Department of Biomolecular Imaging, Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
Traffic. 2010 Jan;11(1):138-50. doi: 10.1111/j.1600-0854.2009.01008.x.
Caveolae are invaginations of the plasma membrane involved in multiple cellular processes, including transcytosis. In this paper we present an extensive 3-D electron tomographic study of the endothelial caveolar system in situ. Analysis of large cellular volumes of (high-pressure frozen, freeze-substituted and epon-embedded) human umbilical vein endothelial cells (HUVECs) provided a notable view on the architecture of the caveolar system that comprises--as confirmed by 3-D immunolabeling for caveolin of 'intact' cells--bona fide caveolae, free plasmalemmal vesicles, racemose invaginations and free multi-caveolar bodies. Application of template matching to tomograms allowed the 3-D localization of caveolar membrane coatings in a robust manner. In this way we observed that bona fide endothelial caveolae, cryofixed and embedded in their cellular context, show a spiral organization of the coating as shown in the past for chemically fixed and freeze-etched caveolae from fibroblasts. Meticulous 3-D analysis further revealed that the coatings are distributed in triads of spirals over the caveolar bulb and neck. Remarkably, this coating distribution is consistently present over the membranes of the other members of the caveolar system in HUVECs. The novel observations that we present clarify the ultrastructural complexity of the 'intact' caveolar system, setting a detailed morphological basis for its functional diversity.
小窝是质膜内陷的结构，参与多种细胞过程，包括跨细胞转运。本文通过对原位内皮细胞小窝系统的广泛三维电子断层扫描研究，分析了（高压冷冻、冷冻替代和环氧树脂包埋）人脐静脉内皮细胞（HUVEC）的大细胞体积，提供了对小窝系统结构的显著认识，该系统包括通过对“完整”细胞的窖蛋白的三维免疫标记证实的真正的小窝、游离质膜囊泡、轮生内陷和游离多小窝体。模板匹配在断层扫描中的应用允许以稳健的方式对小窝膜涂层进行三维定位。通过这种方式，我们观察到在冷冻固定和嵌入细胞环境中的真正的内皮小窝显示出涂层的螺旋组织，如过去从成纤维细胞中化学固定和冷冻蚀刻的小窝所显示的那样。细致的三维分析进一步揭示了涂层在小窝球和颈部的螺旋三联体上分布。值得注意的是，这种涂层分布在 HUVEC 中小窝系统其他成员的膜上始终存在。我们提出的新观察结果阐明了“完整”小窝系统的超微结构复杂性，为其功能多样性奠定了详细的形态学基础。
