Martínez-Palomo A, Erlij D
Proc Natl Acad Sci U S A. 1975 Nov;72(11):4487-91. doi: 10.1073/pnas.72.11.4487.
Freeze-fracture studies have shown a network of intramembrane fibrils in the tight junctions of epithelia. A direct correlation between the number of fibrils and junctional permeability has been suggested by previous studies. However, we have made two groups of observations showing that junctional permeability is not univocally related to the complexity of the network revealed by freeze-fracture. (i) The tight junctions of the rabbit ileum mucosa are permeable to lanthanum, although they have a complex network of fibrils resembling the junctions of toad urinary bladder, which are impermeable to lanthanum. (ii) The tight junctions of the toad urinary bladder are normally of low permeability; however, when the luminal solution is made hypertonic with lysine, junctional permeability markedly increases and lanthanum permeates through the tight junctions. In freeze-fracture replicas, no differences between the fibrils of control and lysine-treated bladders were found. Our results indicate that junctional permeability is controlled not only by the complexity of the fibrilar network, but that some features of the junctions or the fibrils themselves, not yet revealed by electron microscopy, play a central role in regulating epithelial permeability.
冰冻蚀刻研究表明，上皮细胞紧密连接处存在膜内纤维网络。先前的研究表明纤维数量与连接通透性之间存在直接关联。然而，我们进行了两组观察，结果显示连接通透性与冰冻蚀刻所揭示的网络复杂性并非唯一相关。（i）兔回肠黏膜的紧密连接对镧具有通透性，尽管它们具有类似于蟾蜍膀胱连接处的复杂纤维网络，而蟾蜍膀胱连接处对镧是不通透的。（ii）蟾蜍膀胱的紧密连接通常通透性较低；然而，当管腔溶液用赖氨酸使其变为高渗时，连接通透性显著增加，镧可透过紧密连接。在冰冻蚀刻复制品中，未发现对照膀胱和经赖氨酸处理的膀胱的纤维之间存在差异。我们的结果表明，连接通透性不仅受纤维网络复杂性的控制，而且连接处或纤维本身的一些尚未被电子显微镜揭示的特征在调节上皮通透性方面起着核心作用。
