Fluorescent membrane probes and the mechanism of maintenance of cellular asymmetry in epithelia.
Fluorescent membrane probes and the mechanism of maintenance of cellular asymmetry in epithelia.
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发表时间：
1982
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通讯作者：
P. Dragsten;J. Handler;R. Blumenthal
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作者：
P. Dragsten;J. Handler;R. Blumenthal
各个上皮细胞在形态、酶分布、脂质组成、离子渗透性以及顶（粘膜）膜与基底外侧（浆膜）膜上对药物和激素的敏感性方面是不对称的。有人认为，紧密连接形成顶端和基底外侧表面之间的形态边界，通过形成膜成分跨过这些膜的横向扩散的屏障，有助于维持这种细胞不对称性。我们通过用荧光探针选择性标记顶膜或基底膜并确定 1) 探针是否可以在膜中横向扩散，以及 2) 是否可以穿过紧密连接区域到达最初未标记的细胞一侧，直接测试了这一假设。我们的结果表明膜结合凝集素和一些脂质探针无法穿过紧密连接区域。凝集素在细胞表面不动，但脂质探针在膜中自由扩散。我们提出，脂质探针穿过紧密连接的能力与其翻转到细胞膜双层的内部单层的能力相关，并且紧密连接因此仅对外部单层中的脂质形成屏障。不同脂质探针的扩散速率的差异似乎也反映了内膜小叶与外膜小叶的不同物理特征。
Individual epithelial cells are asymmetric with respect to morphology, distribution of enzymes, lipid composition, ionic permeability, and sensitivity to drugs and hormones on the apical (mucosal) versus basolateral (serosal) membranes. It has been suggested that the tight junction, which forms the morphological boundary between apical and basolateral surfaces, helps to maintain this cellular asymmetry by forming a barrier to lateral diffusion of membrane constituents across these membranes. We have directly tested this hypothesis by selectively labeling either the apical or basolateral membrane with fluorescent probes and ascertaining 1) whether the probe can diffuse laterally in the membrane, and 2) whether it can pass through the tight junction region to the side of the cell initially not labeled. Our results show that membrane-bound lectins and some lipid probes are incapable of passing through the tight junction region. The lectins are immobile on the cell surface, but the lipid probes diffuse freely in the membrane. We propose that the ability of a lipid probe to pass through the tight junction is correlated with its ability to flip-flop to the inner monolayer of the cell membrane bilayer, and that the tight junction thus forms a barrier to lipids in the outer monolayer only. Differences in diffusion rates of different lipid probes also appear to reflect different physical characteristics of the inner versus outer membrane leaflet.