Electron Microscopic Cytochemistry and Immunocytochemistry on the Structural Differentiations in the Apical Tubular System of Absorbing Epithelia

1. 在活性吸收上皮的顶端细胞质区（肾近端小管、隐管和内脏卵黄囊）可见许多膜状小管。这些小管经常与核内体相连，形成顶小管-核内体复合体。示踪实验表明，根尖小管是由核内体出芽形成的，在膜循环中起作用。通过使用含有醛和四氧化锇的固定剂，在根尖小管中发现了特殊的螺旋结构。螺旋结构为左旋四螺旋，每条螺旋链由螺旋损伤平行行（直径约11 nm）组成，平行行靠近顶管圆柱体的限制膜（直径约80 nm）。11个粒子组成了每个螺旋的一整圈，螺距为60纳米。这些粒子围绕着一个直径约38纳米的电子发光圆柱体，圆柱体的中心包含另一组单排小粒子（直径约9纳米）。基于连续薄切片示踪的根尖小管-核内体复合体的计算机辅助三维重建显示，20-40%的膜位于小管部分，而体积为5-10%。这一结果说明了膜顶小管在膜循环中的高效率。在电子显微镜下对根尖小管化学性质的分析表明，根尖小管含有高浓度的碳水化合物，形成管腔特化的物质是由蛋白质组成的，这些蛋白质很容易被蛋白质水解酶消化。使用几种凝集素的进一步研究表明，根尖小管含有n -乙酰葡萄糖胺或唾液酸作为碳水化合物成分。

1. Many, membranous tubules were observed in the apical cytoplasmic region of active-absorptive epithelia (kidney proximal tubule, ductuli efferentes and visceral yolk sac). These tubules frequently connected with endosomes forming an apical tubule-endosome complex. A tracer experiment showed that the apical tubules were formed by budding off from the endosomes and play a role in membrane recycling.2. Specific helical structure was discovered in the apical tubules by using a fixative containing both aldehydes and osmium tetroxide. The helical structure was a left-handed quadruple helix, each strand of which consisted of helically wounded parallel rows (ca. 11 nm in diameter) in close proximity to the limiting membrane of the apical tubule cylinder (ca. 80 nm in diameter). Eleven particles constituted one full turn of each helix with a pitch of 60 nm. These particles surrounded an electron-lucent cylinder (ca. 38 nm in diameter), containing at its center another set of a single row of small particles (ca. 9 nm in diameter).3. Computer aided three-dimensional reconstruction of the apical tubule-endosome complex based on tracing of serial thin sections showed that 20-40% of the membrane reside in the tubule portion in contrast to 5-10% of the volume. This result suggests the high efficiency of the apical tubules in the membrane recycling.4. An analysis of the chemical nature of the apical tubules at electron microscopic levels demonstrated that the apical tubules contain a high concentration of carbohydrates and the material which forms the luminal specializations is composed of proteins, which are readily digested by a proteolytic enzyme. A further investigation using several lectins showed that the apical tubules contain N-acetylglucoseamine or sialic acid as a carbohydrate component.