All cells are capable of sampling their environment through a process called endocytosis. Endocytosis is involved in diverse aspects of cellular physiology including responses to growth factors, catabolism of internalized nutrients, processing of antigens during immune reactions, and maintenance of cell polarity. During endocytosis both cellular membrane as well as extracellular fluid are internalized and then transported to various intracellular compartments. We are interested in delineating these compartments, determining in which compartments different membrane components and fluid are sorted from one another, and analyzing the regulatory mechanisms that control membrane flow into and out of these compartments. Polarized epithelial cells have increased complexity because they are capable of internalizing macromolecules from either of their discrete apical and basolateral plasma membrane domains. Current projects in the laboratory include analyzing the role of a specialized apical endosome involved in receptor recycling and transcytosis (the apical recycling endosome), dissecting the role of the actin cytoskeleton and the small G-proteins rho and rac in regulating endosomal traffic, and understanding the cellular regulatory and sorting machinery in permeabilized epithelial cells. Moreover, we have recently established a primary cell culture model of bladder uroepithelium and are analyzing the stretch-induced fusion of fusiform vesicles with the apical cell surface of the specialized umbrella cells that line the urinary bladder.