SEM Observation of Mesangial Cells in the Rat Kidney by NaOH Maceration Combined with Freeze Cracking

A scanning electron microscopic study of glomerular mesangial cells was conducted in the rat kidney after freeze cracking and subsequent removal of the glomerular basement membrane and mesangial matrix with NaOH maceration. Mesangial cells extend long branching processes in accord with previous light microscopic observation by Zimmermann, and further reveal numerous short microvilli and fine grooves on their surfaces. Mesangial cells interdigitate with each other by the microvilli, forming an intercellular labyrinth. Mesangial processes are closely attached to the basal surface of the capillary endothelium. Sometimes the processes encircle the capillary for more than half of its circumference, suggesting that they might effectively regulate its caliber. Mesangial cells frequently protrude small cytoplasmic blebs into the capillary lumen, entering into direct contact with circulating blood. Goormaghtigh's cells resemble the intraglomerular mesangial cells, extending branching processes covered with microvilli and revealing labyrinthine intercellular spaces formed by the microvilli. The intercellular labyrinth among the mesangial cells and that among Goormaghtigh's cells connect with each other at the hilus, providing a channel leading from the periphery of the glomerulus through the hilus to the interstitial space outside the glomerulus