Franke W W, Lüder M R, Kartenbeck J, Zerban H, Keenan T W
J Cell Biol. 1976 Apr;69(1):173-95. doi: 10.1083/jcb.69.1.173.
The ultrastructure of the apical zone of lactating rat mammary epithelial cells was studied with emphasis on vesicle coat structures. Typical 40-60 nm ID "coated vesicles" were abundant, frequently associated with the internal filamentous plasma membrane coat or in direct continuity with secretory vesicles (SV) or plasma membrane proper. Bristle coats partially or totally covered membranes of secretory vesicles identified by their casein micelle content. This coat survived SV isolation. Exocytotic fusion of SV membranes and release of the casein micelles was observed. Frequently, regularly arranged bristle coat structures were identified in those regions of the plasma membrane that were involved in exocytotic processes. Both coated and uncoated surfaces of the casein-containing vesicles, as well as typical "coated vesicles", were frequently associated with microtubules and/or microfilaments. We suggest that coat materials of vesicles are related or identical to components of the internal coat of the surface membrane and that new plasma membrane and associated internal coat is produced concomitantly by fusion and integration of bristle coat moieties. Postexocytotic association of secreted casein micelles with the cell surface, mediated by finely filamentous extensions, provided a marker for the integrated vesicle membrane. An arrangement of SV with the inner surface of the plasma membrane is described which is characterized by regularly spaced, heabily stained membrane to membrane cross-bridges (pre-exocytotic attachment plaques). Such membrane-interconnecting elements may represent a form of coat structure important to recognition and interaction of membrane surfaces.
研究了泌乳大鼠乳腺上皮细胞顶端区域的超微结构，重点关注囊泡被膜结构。典型的直径40 - 60纳米的“被膜小泡”数量丰富，常与内部丝状质膜被膜相关联，或与分泌小泡（SV）或质膜本身直接连续。刷毛状被膜部分或完全覆盖了根据其酪蛋白胶粒含量鉴定的分泌小泡膜。这种被膜在分泌小泡分离后仍存在。观察到分泌小泡膜的胞吐融合以及酪蛋白胶粒的释放。在参与胞吐过程的质膜区域，经常能识别出规则排列的刷毛状被膜结构。含酪蛋白的小泡的被膜和未被膜表面，以及典型的“被膜小泡”，都常与微管和/或微丝相关联。我们认为小泡的被膜物质与表面膜的内部被膜成分相关或相同，并且新的质膜和相关的内部被膜是由刷毛状被膜部分的融合和整合同时产生的。分泌的酪蛋白胶粒通过细丝状延伸与细胞表面的胞吐后关联，为整合的小泡膜提供了一个标记。描述了分泌小泡与质膜内表面的一种排列方式，其特征是有规则间隔的、染色较深的膜间交叉桥（胞吐前附着斑）。这种膜连接元件可能代表了一种对膜表面识别和相互作用很重要的被膜结构形式。
