Radial gradient culture on the inner surface of collagen tubes: organoid growth of normal rat bladder and rat bladder cancer cell line NBT-II.

Radial histophysiologic gradient culture uses thin walled, permeable collagen tubes to house inocula in the form of either tissue explants, aggregates of cells, or dissociated cells. The outgrowth from these inocula spreads on the inner surface of the cylindrical tube, completely lining the lumen. Metabolites are exchanged through the wall of the collagen tube by diffusion from the pool of medium surrounding the cylinder. Urothelial cells form organoid stratified epithelium. A histophysiologic gradient occurs with the basal surface of the epithelium attached to the collagen wall. At this interface, for normal bladder, the initiation of epithelial renewal is seen in the basal zone, as shown by incorporation of tritiated thymidine. The simulation of conditions in nature is attained by the exchange of metabolites between the pool of medium and the basal zone of the epithelium. NBT-II appears as two concentric stratified epithelia. Isotopic labelling is seen throughout the epithelium attached to the collagen membrane. In the superficial stratified epithelium remnants of nuclei are seen without isotopic labelling. Preparation of living cultures and, after fixation, of histologic sections is technically easy.