Heterogeneity of the podocyte membrane in rat kidney as revealed by ethanol dehydration of unosmicated specimens.

The ultrastructure of the podocyte membrane was studied by means of transmission electron microscopy of unosmicated tissue samples after acetone or ethanol dehydration and subsequent embedding in a polyester resin. The podocyte membrane in glutaraldehyde (GA)-fixed, acetone-dehydrated samples consisted of a relatively thick, clear layer (about 6 nm) abutted by the dark staining cytoplasm and a dark surface layer. In GA-fixed, ethanol-dehydrated samples a striking intramembranous pattern was observed in the podocyte cell membrane. The luminal podocyte membrane was regularly perforated by gaps about 25 nm wide. In grazing sections these gaps appeared round and were separated by a honeycomb pattern of intact membrane. The abluminal membrane, in contrast, generally maintained its continuity. The clear layer of the podocyte membrane was thinner in ethanol-dehydrated samples than in acetone-dehydrated ones. In tissue samples fixed with GA supplemented by ruthenium red, ethanol dehydration was not associated with cell-membrane perforations. Based on these observations as well as on biochemical data from the literature we suggest that in GA-fixed, unosmicated, acetone-dehydrated samples the structural integrity of the podocyte membrane is well preserved, while ethanol dehydration extracts some specific material from regularly distributed domains in the podocyte cell membrane.