Fine Structural Basis for Hemoglobin Filtration by Glomerular Capillaries

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Abstract
The presence of filtered hemoglobin in Bowman’s space of in vivo fixed glomeruli was ascertained by microspectrophotometry and special staining of sections for light microscopy. By electron microscopy, hemoglobin appeared as a finely granular material in the lumens of glomerular capillaries and in Bowman’s space. Filtration of hemoglobin was usually unassociated with morphologic alterations in endothelial or epithelial cells. During filtration, the hemoglobin molecules seemed to traverse the endothelium across the diaphragm closing the fenestrae. Following transport through the basement membrane, the molecules gained access to Bowman’s space by passing through the filtration slit membranes between the foot processes. Uptake of hemoglobin by glomerular epithelial cells was minimal or lacking. Fusion of foot processes was noted occasionally at late intervals after the induction of hemoglobinuria; it appeared to reflect focal damage of epithelial cells, rather than a general, immediate reaction of epithelial cells to filtration of the concentrated solution of hemoprotein molecules.

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