Primary uroepithelial cultures - A model system to analyze umbrella cell barrier function

Despite almost 25 years of effort, the development of a highly differentiat ed and functionally equivalent cell culture model of uroepithelial cells ha s eluded investigators. We have developed a primary cell culture model of r abbit uroepithelium that consists of an underlying cell layer that interact s with a collagen substratum, an intermediate cell layer, and an upper cell layer of large (25-100 mu m) superficial cells. When examined at the ultra structural level, the superficial cells formed junctional complexes and had an asymmetric unit membrane, a hallmark of terminal differentiation in bla dder umbrella cells. These cultured "umbrella" cells expressed uroplakins a nd a 27-kDa uroepithelial specific antigen that assembled into detergent-re sistant asymmetric unit membrane particles, The cultures had low diffusive permeabilities for water (2.8 x 10(-4) cm/s) and urea (3.0 x 10(-7) cm/s) a nd high transepithelial resistance (>8000 Ohm cm(2)) was achieved when 1 mM CaCl2 was included in the culture medium. The cell cultures expressed an a miloride-sensitive sodium transport pathway and increases in apical membran e capacitance were observed when the cultures were osmotically stretched, T he described primary rabbit cell culture model mimics many of the character istics of uroepithelium found in vivo and should serve as a useful tool to explore normal uroepithelial function as well as dysfunction as a result of disease.