Lipid rafts are localized liquid-ordered regions of the plasma membrane that contain high levels of cholesterol and glycosphingolipids, and are resistant to extraction with nonionic detergents. Retinal photoreceptor cells contain detergent-resistant membrane microdomains (DRM), which were isolated here from bovine rod outer segments (ROS) under dark and light conditions. Rhodopsin (R) was present in both DRM and detergent soluble fractions (DSF), and detergent-insoluble ROS rafts were enriched in caveolin 1 (Cav-1) and c-Src. In the dark, arrestin and its 44-kDa truncated form (p44) were present mainly in DSF; however, p44 was translocated to DRM under illumination. Similarly, transducin (T) was mainly present in DSF in the dark, but it was recruited toward the DRM fraction following photolysis. DRM were also prepared in the absence or presence of Mg-ATP, guanosine 5′-3-O-(thio)triphosphate (GTPγS), or both. Although GTPγS released T into DSF in the light, GTPγS-activated T was retained in DRM when Mg²⁺ and ATP were added. Moreover, T was always tyrosine-phosphorylated under light conditions, which suggested that T phosphorylation prevents its GTPγS-induced release from DRM. In addition, treatment with the tyrosine kinase inhibitor genistein prevented the segregation of T to the rafts. In contrast, no localization difference was seen in the presence of Mg-ATP for Cav-1, c-Src, R and both forms of arrestin. Interestingly, immunoprecipitation assays followed by Western blot analyses under light conditions showed the formation of multimeric complexes containing R, T, c-Src, p44 and Cav-1 in DRM, where T and c-Src were tyrosine-phosphorylated.

脂质筏是质膜的局部液体有序区域，包含高水平的胆固醇和鞘糖脂，并且对非离子型去污剂的提取具有抵抗力。视网膜感光细胞包含耐去污剂的膜微区（DRM），此处在黑暗和明亮条件下从牛杆外段（ROS）中分离出来。视紫红质（R）存在于DRM和去污剂可溶性馏分（DSF）中，去污剂不溶性ROS筏中富含小窝蛋白1（Cav-1）和c-Src。在黑暗中，抑制蛋白及其44 kDa的截短形式（p44）主要存在于DSF中。然而，p44在光照下易位至DRM。同样，转导素（T）主要在黑暗中存在于DSF中，但在光解后被募集至DRM组分。O-（硫代）三磷酸酯（GTPγS），或两者兼而有之。尽管GTPγS在光线下将T释放出T，但是当添加Mg ²⁺和ATP时，GTPγS激活的T保留在DRM中。此外，T在光照条件下总是被酪​​氨酸磷酸化，这表明T磷酸化阻止了其GTPγS诱导的DRM释放。另外，用酪氨酸激酶抑制剂染料木黄酮处理可防止T向木筏分离。相反，对于Cav-1，c-Src，R和两种形式的抑制蛋白，在Mg-ATP存在下均未见定位差异。有趣的是，免疫沉淀测定法和随后在轻条件下进行的蛋白质印迹分析表明，DRM中形成了含有R，T，c-Src，p44和Cav-1的多聚体复合物，其中T和c-Src被酪氨酸磷酸化。