Burton P R
J Cell Biol. 1984 Aug;99(2):520-8. doi: 10.1083/jcb.99.2.520.
The substructure and distribution of luminal material in microtubules of olfactory axons were studied in the bullfrog, Rana catesbeiana. By using numerous fixation methods, with and without osmium tetroxide, the luminal component was shown not to be an artifact of fixation. The material consists of globular elements 4-5 nm in diameter loosely arranged within the lumen in a discontinuous column. Counts of microtubules showing luminal material were obtained for axons in the proximal and distal ends of the olfactory nerve, and it was found that 16-18% more of the microtubules in the distal regions showed the luminal component. This raises the possibility that the material might be translocated within the microtubule lumen and tends to accumulate as it moves distally toward the axon terminal. In contrast to those of the olfactory axons, microtubules assembled in vitro from frog brain tubulin did not show luminal material. When microtubules in olfactory axons were depolymerized in situ by cold and calcium treatment and then induced to reassemble, most of those that were formed de novo showed empty lumina. Such evidence suggests that the luminal material is not an integral component of the microtubule. The hypothesis is discussed that material may be translocated within the lumina of microtubules. Furthermore, in the case of neuronal microtubules, the possibility is raised that they may serve as conduits for their own wall subunits.
在牛蛙（Rana catesbeiana）中研究了嗅觉轴突微管腔内物质的亚结构和分布。通过使用多种固定方法，包括使用和不使用四氧化锇，结果表明腔内成分并非固定过程产生的假象。该物质由直径为4 - 5纳米的球状成分组成，在管腔内以不连续的柱状松散排列。对嗅觉神经近端和远端轴突中显示有腔内物质的微管进行了计数，发现远端区域显示有腔内成分的微管比近端多16 - 18%。这增加了一种可能性，即该物质可能在微管腔内移位，并在向轴突末端远端移动时倾向于积累。与嗅觉轴突的微管不同，由蛙脑微管蛋白在体外组装的微管未显示有腔内物质。当通过冷处理和钙处理使嗅觉轴突中的微管原位解聚，然后诱导其重新组装时，大多数新形成的微管显示为空的管腔。这些证据表明腔内物质不是微管的一个组成部分。文中讨论了物质可能在微管腔内移位的假说。此外，对于神经元微管而言，还提出了它们可能作为自身管壁亚基的通道的可能性。
