Cytochemical Studies of Blood Retinal Barrier

为了研究血视网膜屏障的特性，用不同的过氧化物酶分子作为细胞化学示踪剂。我们在电子显微镜下观察了示踪剂穿透脉络膜毛细血管和视网膜色素上皮(RPE)细胞的基底部。有趣的是，带阴离子电荷的较小示踪剂的渗透速度并不比带阳离子电荷的较大示踪剂快得多。利用阳离子铁蛋白(CF)标记超薄冰冻切片，检测RPE细胞和脉络膜毛细血管内和细胞外阴离子部位的分布。我们证实了纤维颗粒沿RPE细胞和绒毛毛细血管的基底层分布。在RPE细胞连接中，除缝隙连接外，细胞连接表面均可见明显的CF颗粒。通过用不同的凝集素-铁蛋白标记超薄冰冻切片，我们发现这些阴离子中心主要是由于唾液酸。据报道，Bruch膜具有阴离子位置，可能作为电荷屏障，阻止阴离子分子从脉络膜毛细血管到RPE细胞和外部神经视网膜的移动。我们的研究结果表明，RPE细胞和Bruch膜的基底部均被阳离子铁蛋白标记，这表明不仅Bruch膜，而且色素上皮的基底层也具有阴离子位置，并起到电荷屏障的作用。

In order to study the characteristics of blood retinal barrier, various peroxidase molecules were utilized as cytochemical tracers. We observed the tracers penetrated through choriocapillaries and basal portion of Retinal Pigment Epithelial (RPE) cells under an electron microscope. Interestingly, smaller tracers with anionic charges did not penetrate much faster than larger tracers with cationic charges. The characteristics of invasion of such tracer proteins were modified according to their electrical charges.The extracellular and intracellular distribution of anionic sites in RPE cells and choriocapillaries were examined by labeling ultra-thin frozen sections with cationized ferritin (CF). We demonstrated CF particles were distributed along the basal laminae of RPE cells and choriocapillaries. In RPE cell junctions, CF particles were evident on the surfaces of cell junctions except gap junctions. By labeling ultra-thin frozen sections with various lectin-ferritin, we showed these anionic site were mainly due to sialic acids.Essner et al. have reported that Bruch's membrane has anionic sites and may serve as a charge barrier against the movement of anionic molecules from the choriocapillaries to RPE cells and the outer neural retina. Our findings showing that basal infoldings of RPE cells and the Bruch's membrane are denely labeled with cationized ferritin suggest that not only the Bruch's membrane but also the basal infoldings of the pigment epithelium have anionic sites and play a role as charge barrier.