Lawson D, Raff M C, Gomperts B, Fewtrell C, Gilula N B
J Cell Biol. 1977 Feb;72(2):242-59. doi: 10.1083/jcb.72.2.242.
We have used thin section and freeze-fracture electron microscopy to study membrane changes occurring during exocytosis in rat peritoneal mast cells. By labeling degranulating mast cells with ferritin-conjugated lectins and anti-immunoglobulin antibodies, we demonstrate that these ligands do not bind to areas of plasma membrane or granule membrane which have fused with, or are interacting with, granule membrane. Moreover, intramembrane particles are also largely absent from both protoplasmic and external fracture faces of plasma and granule membranes in regions where these membranes appear to be interacting. Both the externally applied ligands and intramembrane particles are sometimes concentrated at the edges of fusion sites. The results indicate that membrane proteins are displaced laterally into adjacent membrane regions before the fusion process and that fusion occurs between protein-depleted lipid bilayers. The finding of protein-depleted blebs in regions of plasma and granule membrane interaction raises the interesting possibility that blebbing may be a process for exposing the granule contents to the extracellular space and for the elimination of excess lipid while conserving membrane proteins.
我们运用超薄切片和冷冻蚀刻电子显微镜技术，研究大鼠腹膜肥大细胞胞吐过程中发生的膜变化。通过用铁蛋白偶联凝集素和抗免疫球蛋白抗体标记脱颗粒的肥大细胞，我们证明这些配体不会与已与颗粒膜融合或正在与颗粒膜相互作用的质膜或颗粒膜区域结合。此外，在这些膜似乎相互作用的区域，质膜和颗粒膜的原生质断裂面和外表面断裂面上也基本没有膜内颗粒。外部施加的配体和膜内颗粒有时会集中在融合位点的边缘。结果表明，膜蛋白在融合过程之前横向位移到相邻的膜区域，并且融合发生在蛋白质缺失的脂质双层之间。在质膜和颗粒膜相互作用区域发现蛋白质缺失的小泡，这引发了一个有趣的可能性，即小泡形成可能是一个将颗粒内容物暴露于细胞外空间以及在保留膜蛋白的同时消除多余脂质的过程。
