Hepatic glutathione plays a key role in detoxification, protecting against toxins and carcinogens. A poorly understood factor in the homeostasis of hepatic glutathione is its efflux from intracellular to extracellular across both the sinusoidal and canalicular surfaces. This proposal is aimed at a better understanding of the mechanism of hepatic glutathione efflux and its importance. Using the in situ perfused rat liver model, the following studies are proposed: 1) To determine the contribution of efflux to the turnover of hepatic glutathione and the pool(s) from which biliary and perfusate glutathione arise; 2) To determine the relative maturation of sinusoidal and canalicular glutathione efflux with development from young to adult rats; 3) To determine the differential effect of inducing agents, such as phenobarbital, on sinusoidal and canalicular efflux and glutathione turnover; 4) To determine the relationship between the efflux of oxidized and reduced glutathione; 5) To determine the role of Alpha-glutamyltranspeptidase in hepatic glutathione efflux. The evidence available suggests that glutathione efflux into bile may be carrier-mediated whereas this is less certain for sinusoidal efflux. To further understand the mechanism of biliary efflux, the kinetics of glutathione binding to canalicular enriched liver plasma membrane will be determined. The binding interaction of reduced and oxidized glutathione and the influence of inducing agents and the maturational process on the binding kinetics will be determined. The work proposed will define the contribution of glutathione efflux to hepatic glutathione turnover, examine the relationship between canalicular and sinusoidal efflux through studies of the maturation and induction of efflux, assess the relationship between the efflux of reduced and oxidized glutathione, and through binding studies, identify the putative canalicular carrier(s) for reduced and oxidized glutathione.
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