Kukulies J, Komnick H
J Cell Sci. 1983 Jan;59:159-82. doi: 10.1242/jcs.59.1.159.
The cell membranes and cell junctions of the rectal chloride epithelia of the larval dragonfly Aeshna cyanea were examined in thin sections and by freeze-fracture. These epithelia function in active ion absorption and maintain a high concentration gradient between the haemolymph and the fresh-water environment. Freeze-fracturing reveals fine-structural differences in the intramembraneous particles of the luminal and contraluminal plasma membranes of these epithelia, reflecting the functional diversity of the two membranes, which are separated by the junctional complex. The particle frequency of the basolateral plasma membranes is reduced after transfer of the larvae into high concentrations of environmental salinity. The junctional complex is located in the apical region and composed of three types of cell junctions: the zonula adhaerens, seen in freeze-fracture as a nearly particle-free zone; the extended and highly convoluted pleated septate junction and randomly interspersed gap junctions of the inverted type. Gap junctions also occur between the basolateral plasma membranes. They provide short-cuts in the diffusion pathway for direct and rapid co-ordination of the interconnected cell processes. Colloidal and ionic lanthanum tracer solutions applied in vivo from the luminal side penetrate through the cuticle via epicuticular depressions, but invade only the apical portion of the junctional complex. This indicates that the pleated septate junction constitutes a structural control of the paracellular pathway across the chloride epithelia, which are devoid of tight junctions. The structure of the pleated septate junctions is interpreted as a device for the extension of the diffusion distance, which is inversely related to the net diffusion. A conservative estimate of the total length of the junction, and the number and extension of septa reveals that the paracellular route exceeds the transcellular route by a factor of 50.
采用超薄切片和冷冻蚀刻技术，对蜻蜓幼虫（大蜓）直肠氯化物上皮细胞的细胞膜和细胞连接进行了研究。这些上皮细胞具有主动离子吸收功能，并在血淋巴和淡水环境之间维持高浓度梯度。冷冻蚀刻显示，这些上皮细胞腔面膜和对腔面膜的膜内颗粒存在细微的结构差异，这反映了由连接复合体分隔的这两种膜的功能多样性。将幼虫转移到高浓度环境盐度中后，基底外侧细胞膜的颗粒频率降低。连接复合体位于顶端区域，由三种类型的细胞连接组成：黏着小带，在冷冻蚀刻中表现为几乎无颗粒的区域；延伸且高度卷曲的褶皱分隔连接以及倒置型的随机散布的间隙连接。间隙连接也出现在基底外侧细胞膜之间。它们为相互连接的细胞过程的直接和快速协调提供了扩散途径中的捷径。从管腔侧体内施加的胶体和离子镧示踪溶液通过表皮凹陷穿透角质层，但仅侵入连接复合体的顶端部分。这表明褶皱分隔连接构成了对穿过缺乏紧密连接的氯化物上皮细胞旁细胞途径的结构控制。褶皱分隔连接的结构被解释为一种延长扩散距离的装置，扩散距离与净扩散呈反比。对连接的总长度、隔膜的数量和延伸的保守估计表明，旁细胞途径比跨细胞途径长50倍。
