Aspects of the Ultrastructure of the Brush Border of the Kidney of Normal Mouse

In spite of the intensive research which has been carried out on the kidney, little is actually known about the ultrastructure of the brush border. This preliminary note refers to a structural detail of the brush border found in the proximal convolution of the nephrons in normal mouse kidney, as studied under the electron microscope. Normal mice were decapitated and immediately afterwards the kidney was exposed, stripped from its capsule, and a thin slice of its cortex was fixed for electron microscopy (Palade, 1952). The rest of the technique was routine. The material was examined at a Siemens electron microscope t~M 100b model. Micrographs were taken at original enlargements of 1,200, 7,200, and 15,000. The appearance of the brush border of all cells is basically the same as described by different authors (Sj6strand and Rhodin, 1953; P, hodin, 1954; Pease, 1955; Policard, 1957; and others), with the exception that in a few digitations (microvilli) of some brush borders, infoldings of the membrane (Fig. 1, A) and vesicles (Fig. 1, B) with an apparently dense content can be visualized. These vesicles, which measure about 200 A, are disposed along the middle of the units of the brush border (Figs. 1,C and 1,D). Fig. 3, at A, shows the same aspect in a somewhat less marked form. Fig. 2 is an