Cross-section analysis of most gallstones shows repeated cyclic patterns in stone composition suggesting that bile composition undergoes fluctuations during stone nidation and growth. The overall aim of this study is to examine the thesis that some proteins act consistently or intermittently as traps for calcium salts and cholesterol and provide a skeleton for stone nidation and growth. Biliary protein fractions will be identified, characterized and correlated with proteins in stones to identify mechanisms by which stone components precipitate. Biliary components that control this process will be assessed for their effect on protein binding of calcium salts in vitro and on stone composition in animals. This process will be examined in man to provide a relevent framework and in animals to provide reproducible and controllable conditions. The specific aims are to: 1. Determine the influence of biliary pH on stone growth by examining the distribution of the acidic and neutral salts of calcium bilirubinate in stone using Fourier Transform Infrared Spectroscopy (FTIR). 2. Examine, using FTIR, the composition of gallstone surfaces in comparison with the surrounding bile. Identify the microstructure and composition of cholesterol-calcium salt crystals using scanning electron microscopy-energy dispersive x-ray analysis (SEM-EDXA). Identify the distribution of proteins in stones using FTIR. 3. Use SEM-EDXA to examine stone microstructure and composition, stone porosity and protein-crystal interactions. 4. Use a gallbladder explant system to determine the effects of ionized calcium, bilirubinate and phosphate on mucin production and secretion. 5. Examine the effects of graded biliary stasis on gallbladder function, bile secretion and brown pigment stone formation and to examine the hypothesis that an acid microenvironment exists in bile during stone nidation and intermittently during stone growth. 6. Quantitate and characterize the calcium salt binding properties of proteins in bile and through mixing experiments to examine the nidation inhibition and promation properties of other biliary proteins separated using Fine performance liquid chromatography on gel filtration columns. The results of these studies will test the theory that a variety of proteins of different binding affinities, together with other protein acting as inhibitors or promoters, explains the unique proportions of cholesterol and calcium salts found in sets of gallstones from different patients.