Umbrella cells are the outermost cell layer of the the urothelium, a stratified epithelium that lines the renal pelvis, ureters, and bladder. These cells form a tight barrier that prevents solute flow and toxic metabolites in the urine from entering the underlying blood supply. Components of this barrier include tight junctions and an apical membrane with a specialized lipid and protein composition. An important aspect of the umbrella cell barrier is that it must accommodate large changes in volume as the bladder fills and empties. One mechanism used by these cells is massive exocytosis of a large population of subapical discoidal/fusiform vesicles (DFVs), which significantly increases the apical surface area of the cell. Coupled with changes in cell shape and expansion of the tight junction ring, the increased apical surface area allows for increased urine storage. Upon voiding, the added apical membrane must be recovered, a process we have shown is mediated by a clathrin-independent endocytic pathway that is regulated by the dynamin GTPase, RhoA, and the beta1 integrin. Some of our current research projects include: defining the mechanosensors and signal transduction cascades that occur in response to stretch; exploring the regulatory Rab GTPases, their effectors, and how stretch regulates these Rab-dependent signaling cascades; revealing how membrane stretch is coupled to integrin signaling and stimulation of the endocytic machinery; exploring the fate of endocytosed membrane and fluid in umbrella cells.