脂质筏和质膜微囊做为细胞膜上两种特殊的脂质微区，参与了许多跨膜物质运输和膜上受体的信号转导过程。胰岛素促进的GLUT4 (glucose transporter 4，葡萄糖转运蛋白4)转位和葡萄糖摄取是高等生物调节血糖代谢的主要方式，胰岛素分泌不足或效应不足就会诱发糖尿病，目前的研究表明脂质筏和质膜微囊对这一过程也有重要的调控作用。但目前的研究方法还不能区分它们各自特异性的功能，二者通常是被等同的。为剖析二者，我们在3T3-L1脂肪细胞中采用了 RNAi的方法，通过抑制质膜微囊重要的结构蛋白Caveolin1的表达来抑制质膜微囊的形成。我们发现，Caveolin1的表达被抑制后，胰岛素受体的活化、GLUT4向细胞质膜的的转位以及葡萄糖摄取能力都没有受到损害，但是胰岛素撤除之后GLUT4的内吞过程受到了显著的抑制。我们改进了密度梯度超离心的方法，可以分离脂质筏和质膜微囊组分，发现在RNAi细胞中，依然存在着类似于质膜微囊的脂质微区结构，这揭示出质膜微囊所在的脂质微区与脂质筏存在着显著的脂质和蛋白组成差异，不仅仅是简单的结构蛋白Caveolin1的差异。我们发现在对照细胞中，胰岛素作用后，转位到质膜上的GLUT4在脂质筏和质膜微囊中均有定位，而在RNAi细胞中则主要定位于脂质筏中；而且，我们发现胰岛素撤除后，定位于质膜微囊中的GLUT4水平下降更快。综合前人和我们的结果，我们认为使用RNAi的方法更具特异性，脂质筏和质膜微囊在胰岛素受体信号转导和GLUT4运输过程中发挥着不同的作用：脂质筏主要在信号转导和GLUT4的上膜过程中发挥作用，而Caveolin1和质膜微囊则对GLUT4的有效内吞负责。 关键词：GLUT4，转位，内吞，脂质筏，质膜微囊，密度梯度超离心

 Caveolae and non-caveolar lipid rafts are two types of membrane lipid microdomains that play an important role in insulin-stimulated glucose uptake in adipocytes. However, they cannot be discriminated from each other because of the limitation of the current methods and are often equated. In order to ascertain their specific functions in the process, caveolae were ablated by caveolin-1 RNA interference. In Cav-1 RNAi adipocyte, neither insulin stimulated glucose uptake nor GLUT4 (glucose transporter 4) translocation to membrane lipid microdomains were affected by the ablation of caveolae. With a modified sucrose density gradient, caveolae and non-caveolar lipid rafts could be separated. Interestingly, the similar lipid microdomain corresponding to caveolae still existed in RNAi cells, which shed light on the speciality of the lipid and the protein compostions. In the wild type 3T3-L1 adipocyte, GLUT4 was found to be translocated into both caveolae and non-caveolar lipid rafts. However, in Cav-1 RNAi adipocyte, GLUT4 was localized predominantly in non-caveolar lipid rafts. After the removal of insulin, caveolae-localized GLUT4 was internalized faster than non-caveolar lipid rafts-associated GLUT4. The internalization of GLUT4 from plasma membrane was significantly decreased in Cav-1 RNAi adipocyte. These results suggested that insulin stimulated GLUT4 translocation and glucose uptake is a caveolae-independent event. Lipid rafts and caveolae mostly differently functioned in the regulation of GLUT4 trafficking. Lipid rafts took charge of insulin signaling and caveolae played a function in the internalization of GLUT4 from plasma membrane after the removal of insulin. Key words: GLUT4 translocation, GLUT4 internalization, lipid rafts, caveolae, sucrose density gradient flotation