The long-range objective of the proposed research is, as in previous years, to develop a better understanding of transport across epithelial membranes. Substances transported across epithelial must cross at least two barriers in series, the mebranes at the two sides of the cell layer, and there is ample evidence indicating that these barriers have different functional properties. Studies will be directed toward obtaining information on the properties of these individual barriers in frog skin, mammalian intestine and toad colon and on understanding the way in which these barriers contribute to overall epithelial function. We hope to obtain much more detailed information on transport systems for sodium, amino acids and sugars located in the individual barriers and to develop a better understaning of molecular mechanisms involved. The mode of energy input and details of coupling between different transport processes and between transport and metabolism is being examined. Studies will also be directed toward clarifying the relationship between membrane transport in epithelia and membrane structure as revealed by freeze-fracture electron microscopy. Thus the functional significance of vasopressin-induced intramembranous particle aggregates found in membranes of the toad bladder will be studied by correlation of their frequency with specific functional changes and by utilizing the deep-etching technique. Assessment will also be made of the extent to which similar vasopressin-induced membrane structural changes exist in other epithelia known to respond to vasopressin. The effect of aldosterone on membrane structure and vasopressin-induced structural alterations will also be examined.