Objective of the proposed research program is to elucidate the mechanism of antidiuretic hormone (ADH) action on kidney in health and disease. Special emphasis will be focused on the question how cyclic AMP formed in cells of distal tubules under influence of ADH regulates water permeability. The basis for these studies is hypothesis, that 1) water permeability of lumenal plasma membrane is associated with the specific membrane protein and that cyclic AMP influences this membrane by phosphorylation or other modifications of this specific membrane protein component and 2) that cytoplasmic microtubules are essential for cellular action of ADH and play a role in regulation of water permeability by cyclic AMP. Specific objectives are to investigate: a. Effect of ADH and cyclic AMP on phosphorylation and dephosphorylation of plasma membrane and microtubular proteins. b. Influence of ADH and cyclic AMP on polymerization and turnover of cytoplasmic microtubules. c. Relationship between protein phosphorylation and function of microtubules. d. Relationship between cyclic AMP dependent protein phosphorylation, status of microtubules and water permeability of membrane. Studies will be performed on cell-free systems to analyze individual components of proposed mechanism (enzymes, substrates, activators, inhibitors, polymerization of microtubules) and whole cells systems such as tissue slices and on kidneys in intact animals. Investigation will be conducted on normal kidneys and on kidneys of animals with inherited or drug-induced nephrogenic diabetes insipidus in search for the defect in cellular action to ADH in this disease. Based on these results experimental pharmacotherapy of nephrogenic diabetes insipidus will be developed.