内会显著减缓 NO 的清除速度，从而使 NO 能够到达平滑肌。导致这种减缓的限速因素（NO 扩散到 RBC 表面、穿过 RBC 膜或进入 RBC 内部）一直是争论的焦点。了解这些因素中的每一个的相对贡献对于几个原因很重要，包括血红蛋白包含在磷脂囊泡内的血液替代品的开发的优化。因此，我们进行了红细胞和红细胞衍生的微粒体摄取 NO 的实验，并对这些数据以及其他数据进行了模拟。我们的计算模型除了包含细胞内 NO 扩散外，还包含细胞外扩散（即 NO 扩散到膜上）和膜通透性。我们发现，所有这些机制都可能调节膜包裹 Hb 对 NO 的摄取，并且细胞外扩散是磷脂囊泡和红细胞摄取 NO 的主要限速因素。对于红细胞微粒体，我们发现膜通透性起着主要作用。这些结果与先前的研究一致，表明几种气体配体的细胞外扩散也是红细胞摄取的限速因素，同时还存在一定程度的低膜通透性。
