Cooper N G, McLaughlin B J
J Comp Neurol. 1984 Dec 10;230(3):437-43. doi: 10.1002/cne.902300311.
The polyene antibiotic filipin, which binds to membrane sterols, has been used to investigate the relative distribution of cholesterol at photoreceptor synaptic junctions in the chick retina. Following anesthesia and aldehyde perfusion fixation, the retina is removed and immersed in fixative solution containing the filipin for 36-48 hours. The retinas are then processed for freeze-fracture. Electron microscopy of freeze-fracture replicas demonstrates that the filipin-sterol complexes are not evident between intramembrane particles of the presynaptic and postsynaptic particle arrays that are present at ribbon and basal junctions. In contrast, the synaptic vesicle fusion zone of ribbon junctions contains large numbers of filipin-sterol complexes which are observed merging with the free margins of the presynaptic particle array. There is a scarcity of such complexes, however, around the free margins of basal junction presynaptic particle arrays. These latter sites do not contain a vesicle fusion zone. Particle-poor areas of membrane that surround postsynaptic particles arrays of ribbon and basal junctions also do not contain filipin binding sites. The nonsynaptic membrane of photoreceptor terminals contains large numbers of filipin-sterol complexes, less tightly packed than in the synaptic vesicle fusion zone. Coated vesicle fusion sites in the presynaptic membrane contain groups of intramembrane particles but the filipin-sterol complexes are excluded from these sites. The observations suggest that synaptic membrane domains which interact with cytoskeletal components, such as clathrin and pre- and postsynaptic densities contain less cholesterol than other domains such as the synaptic vesicle fusion zones.
多烯抗生素制霉菌素能与膜固醇结合，已被用于研究鸡视网膜光感受器突触连接处胆固醇的相对分布。麻醉和醛灌注固定后，取出视网膜并浸入含有制霉菌素的固定液中36 - 48小时。然后对视网膜进行冷冻断裂处理。冷冻断裂复制品的电子显微镜观察表明，在带状和基底连接处存在的突触前和突触后颗粒阵列的膜内颗粒之间，制霉菌素 - 固醇复合物不明显。相比之下，带状连接处的突触小泡融合区含有大量制霉菌素 - 固醇复合物，观察到它们与突触前颗粒阵列的自由边缘融合。然而，在基底连接处突触前颗粒阵列的自由边缘周围，这种复合物很少。后一种部位不包含小泡融合区。围绕带状和基底连接处突触后颗粒阵列的膜的颗粒贫乏区域也不包含制霉菌素结合位点。光感受器终末的非突触膜含有大量制霉菌素 - 固醇复合物，其堆积程度比突触小泡融合区松散。突触前膜中的有被小泡融合位点含有膜内颗粒群，但制霉菌素 - 固醇复合物被排除在这些位点之外。这些观察结果表明与细胞骨架成分相互作用的突触膜结构域，如网格蛋白以及突触前和突触后致密物，所含胆固醇比其他结构域如突触小泡融合区少。
