Derivation and termination of fusiform vesicles in the transitional epithelium of the rat urinary bladder

Ultrastructural behavior of fusiform vesicles with an asymmetrical unit membrane in the rat transitional epithelium was investigated by in situ injection of gold colloidal particles and gold-labeled Ricinus communis lectin, and by section staining with the lectin. These experiments suggest that the fusiform vesicles are not formed from the luminal cell membrane by contraction of the urinary bladder, and that old luminal cell membranes are removed via multivesicular bodies.