GLOMERULAR EPITHELIAL FOOT PROCESSES AND FILTRATION SLITS IN IDDM PATIENTS

Diabetic nephropathy is associated with functional changes in the glom erular filtration barrier but the structural counterpart remains unkno wn. Width of glomerular epithelial cell foot processes and of filtrati on slits were determined by morphometric methods in 11 non-diabetic ki dney donors and in 28 diabetic patients with albumin excretion rates r anging from normal to proteinuria. Foot process width was estimated fr om the ratio of tuft surface density to length density of slits. At hi gh magnification independently sampled, perpendicularly cut slits were classified. Foot process width on peripheral basement membrane was in creased in microalbuminuric compared to normoalbuminuric diabetic pati ents (p < 0.05) but showed no significant correlation with the level o f albumin excretion when patients with increased barrier permeability were considered. Width of filtration slits in normo- and microalbuminu ric diabetic patients exceeded that in nondiabetic control subjects (p < 0.05). Filtration slits were narrower in patients with overt protei nuria than in patients with microalbuminuria (p < 0.05) and correlated with glomerular filtration rate in all of the diabetic patients (r = 0.65, p < 0.005). The results show that insulin-dependent diabetic pat ients with nephropathy present changes of epithelial cells and filtrat ion slits, demonstrable already in the stage of microalbuminuria. The mechanism of albumin leakage is not achieved by these measures. The di mension of filtration slits may play a contributing role in the level of glomerular filtration rate in diabetic patients.