Demonstration of actomyosin in mesangial cells of the renal glomerulus.

Antisera to human uterine actomyosin were prepared in rabbits and conjugated with fluorescein (F-AUAM). When F-AUAM was applied to frozen sections of normal human kidney which were then examined by ultraviolet light microscopy, it was observed that vascular smooth muscle, endothelium of arteries, veins, and peritubular capillaries and glomerular mesangial cells were immunofluorescent. Neither glomerular endothelium nor epithelial cells of Bowman's capsule or renal tubules were stained by F-AUAM. The specificity of antisera for actomyosin was confirmed by absorption and blocking studies, examination of a wide variety of tissues and immunodiffusion in agarose gel. It may be inferred from these data that mesangial cells are contractile. Contraction of the mesangium may play a significant role in regulating glomerular blood flow and in the reaction of the glomerulus to injury.