The plasma uptake and biliary elimination of lipophilic xenobiotics by the liver are regulated largely by membrane-bound transport proteins and intracellular transfer proteins. At the sinusoidal membrane of the hepatocyte, these compounds can either passively diffuse or be actively transported across the membrane. Once in the cell, soluble transfer proteins can prevent refluxing of the compound back into the plasma and can facilitate its transport to sites of metabolism and elimination. Ultimately, the compound or its metabolites may be eliminated from the cell into the bile duct via canalicular transport proteins. In the present study, we will investigate the involvement of various transfer and transport proteins in the uptake and elimination of pesticides by the liver. The in vitro binding of pesticides to various intracellular transfer proteins will be examined using photoaffinity labeling and other techniques. The physiological significance of the in vitro binding interactions between pesticides and proteins will then be examined by measuring the competitive inhibition of the photoaffinity labeling of transfer proteins by pesticides in intact mouse hepatocytes and in Daphnia magna which are physiologically conducive to in vivo photoaffinity labeling experiments. The sinusoidal transport of pesticides will be measured by constructing rightside-out sinusoidal membrane vesicles from mouse hepatocytes and measuring the active uptake of radiolabeled pesticide by the vesicles. Further, the involvement of intracellular transfer proteins in the uptake of pesticides will be determined by constructing vesicles """"""""loaded"""""""" with a particular purified transfer protein and using these vesicles to measure pesticide transport. The transport of pesticides across the canalicular membrane will similarly be examined by constructing inside-out canalicular membrane vesicles from mouse hepatocytes and measuring uptake of radiolabeled pesticides by these vesicles. Results from this study will significantly advance our understanding of the processes that govern the hepatic extraction of pesticides from the plasma and their biliary elimination.
| Bain, L J; McLachlan, J B; LeBlanc, G A (1997) Structure-activity relationships for xenobiotic transport substrates and inhibitory ligands of P-glycoprotein. Environ Health Perspect 105:812-8 |
| LeBlanc, G A; Bain, L J; Wilson, V S (1997) Pesticides: multiple mechanisms of demasculinization. Mol Cell Endocrinol 126:1-5 |
