de Wit Cor, Wölfle Stephanie E
Institut für Physiologie, Universität zu Lübeck, Germany.
Curr Pharm Biotechnol. 2007 Feb;8(1):11-25. doi: 10.2174/138920107779941462.
Arterioles within the microcirculation control organ blood flow and represent the main peripheral resistance within the circulation. However, larger vessels with a diameter of more than 150 microm are mostly used to study vascular behavior. Although arterioles have features in common with these conducting vessels, they exhibit distinct properties and the contribution of different pathways to constriction or relaxation varies with vessel size. This is especially the case for endothelium-dependent relaxations, which occur in response to mechanical stimuli (e.g. blood flow) and agonists. Autacoids released from the endothelium include nitric oxide, prostaglandins and an endothelium-derived hyperpolarizing factor (EDHF). Whereas nitric oxide is dominant in larger vessels, the importance of EDHF increases with decreasing vessel size. Its chemical nature is still a matter of debate and different substances have been identified to act as an EDHF in different vascular beds, e.g. epoxyeicosanoids, potassium ions, anandamide, hydrogen peroxide or C-type natriuretic peptide. Despite this heterogeneity of proposed factors it is unclear if such a factor indeed exists in all vessels since the hyperpolarization of vascular smooth muscle has been proposed to be induced by simple current transfer from the adjacent endothelium. For this to occur the cells need to be electrically coupled and this requirement is fulfilled by gap junctions which are composed of connexins forming intercellular channels. Aside from myoendothelial coupling gap junctions also interconnect endothelial cells thus creating a functional unit, which efficiently synchronizes cellular behavior within the arteriolar tree of the microcirculation.
微循环中的小动脉控制着器官的血流，是循环系统中主要的外周阻力。然而，直径超过150微米的较大血管大多用于研究血管行为。尽管小动脉与这些传导血管有共同特征，但它们表现出独特的特性，不同途径对收缩或舒张的贡献随血管大小而变化。内皮依赖性舒张尤其如此，它是对机械刺激（如血流）和激动剂的反应。内皮释放的自分泌物质包括一氧化氮、前列腺素和内皮衍生的超极化因子（EDHF）。在较大血管中一氧化氮起主导作用，而EDHF的重要性随着血管尺寸减小而增加。其化学性质仍存在争议，在不同血管床中已鉴定出不同物质可作为EDHF，例如环氧二十碳三烯酸、钾离子、花生四烯酸乙醇胺、过氧化氢或C型利钠肽。尽管所提出的因子存在这种异质性，但尚不清楚这种因子是否确实存在于所有血管中，因为有人提出血管平滑肌的超极化是由相邻内皮的简单电流传递诱导的。要发生这种情况，细胞需要电偶联，而由连接蛋白形成细胞间通道的缝隙连接满足了这一要求。除了肌内皮偶联外，缝隙连接还使内皮细胞相互连接，从而形成一个功能单元，有效地同步微循环小动脉树内的细胞行为。
