Membranous remodeling of basal infoldings in attenuated epithelial cells of dilated renal tubules under unilateral ureteral obstruction (UUO) in adult mouse kidney.

Under unilateral ureteral obstruction (UUO) in mouse kidneys, comparing proximal and distal tubules and collecting ducts, the distal tubules exhibited the most pronounced dilation and epithelial attenuation. Basal infoldings, typically well-developed in normal distal tubule cells, were infrequently present. Instead, the cell base was predominantly covered by flat-contoured plasma membranes interspersed with clusters of palisade-aligned thin cytoplasmic processes. These processes resembled the mitochondria-free terminal portions of cytoplasmic processes normally enclosed by basal infolding membranes in normal distal tubule cells. Some process clusters were enclosed by internal extensions of adjacent flat-contoured membranes, forming process-containing membranous sacs partially open to the basal interstitial space. Similar membranous bodies were observed deep within the cells, with some opening to intercellular spaces through fusion with lateral cell membranes. These membrane modifications likely represent the morphological sequence of membrane dynamics, providing additional membranes to compensate for the increased basal surface area in dilated tubules. Similarly, the collecting ducts dilated with attenuated epithelia and the basal surfaces were covered by flat-contoured plasma membranes with sparse clusters of palisade-aligned processes, suggesting basal infoldings, which also serve as a membrane supply to basolateral surfaces in these cells. However, membranous sacs containing thin processes were less frequent in collecting duct cells, indicating a less extensive membrane remodeling process compared with distal tubule cells. On the other hand, the proximal tubules exhibited the lowest luminal dilation and epithelial attenuation, and the replacement of the diminished basal infoldings by flat membranes was less frequently encountered.