Indentations of the glomerular basement membrane in renal diseases. A light and electron microscopic study on ultrathin serial sections.
Indentations of the glomerular basement membrane were observed by light microscopy in ultrathin Epon-embedded serial sections from the renal biopsies of patients who had membranous glomerulonephritis, minimal change glomerulonephrits, acute or resolving exudative glomerulonephritis and focal glomerulonephrits, interstitial nephritis, amyloidosis, rheumatoid arthritis, or ankylosing spondylitis. In patients with membranous glomerulonephritis, acute or resolving exudative glomerulonephritis, amyloidosis, or rheumatoid arthritis, the occurrence of indentations in the glomerular basement membrane differed significantly from that in controls. The presence of indentations did not correlate with proteinuria, hematuria, leukocyturia, arterial hypertension, or with the nephrotic syndrome or its treatment with steroids. Examination of alternate serial sections by light and be electron microscopy showed that the indentations that were light microscopically visible corresponded to craters on the epithelial surface of the glomerular basement membrane seen in the electron microscope. These craters contained protruding portions of the epithelial cells, extracellular electron-lucent material or electron-dense amorphous or striated membranous material. They were often surrounded by spikelike protrusions of the lamina densa. These indentations might represent solitary remnants of former subepithelial deposits.