AJP - Cell Physiology, Vol 262, Issue 1 C104-C110, Copyright © 1992 by American Physiological Society
ATP-dependent multispecific organic anion transport system in rat erythrocyte membrane vesicles
M. Heijn, R. P. Oude Elferink and P. L. Jansen
Division of Gastrointestinal and Liver Diseases, Academic Medical Centre, Amsterdam, The Netherlands.
The uptake of oxidized glutathione (GSSG) into inside-out membrane vesicles
of Wistar rat erythrocytes was studied. Uptake was ATP dependent, into an
osmotically active space, and saturable. Analysis of saturable
ATP-dependent GSSG uptake showed two affinities for GSSG [concentration for
half-maximal velocity (K1/2 1), 26 microM; K 1/2 2, 4 mM; maximum transport
rate (Vmax 1), 100 pmol.mg-1.min-1; Vmax 2, 360 pmol.mg-1.min-1].
Interactions of the high-affinity system with different organic compounds
were studied. Leukotriene C4, bromosulfophthalein-S-glutathione, and
2,4-dinitrophenyl-S-glutathione were effective inhibitors. In addition,
anionic nonglutathione conjugates, like indocyanine green, rose bengal,
dibromosulfophthalein, and sulfated or glucuronidated (divalent) bile acids
inhibited GSSG transport. Monovalent bile acids had no influence on GSSG
transport. Inhibition by 2,4-dinitrophenyl-S-glutathione [inhibition
constant (Ki) = 2.6 microM] and sulfated glycolithocholic acid (Ki = 2.9
microM) was purely competitive. The use of adenosinetriphosphatase (ATPase)
inhibitors suggested a resemblance with E1E2-type ATPase. Vesicles of
erythrocytes isolated from the TR- rat, a mutant rat strain with a
defective biliary secretion of organic anions, have an impaired uptake of
GSSG (Vmax was decreased 2-fold). In conclusion, erythrocytes have an
ATP-dependent organic anion transport system that can be inhibited by a
broad range of organic anions. This system is very similar if not identical
to the hepatocanalicular ATP-dependent organic anion transporter.
