The isoporous substructure of the human glomerular slit diaphragm.

The substructure of the human glomerular slit diaphragm is examined after perfusion fixation of a human kidney with tannic acid-glutaraldehyde. The present study shows that the substructure of the slit diaphragm in man is very similar to that described in rats and mice, and that the dimensions of the contained pores (50 times 120 A) in the human differ only slightly from those reported for the murine kidney. It is unlikely that rectangular pores of the dimensions of those measured in the human kidney would permit, under physiological conditions, the penetration of significant quantities of serum protein molecules. It is possible, therefore, that the slit diaphragm in the human glomerulus could function as a fine filter for serum proteins, although this remains to be definitely proved.