ROLE OF H+/HCO3- TRANSPORT IN BILE FORMATION

The formation of bile is an important yet poorly understood hepatic function. Bile formation begins at the level of the canaliculus and recent studies by the applicant and others suggest that formation of canalicular bile results, in part, from active transport of HCO3- by hepatocytes. Ducts and ductules are also believed to contribute to bile formation via secretion of a HCO3-- rich fluid, yet little is known regarding the mechanism(s) or regulation of ductular secretion, largely because of the lack of an appropriate experimental model. This proposal outlines studies, base on recent observations by the Principal Investigator, which relate generally to mechanisms of solute and water movement by liver and focus specifically on the roles of H+ and HCO3-transport in bile formation by hepatocytes and ductular cells. The applicant proposes to (a) further characterize hepatic Na+/HCO3- symport, a previously unrecognized mechanism of hepatic HCO3- transport which he and his colleagues recently identified in hepatocytes, (b) test the hypothesis that hypercholeretic bile acids act, in part, by stimulating H+ and HCO3- transport by hepatocytes via mechanisms also involved in the regulation of intracellular pH (pHi), (c) define the relationship between intracellular pH and glucuronidation of bile acids, (d) develop a system for establishing bile ductular epithelial cells in primary culture, and (e) define the mechanism(s) of H+ and HCO3- transport present in ductular cells and determine the effects on these transport mechanism of choleretic agents believed to enhance ductular secretion. The studies will employ established methods and models and techniques recently developed by the applicant (e.g. fluorescence measurement of pHi in cultured hepatocytes), as well as models and techniques (e.g., primary cultures of hepatic ductular cells, measurement of pHi in individual hepatocytes or ductular cells) currently under development.