Hicks R M
J Cell Biol. 1966 Jan;28(1):21-31. doi: 10.1083/jcb.28.1.21.
Permeability barriers must exist in transitional epithelium to prevent the free flow of water from underlying blood capillaries through the epithelium into the hypertonic urine, and such a barrier has now been demonstrated in isolated bladders. This barrier is passive in function and can be destroyed by damaging the luminal surface of the transitional epithelium with sodium hydroxide and 8 M urea solutions, by digesting it with trypsin, lecithinase C, and lecithinase D, or by treating it with lipid solvents such as Triton x 100 and saponin. From this it is concluded that the barrier depends on the integrity of lipoprotein cell membranes. The barrier function is also destroyed by sodium thioglycollate solutions, and electron microscope investigations show that sodium thioglycollate damages the thick asymmetric membrane which limits the luminal face of the superficial squamous cell. Cytochemical staining shows the epithelium to contain disulfide and thiol groups and to have a concentration of these groups at the luminal margin of the superficial cells. It thus appears that the permeability barrier also depends on the presence of disulfide bridges in the epithelium, and it is presumed that these links are located in keratin. Because of the effect of thioglycollates, both on the barrier function and on the morphology of the membrane, it is suggested that keratin may be incorporated in the thick barrier membrane. It is proposed that the cells lining the urinary bladder and ureters should be regarded as a keratinizing epitheluim.
移行上皮中必定存在渗透屏障，以防止水从下层的毛细血管自由穿过上皮细胞流入高渗尿液中，现已在离体膀胱中证实了这种屏障的存在。这种屏障在功能上是被动的，可用氢氧化钠和8M尿素溶液破坏移行上皮的腔面、用胰蛋白酶、卵磷脂酶C和卵磷脂酶D消化、或用Triton x 100和皂苷等脂质溶剂处理来破坏它。由此得出结论，该屏障依赖于脂蛋白细胞膜的完整性。巯基乙酸钠溶液也会破坏屏障功能，电子显微镜研究表明，巯基乙酸钠会损伤限制表层鳞状细胞腔面的厚不对称膜。细胞化学染色显示上皮细胞含有二硫键和巯基，且这些基团在表层细胞的腔缘处浓度较高。因此，似乎渗透屏障也依赖于上皮中存在二硫键桥，据推测这些连接位于角蛋白中。由于巯基乙酸盐对屏障功能和膜形态都有影响，提示角蛋白可能整合于厚的屏障膜中。有人提出，膀胱和输尿管内衬的细胞应被视为一种角化上皮。
