Elevated Biliary Calmodulin During Gallstone Formation The Role of Bile Acids A. JAMES MOSER, MD, JOSEPH A. KARAM, MD, DAN I. GIURGIU, MD, PHILIP A. WEBER, MD, ZAHIDUR R. ABEDIN, BS, JOEL J. ROSLYN, MD, and MOHAMMAD Z. ABEDIN, PhD Hepatic bile synthesis is altered during experimental gallstone formation. In response to cholesterol, there is a hydrophobic shift in hepatic bile acid synthesis and hypersecretion of phospholipids. These changes decrease the vesicular capacity for cholesterol and favor crystallization. The mechanism for these changes in hepatic bile formation is unknown. Calmodulin (CaM), a Ca 21 receptor protein involve d in cellular secretion, regulates gall- bladder transport and may play an important role in alterations of hepatic bile formation during cholelithiasis. We hypothesized that biliary CaM activity is altered during gallstone formation and may be associated with changes in bile acid and phospholipid synthesis. Prairie dogs were fed either control ( N 5 22) or 1.2% cholesterol-enriched ( N 5 26) diets for one to six weeks. Cholecystectomy was performed; the common bile duct was cannulated, and hourly bile samples were collected. CaM was measured in bile and gallbladde r tissues by radioimmunoassay. Bile samples were analyze d for cholesterol, phospholipids, total bile acids, total protein, calcium, and individual bile acid composition. Compared to controls, gallstone animals had elevated hepatic bile levels of CaM, phospholipids, and cholesterol. Hydrophobic bile acid synthesis was also stimulated, with increased levels of tauroche node- oxycholic acid (TCDCA) and decreased taurocholic acid (TCA). Gallbladde r bile demon- strated similar changes. Although gallbladde r bile CaM levels were increased, tissue levels were unchanged, suggesting that increased CaM concentration is a hepatic phenomenon. Hepatic bile CaM activity correlated linearly with TCDCA concentration ( r 5 0.64, P , 0.004) and phospholipid hypersecretion ( r 5 0.53, P , 0.03). The relationship between biliary CaM and increased concentrations of TCDCA and phospholipids suggests a role for CaM in alterations of hepatocyte secretion that may promote gallstone formation. KEY WORDS: gallstones; calmodulin; bile acids; phospholipids; secretion; prairie dog. Calmodulin (CaM) is a ubiquitous Ca 21 binding pro- tein responsible for many regulatory activities of in- tracellular calcium ([Ca 21 ] ic ) (1). The Ca 21 ±CaM complex activates CaM-dependent protein kinase s that phosphorylate target proteins and alter their state of activation (2). Ussing chambe r studies suggest that CaM regulates ion transport by the gallbladde r epithelium (3). Ca 21 ±CaM has also been shown to mediate the fusion of secretory granules to the rat parotid plasma membrane, thereby modulating exo- cytosis (4). Recent data in isolate d hepatocyte culture demonstrates that taurocholic acid (TCA) increases Manuscript received February 15, 1997; revised manuscript re- ceived September 26, 1997; accepted September 29, 1997. From the Research and Surgical Services, Philadelphia VA Medical Center, and Department of Surgery, Allegheny University of the Health Sciences, Philadelphia, Pennsylvania. Financial support provided by the Department of Veteran’s Affairs Merit Review (J.J.R.) and an institutional grant from the Allegheny Health, Education, and Research Foundation (M.Z.A.) Address for reprint requests: Mohammad Z. Abedin, Depart- ment of Surgery, Allegheny University of the Health Sciences, 3300 Henry Avenue, Philadelphia, Pennsylvania 19129. Digestive Diseases and Sciences, Vol. 43, No. 1 (January 1998), pp. 170±177 170 Digestive Diseases and Sciences, Vol. 43, No. 1 (January 1998) 0163-2116/98/0100-0170$15.00/0 Ñ 1998 Plenum Publishing Corporation