Parton Robert G, Molero Juan Carlos, Floetenmeyer Matthias, Green Kathryn M, James David E
Institute for Molecular Bioscience, Centre for Microscopy and Microanalysis, and School of Biomedical Sciences, University of Queensland, Queensland 4072, Australia.
J Biol Chem. 2002 Nov 29;277(48):46769-78. doi: 10.1074/jbc.M205683200. Epub 2002 Sep 27.
Caveolae are small invaginations of the cell surface that are abundant in mature adipocytes. A recent study (Kanzaki, M., and Pessin, J. E. (2002) J. Biol. Chem. 277, 25867-25869) described novel caveolin- and actin-containing structures associated with the adipocyte cell surface that contain specific signaling proteins. We have characterized these structures, here termed "caves," using light and electron microscopy and observe that they represent surface-connected wide invaginations of the basal plasma membrane that are sometimes many micrometers in diameter. Rather than simply a caveolar domain, these structures contain all elements of the plasma membrane including clathrin-coated pits, lipid raft markers, and non-raft markers. GLUT4 is recruited to caves in response to insulin stimulation. Caves can occupy a significant proportion of the plasma membrane area and are surrounded by cortical actin. Caveolae density in caves is similar to that on the bulk plasma membrane, but because these structures protrude much deeper into the plane of focus of the light microscope molecules such as caveolin and other plasma membrane proteins appear more concentrated in caves. We conclude that the adipocyte surface membrane contains numerous wide invaginations that do not represent novel caveolar structures but rather large surface caves.
小窝是细胞表面的小凹陷，在成熟脂肪细胞中大量存在。最近一项研究（Kanzaki, M., and Pessin, J. E. (2002) J. Biol. Chem. 277, 25867 - 25869）描述了与脂肪细胞表面相关的新型含小窝蛋白和肌动蛋白的结构，这些结构包含特定的信号蛋白。我们利用光学显微镜和电子显微镜对这些结构进行了表征，这里将其称为“洞穴”，并观察到它们代表了基底质膜表面相连的宽凹陷，其直径有时可达数微米。这些结构并非简单的小窝结构域，而是包含了质膜的所有成分，包括网格蛋白包被小窝、脂筏标记物和非脂筏标记物。在胰岛素刺激下，葡萄糖转运蛋白4（GLUT4）被募集到洞穴中。洞穴可占据质膜面积的很大一部分，并且被皮质肌动蛋白所包围。洞穴中小窝的密度与质膜上的相似，但由于这些结构在光学显微镜的焦平面上深入得多，小窝蛋白和其他质膜蛋白等分子在洞穴中显得更为集中。我们得出结论，脂肪细胞表面膜包含众多宽凹陷，这些凹陷并非新型小窝结构，而是大型表面洞穴。
