AJP - Gastrointestinal and Liver Physiology, Vol 250, Issue 2 236-G243, Copyright © 1986 by American Physiological Society
Kinetics of glutathione efflux from isolated rat hepatocytes
T. Y. Aw, M. Ookhtens, C. Ren and N. Kaplowitz
The characteristics and kinetics of glutathione (GSH) efflux were examined
in homogeneous suspensions of freshly isolated rat hepatocytes. GSH efflux
was measured as its linear accumulation in the suspension medium.
Appearance of GSH extracellularly was reflected in a quantitative loss in
cellular GSH. However, the total GSH remained essentially unchanged,
indicating minimal net synthesis of GSH under these experimental
conditions. GSH efflux was sensitive to temperature, with a calculated Q10
value of 2.3. A wide range of cellular GSH concentration ranging from near
complete and moderate depletion to severalfold the control values was
achieved by treatment of animals or cells with various GSH depletors or
inducers. At physiological (fed) and elevated (3-methylcholanthrene- and
CoCl2-induced) cellular GSH, the rate of GSH efflux was near maximum. The
rate fell dramatically to 50% maximum at a GSH concentration equaling 35
nmol/10(6) cells. A 48-h fast resulted in a 40% loss of cellular GSH, with
a corresponding decrease in efflux rates. Addition of GSH to the incubation
medium had no effect on efflux rates. The relationship of GSH efflux to
cellular GSH concentration was characterized by apparent sigmoidal
saturation kinetics. The data were fitted well by the Hill model with the
following kinetic parameters: Vmax = 0.25 nmol X 10(6) cells-1 X min-1, Km
= 3.5 mM, and n = 3. These results correspond very closely to our previous
findings in the perfused liver.
