Molecular mechanism and ultrastructure of the arterial chemoreceptor organ in chronically hypoxia

慢性缺氧（380 ℃，12周）大鼠颈动脉体增大，颈动脉体是感受动脉血中氧分压的主要器官。我们注意到一些慢性缺氧的超微结构特征，这些特征是两栖动物颈动脉迷路球细胞的特征：1）球细胞覆盖不完全，支持细胞大面积缺失，2）血管间质中长而薄的胞质突起，3）球细胞与内皮细胞、周细胞等紧密贴壁。使用超高压电子显微镜（400kV）和半薄切片的组合的三维分析清楚地表明，血管球细胞的不完全覆盖是基于血管球细胞和支持细胞之间的肥大程度的差异。由于两栖类动物动脉PO_2普遍较低，这些超微结构的相似性可能是缺氧适应的一般特征，它们都促进了从血液中摄取氧和释放儿茶酚胺到血液中。当比较常氧和慢性缺氧的颈动脉体和气管中肽能纤维的分布和丰度时，发现某些肽能免疫反应纤维的数量存在差异（SP、CGRP、VIP和其他）。这些免疫反应性纤维的增加表明，改变气道反射可能是缺氧适应的一个特点。为了阐明缺氧适应的生理机制，我们现在正在研究细胞内第二信使，如环腺苷酸和其他，在轴浆运输的神经纤维在慢性缺氧颈动脉体的不固定部分的影响。

The carotid bodies, which are the primary organs for sensing O_2 tension in arterial blood, are enlarged in rat exposed to chronic hypoxia (380 torr, 12 weeks). We noted some ultrastructural features with chronic hypoxia which are characteristic of the amphibian carotid labyrinth glomus cells : 1) incomplete covering of glomus cells with the supporting cell missing over a wide area, 2) long thin cytoplasmic projections in the intervascular stroma, and 3) intimate apposition of the glomus cells and endothelial cells, pericytes, and others. Threedimensional analysis using a combination of an ultra high voltage electron microscope (400kV) and semi-thin sections clearly demonstrated that the incomplete covering of glomus cells is based on a difference in an extent of hypertrophy between glomus cells and supporting cells. Because arterial PO_2 is generally low in amphibia, these ultrastructural similarities may be general features of hypoxic adaptation and facilitate both uptake of oxygen from blood and release of catecholamine into the blood.When the distribution and abundance of the peptidergic fibers were compared between normoxic and chronically hypoxic carotid bodies and tracheas, there was a difference in number of some peptide-immunoreactive fibers (SP,CGRP,VIP,and others). The increase of these immunoreactive fibers suggests that altered airway reflexes may be a feature of hypoxic adaptation. To clarify a physiological mechanism in the hypoxic adaptation, we are now studying an effect of intracellular second messengers, such as cyclic AMP and others, in axoplasmic transport of nerve fibers in unfixed sections of chronically hypoxic carotid body.