Pfenninger K H, Friedman L B
Department of Cellular and Structural Biology, University of Colorado School of Medicine, Denver 80262.
Brain Res Dev Brain Res. 1993 Feb 19;71(2):181-92. doi: 10.1016/0165-3806(93)90170-f.
Studies on plasmalemmal expansion in isolated nerve growth cones identified large, clear vesicles characteristically found in growth cones as the plasmalemmal precursor. The present article examines these plasmalemmal precursor vesicles (PPVs) in greater detail in the intact cell. (a) Pulse-chase experiments with the phospholipid precursor, [3H]glycerol, followed by radioautographic analysis show that PPVs in distal neurites and growth cones are labeled prior to equilibration of the label with the plasmalemma. (b) Pulse-chase experiments with lectin-ferritin conjugates demonstrate that PPVs are not endocytotic, that they contain lectin receptors, and that, during growth, patches of lectin receptors appear on the plasmalemma covering PPV clusters. (c) Freeze-fracture studies show that this plasmalemma shares with PPVs a paucity of intramembrane particles. (d) Lectin labeling experiments and freeze-fracture analysis demonstrate, furthermore, that the plasmalemma forms a network of invaginations at the base of PPV clusters. (e) Correlative studies indicate that the refractive 'vacuoles' seen in growth cones by phase-contrast light microscopy correspond to the PPV clusters seen at the ultrastructural level. These results confirm the identity of the plasmalemmal precursor in the intact cell and demonstrate that PPV clusters form distinct, dynamic organelles specialized for plasmalemmal expansion in the growth cone.
对分离的神经生长锥中质膜扩张的研究表明，生长锥中特有的大而清晰的囊泡是质膜的前体。本文在完整细胞中更详细地研究了这些质膜前体囊泡（PPV）。（a）用磷脂前体[3H]甘油进行脉冲追踪实验，随后进行放射自显影分析，结果显示远端神经突和生长锥中的PPV在标记与质膜平衡之前就被标记了。（b）用凝集素 - 铁蛋白偶联物进行脉冲追踪实验表明，PPV不是内吞性的，它们含有凝集素受体，并且在生长过程中，凝集素受体斑块出现在覆盖PPV簇的质膜上。（c）冷冻蚀刻研究表明，这种质膜与PPV一样，膜内颗粒较少。（d）此外，凝集素标记实验和冷冻蚀刻分析表明，质膜在PPV簇的基部形成了一个内陷网络。（e）相关研究表明，相差光学显微镜下在生长锥中看到的折射“液泡”与超微结构水平上看到的PPV簇相对应。这些结果证实了完整细胞中质膜前体的身份，并表明PPV簇形成了专门用于生长锥质膜扩张的独特动态细胞器。
