Membrane recycling and epithelial cell function.

The plasma membrane composition of virtually all eucaryotic cells is established, maintained, and modified by the process of membrane recycling. Specific plasma membrane components are inserted by exocytosis of transport vesicles, and are removed by endocytosis of segments of the membrane in which particular proteins are concentrated. In the kidney collecting duct, vasopressin induces the cycling of vesicles that are thought to carry water channels to and from the apical plasma membrane of principal cells, thus modulating the water permeability of this membrane. In the intercalated cells of the collecting duct, hydrogen ion secretion is controlled by the recycling of vesicles carrying proton pumps to and from the plasma membrane. In both cell types, "coated" carrier vesicles are involved, but whereas clathrin-coated vesicles participate in water channel recycling, the vesicles in intercalated cells are coated with the cytoplasmic domains of proton pumps. Following a brief outline of membrane recycling in general, this review summarizes previous data on membrane recycling in the collecting duct and related transporting epithelia and discusses some selected points relating to the role of membrane recycling and cell-specific function in the collecting duct.