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

1.在活性吸收上皮细胞（肾近端小管、输出小管和内脏卵黄囊）的顶端细胞质区观察到许多膜性小管。这些小管经常与内体连接，形成顶管-内体复合物。示踪实验表明，顶小管是由内体出芽形成的，并在膜再循环中发挥作用.用含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。螺旋结构是一个左手四重螺旋，其中每一股由螺旋缠绕的平行行（约200）。11 nm的直径），在接近顶小管圆柱体的限制膜（约。直径80 nm）。11个颗粒构成了每个螺旋的一整圈，螺距为60 nm。这些粒子围绕着一个电子透明的圆柱体（ca。直径38 nm），在其中心含有另一组单行的小颗粒（约38 nm）。9 nm直径）。基于连续薄切片的追踪的顶端小管-内体复合物的计算机辅助三维重建显示，20-40%的膜驻留在小管部分中，而体积为5-10%。这一结果表明，在膜回收的高效率的顶端小管。在电子显微镜水平上对顶小管的化学性质进行的分析表明，顶小管含有高浓度的碳水化合物，并且形成管腔特化的材料由蛋白质组成，该蛋白质容易被蛋白水解酶消化。使用几种凝集素的进一步研究表明，顶端小管含有N-乙酰葡糖胺或唾液酸作为碳水化合物组分。

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.