Lawrenson J G, Reid A R, Allt G
Reta Lila Weston Institute of Neurological Studies, Windeyer Building, University College London Medical School, Cleveland Street, London, W1P 6DB, UK.
Cell Tissue Res. 1997 May;288(2):259-65. doi: 10.1007/s004410050811.
Pial microvessels have commonly been used in studies of the blood-brain barrier because of their relative accessibility. To determine the validity of using the pial microvessel as a model system for the blood-brain barrier, we have extended the comparison of pial and cerebral microvessels at the molecular level by a partial characterization of the glycocalyx of pial endothelial cells, in view of the functional importance of anionic sites within the glycocalyx. Rat optic nerves were fixed by vascular perfusion. Anionic sites on the endothelium were labelled with cationic colloidal gold by means of post- and pre-embedding techniques. The effects of digestion of ultrathin sections on subsequent gold labelling was quantified following their treatment with a battery of enzymes. Biotinylated lectins, viz. wheat germ agglutinin and concanavalin A with streptavidin gold, were employed to identify specific saccharide residues. The results demonstrate that the luminal glycocalyx of pial microvessels is rich in sialic-acid-containing glycoproteins. Neuraminidase, which is specific for N-acetylneuraminic (sialic) acid, and papain (a protease with a wide specificity) significantly reduce cationic colloidal gold binding to the luminal endothelial cell plasma membrane. Wheat germ agglutinin (with an affinity for sialic acid) binds more to the luminal than abluminal plasma membrane, whereas concanavalin A, which binds mannose, binds more to the abluminal surface. Similar results have been obtained for cerebral cortical endothelial cells. With respect to these molecular characteristics, therefore, the pial and cortical microvessels appear to be the same. However, since the two vessel types differ in other respects, caution is urged regarding the use of pial microvessels to investigate the blood-brain barrier.
软脑膜微血管因其相对易于获取，常用于血脑屏障的研究。为了确定将软脑膜微血管用作血脑屏障模型系统的有效性，鉴于糖萼内阴离子位点的功能重要性，我们通过对软脑膜内皮细胞糖萼进行部分表征，在分子水平上扩展了软脑膜微血管与脑微血管的比较。大鼠视神经通过血管灌注固定。采用包埋后和包埋前技术，用阳离子胶体金标记内皮细胞上的阴离子位点。在用一系列酶处理超薄切片后，对其消化对后续金标记的影响进行了量化。使用生物素化凝集素，即麦胚凝集素和伴刀豆球蛋白A与链霉抗生物素蛋白金，来识别特定的糖残基。结果表明，软脑膜微血管的管腔糖萼富含含唾液酸的糖蛋白。对N - 乙酰神经氨酸（唾液酸）具有特异性的神经氨酸酶和木瓜蛋白酶（一种具有广泛特异性的蛋白酶）显著降低阳离子胶体金与管腔内内皮细胞质膜的结合。麦胚凝集素（对唾液酸有亲和力）与管腔质膜的结合多于与管腔外质膜的结合，而结合甘露糖的伴刀豆球蛋白A与管腔外表面的结合更多。脑皮质内皮细胞也得到了类似的结果。因此，就这些分子特征而言，软脑膜微血管和皮质微血管似乎是相同的。然而，由于这两种血管类型在其他方面存在差异，在使用软脑膜微血管研究血脑屏障时应谨慎。
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