Brown D
J Cell Sci. 1980 Aug;44:353-63. doi: 10.1242/jcs.44.1.353.
The collecting tubule of Xenopus laevis kidney is formed of two main types of cell: the socalled flask cells (or mitochondria-rich cells) and the remaining, more cuboidal epithelial cells. It has previously been shown that the flask-cell plasma membrane contains a population of elongated intramembrane particles similar to those found in mitochondria-rich cells of the toad bladder. It is now clear that the structure of the apical membrane of the remaining epithelial cells of the collecting duct is similar to the apical membrane of the amphibian urinary bladder granular cells. The P-face of the apical membrane has relatively few particles, whereas the E-face has many more. The E-face particles are of large diameter (16 nm), and many of them have an apical dense spot, which may represent a pit or depression in the particle. Such particles are not found on the lateral E-face below the level of the tight junctions. At the present time, the functional significance of these particles is unknown, but since vasopressin fails to elicit a hydrosmotic response in Xenopus laevis they are probably not involved in transepithelial water permeability. The fact that the different membrane specializations which characterize these mitochondria-rich and non-mitochondria-rich cells are found both in the bladder and the collecting tubule suggests that, at least in Xenopus, the 2 epithelia may share some common functions at the level of the apical membranes of their constituent cells.
即所谓的烧瓶状细胞（或富含线粒体的细胞）和其余的、更呈立方形的上皮细胞。先前已经表明，烧瓶状细胞的质膜含有一群细长的膜内颗粒，类似于在蟾蜍膀胱富含线粒体的细胞中发现的那些颗粒。现在清楚的是，集合管其余上皮细胞顶端膜的结构类似于两栖动物膀胱颗粒细胞的顶端膜。顶端膜的P面颗粒相对较少，而E面颗粒更多。E面颗粒直径较大（16纳米），其中许多有一个顶端致密斑，这可能代表颗粒中的一个凹陷或坑。在紧密连接水平以下的侧面E面上未发现此类颗粒。目前，这些颗粒的功能意义尚不清楚，但由于抗利尿激素未能在非洲爪蟾中引发渗透反应，它们可能不参与跨上皮水通透性。在膀胱和集合小管中都发现了这些富含线粒体和非富含线粒体细胞所特有的不同膜特化现象，这表明，至少在非洲爪蟾中，这两种上皮在其组成细胞顶端膜水平可能具有一些共同功能。
