Senda T, Okabe T, Matsuda M, Fujita H
Department of Anatomy, Osaka University Medical School, Japan.
Cell Tissue Res. 1994 Jul;277(1):51-60. doi: 10.1007/BF00303080.
The exocytotic process in the anterior pituitary secretory cells was studied using quick-freeze deep-etch electron microscopy, fluorescein-isothiocyanate-phalloidin staining, heavy meromyosin decoration, and immuno-electron microscopy. The subcortical actin filaments are distributed unevenly in the peripheral cytoplasm. Few secretory granules are seen beneath the plasma membrane in the region where the peripheral cytoplasm is occupied by numerous subcortical actin filaments. On the contrary, in the region free of the subcortical actin filaments, many secretory granules lie in contact with the plasma membrane. Thus, the subcortical actin filaments may control the approach of the secretory granules to the plasma membrane in these cells. The granule and plasma membranes that lie in close proximity are linked by intervening strands. Unfused portions of both membranes remain linked by these strands during membrane fusion and opening. These strands may be involved in membrane contact, fusion and opening during exocytosis. Annexin II (calpactin I) has been demonstrated immunocytochemically to be localized at the contact sites between the granule and plasma membranes, and is therefore a possible component of the intervening strands. Membrane fusion starts within focal regions of both membranes less than 50 nm in diameter. The plasma membrane shows inward depressions toward the underlying granules immediately before fusion. The disappearance of intramembranous particles from the exocytotic site of the membrane has not been observed.
利用快速冷冻深度蚀刻电子显微镜、异硫氰酸荧光素 - 鬼笔环肽染色、重酶解肌球蛋白标记及免疫电子显微镜技术，对垂体前叶分泌细胞的胞吐过程进行了研究。皮质下肌动蛋白丝在周边细胞质中分布不均。在周边细胞质被大量皮质下肌动蛋白丝占据的区域，质膜下方几乎看不到分泌颗粒。相反，在没有皮质下肌动蛋白丝的区域，许多分泌颗粒与质膜接触。因此，皮质下肌动蛋白丝可能控制这些细胞中分泌颗粒与质膜的靠近。紧密相邻的颗粒膜和质膜由中间的条索相连。在膜融合和开口过程中，两层膜未融合的部分通过这些条索保持相连。这些条索可能参与胞吐过程中的膜接触、融合和开口。免疫细胞化学已证实膜联蛋白II（钙结合蛋白I）定位于颗粒膜和质膜的接触部位，因此可能是中间条索的组成成分。膜融合在直径小于50 nm的两层膜的局部区域开始。就在融合前，质膜向下方的颗粒呈现向内凹陷。未观察到膜的胞吐部位膜内颗粒消失。
