The liver is quantitatively the most important site of glutathione synthesis. It plays a central role in providing glutathione for cellular protection against reactive metabolic intermediates and pollutant xenobiotics, and in supplying plasma glutathione for inter-organ glutathione metabolism. Hepatic glutathione turnover is accounted for almost exclusively by the efflux of reduced glutathione (GSH), Of glutathione disulfide (GSSG), and of glutathione conjugates (GSH-thioethers and thioesters) into bile and plasma. Recent studies demonstrate that greater than 50% of the glutathione released by the rat liver is secreted into canalicular bile. However, within the biliary tree, glutathione is extensively degraded by the enzymes gamma-glutamyl transferase and peptidases, so that only a small fraction of the glutathione secreted by liver cells is found in its intact form in excreted bile. Some of glutathione's catabolic products are reabsorbed from bile. The functions of this intrahepatic cycle are unknown. The overall objectives of the proposed studies are to characterize the mechanisms of transport, and the physiological functions f the hepatobiliary metabolism of glutathione. Using purified rat liver cancalicular and basolateral plasma membrane vesicles, the specific aims are to 1) establish the criteria for GSH transport in these two membrane domains, 2) examine whether specific transport processes exist on canalicular membranes for the transport of cysteine-S-conjugates, and 3) evaluate the role of GSH in protecting liver plasma membranes from oxidant challenge. Using the isolated perfused rat liver preparation, 1) identify the factors that modulate the GSH/GSSG ratio in bile, and the rate of glutathione efflux into the perfusate, 2) examine whether the glutathione redox status in bile is a determinant of the permeability of the biliary tree, 3) test the hypothesis that secretion of GSH into bile is a primary driving force in the formation of canalicular bile, and 4) determine the role of membrane potential in the transport of GSH into bile and plasma. The cellular and subcellular distribution of hepatic gamma- glutamyl transferase will be examined immunohistochemically using two heterologous antibodies to the enzyme, under a series of conditions that are known to modulate hepatic gamma-glutamyl transferase activity.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
First Independent Research Support & Transition (FIRST) Awards (R29)
Project #
5R29DK039165-04
Application #
3463057
Study Section
General Medicine A Subcommittee 2 (GMA)
Project Start
1987-08-01
Project End
1992-07-31
Budget Start
1990-08-01
Budget End
1991-07-31
Support Year
4
Fiscal Year
1990
Total Cost
Indirect Cost
Name
University of Rochester
Department
Type
Schools of Dentistry
DUNS #
208469486
City
Rochester
State
NY
Country
United States
Zip Code
14627
Ballatori, N (1994) Glutathione mercaptides as transport forms of metals. Adv Pharmacol 27:271-98
Hinchman, C A; Ballatori, N (1994) Glutathione conjugation and conversion to mercapturic acids can occur as an intrahepatic process. J Toxicol Environ Health 41:387-409
Ballatori, N; Dutczak, W J (1994) Identification and characterization of high and low affinity transport systems for reduced glutathione in liver cell canalicular membranes. J Biol Chem 269:19731-7
Dutczak, W J; Ballatori, N (1994) Transport of the glutathione-methylmercury complex across liver canalicular membranes on reduced glutathione carriers. J Biol Chem 269:9746-51
Hinchman, C A; Truong, A T; Ballatori, N (1993) Hepatic uptake of intact glutathione S-conjugate, inhibition by organic anions, and sinusoidal catabolism. Am J Physiol 265:G547-54
Ballatori, N; Truong, A T (1992) Glutathione as a primary osmotic driving force in hepatic bile formation. Am J Physiol 263:G617-24
Ballatori, N; Boyer, J L (1992) Taurine transport in skate hepatocytes. I. Uptake and efflux. Am J Physiol 262:G445-50
Dutczak, W J; Ballatori, N (1992) gamma-Glutamyltransferase-dependent biliary-hepatic recycling of methyl mercury in the guinea pig. J Pharmacol Exp Ther 262:619-23
Simmons, T W; Anders, M W; Ballatori, N (1992) L-cysteine and S-(1,2-dichlorovinyl)-L-cysteine transport in rat liver canalicular membrane vesicles: potential reabsorption mechanisms for biliary metabolites of glutathione and its S-conjugates. J Pharmacol Exp Ther 262:1182-8
Ballatori, N (1991) Mechanisms of metal transport across liver cell plasma membranes. Drug Metab Rev 23:83-132

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