Light-microscopic demonstration of myoid fibrils in renal epithelial, mesangial and interstitial cells

In kidney sections treated with the tannic acid-phosphomolybdic acid-Levanol fast cyanine 5RN procedure, myoid fibrils were observed in tubular and glomerular cells. The myoid fibrils in tubular epithelial cells were delicate in normal kidneys, but became conspicuous under pathological conditions. Under certain conditions myoid fibrils were found in capsular epithelium and mesangial cells of glomeruli; in some cases podocytes also contained prominent myoid fibrils. There seemed to be a continuous system of myoid fibrils from the media of the afferent arteriole into the mesangium and through the capsular into the tubular epithelium. These myoid fibrils could not be identified with certainty in sections treated with conventional staining methods. Correlations of light-microscopic observations with electron-microscopic data indicate that the myoid fibrils in renal epithelial cells visualized by the TP-Levanol fast cyanine 5RN stain correspond to the myofilamentous system described in electron-microscopic studies by Pease (1968a). The myoid fibrils in tubular and capsular epithelial cells resembled the long forgotten 'Basalreifen' described around the turn of the century. A review of the literature shows that structures corresponding to the basal myoid fibrils were known to early histologists and that contractile functions had been suggested.