Evidence for the blood-urine barrier depending on urothelium and carbonic anhydrase positive fibroblasts.
A subepithelial multilayer of abundant fusiform cells has been distinguished cytochemically in the urinary bladder and ureter in mice and rats. These distinctive cells stained selectively for carbonic anhydrase (CA) isozymes I and III. Immunonegativity for keratin and Na+,K+-ATPase differentiated the CA-positive cells from epithelial cells and their lack of immunoreactivity for actin distinguished them from smooth muscle cells. Immunostaining for vimentin, blue staining with the trichrome method, location in an exceptionally dense collagen stroma, and ultrastructural appearance related the multilayer cells to fibroblasts. A loosely collagenous, less cellular lamina propria separated the CA-positive suburothelial zone from the smooth muscle wall in the rodent urinary bladder. Ureter lacked the loose lamina propria, and the presence of such a collageneous layer in bladder therefore correlated with distensability of the organ. The presence of CA uniquely in the fibroblastoid cells applied intimately to ureter and bladder epithelium implies a specialized function of these cells, possibly one concerned with the barrier between blood and hypertonic urine. Cytochemical demonstration of keratin and fucose-rich glycoconjugate in the plasmalemma of superficial urothelial cells indicates a role for these components in passively maintaining the blood-urine barrier. The observed distribution of Na+,K+-ATPase in mid and deep urothelial cells implicates this enzyme and these cells in actively maintaining the urine's hypertonicity. Basal urothelial cells contained glycoconjugate with terminal galactose in their plasmalemma. Ultrastructural features suggesting involution of superficial urothelial cells further evidence restriction of active ion transport to the deeper cells.
D000818:Animals; D001769:Blood; D002256:Carbonic Anhydrases / Q000032:analysis*; D005347:Fibroblasts / Q000201:enzymology*; D006651:Histocytochemistry; D007633:Keratins / Q000032:analysis; D051379:Mice; D008854:Microscopy, Electron; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis; D014513:Ureter / Q000201:enzymology; D001743:Urinary Bladder / Q000201:enzymology*; D014556:Urine
D007633:Keratins; D002256:Carbonic Anhydrases; D000254:Sodium-Potassium-Exchanging ATPase