Scanning electron microscopy of the glomerular filtration membrane in the rat kidney

Abstract

The rat kidney was perfused with saline and glutaraldehyde, treated with Murakami's tannin-osmium impregnation method, ethanol-freeze cracked and dried by the critical point method. Gold-palladium evaporated specimens were observed in a field-emission scanning electron microscope. The glomerular filtration membrane, fractured in different planes was observed with the following results: 1. Adjacent pedicles originate from different podocytes. No interpedicular bridges of apparent cytoplasmic nature could be found. 2. The basement membrane, in grazing fractures shows a horizontally layered architecture. 3. The attenuated endothelial sheet (lamina fenestrata) is divided into compartments, which we suggest should be called "areolae fenestratae", by cytoplasmic crests radiating from the nucleated portion of the endothelial cell. A crest also occurs along the cell margin, which contacts a similar crest at the margin of the adjacent cell. 4. The pores in the areolae fenestratae are variable in size (30-150 nm diameter). A knob-like projection from the apparently naked basement membrane is found in a portion of the pores. 5. Numerous microvilli may occur on the endothelium. Some of them anastomose and fuse with one another to form a net whose meshes appear identical with the endothelial pores. Domes and shelves formed of a fenestrated cytoplasmic sheet also occur above the ordinary level of the endothelial lining. A hypothesis implicating microvilli in the partial renewal of the endothelial sheet is proposed.

A transmission electron microscopic study on sinusoidal cells of guinea pig liver, with special reference to the occurrence of a canalicular system and "pored domes" in the endothelium.

“…In four of the six adult guinea pigs examined, the following were revealed in the sinusoidal endothelial cell of the liver: 1) the occurrence of lipid droplets and 2) of the tortuous canalicular system in the cytoplasm as well as 3) the so-called "pored domes" (FuJITA et al, 1976;YosHINAUI and FUJITA, 1982). In TEM preparations, lipid droplets are preserved, moderately blackened by osmic acid.…”

“…By using a scanning electron microscope (SEM), FUJITA et al (1976) revealed, in a fenestrated glomerular endothelial sheet (lamina f enestra or areolae fenestratae) of the rat kidney, domes and shelves formed of a f enestrated cytoplasmic sheet above the ordinary level of the endothelial lining, and proposed a hypothesis that they might be formed by the anastomosis of microvilli and thus be involved in the replacement of depleted parts of the aleolae fenestratae. Thereafter, Y0sHINARI and FUJITA (1982) used SEM to observe the glomerular endothelium in the rabbit kidney, and revealed the domes both on the aleolae fenestratae and on the perikaryonal swelling, designating them as the "pored domes.…”

Stratified laminae fenestratae (alveolus fenestratus endothelialis) in the glomerular capillaries of the mouse kidney.

“…Previous studies have noted the regional abundance of microvilli on the luminal surface of the endothelium, and the occasional fusing of the top of the microvilli has been described (FUJITA et al, 1976;FUJITA and MIYOSHI, 1985). These findings suggest that active and repeated budding and fusion of the microvilli from the endothelial surface may result in the formation of this structure.…”

“…The structure of a typical, single-layered lamina or areola fenestrata of the glomerulus has been fully described by several authors using both transmission and scanning electron microscopy (YAMADA, 1955;FUJITA et al, 1976;FUJITA and MIYOSHI, 1985). The present findings were in good accordance with those already described.…”

Perisinusoidal cells in a three-dimensional organization of the adrenal cortex in the monkey.

“…5). The structural meaning of the processes is not known at present, though this type of processes has been previ- ously reported in the glomerular capillaries and regarded as a precursory structure for partial renewal of the sieve plate of the endothelial cytoplasm (WOLFF, 1966;WOLFF and MERKER, 1966;FUJITA et al, 1976;YOSHINARI and FUJITA, 1982).…”