The role of multidrug resistance protein 1 (MRP1) in transport of fluorescent anions across the human erythrocyte membrane.
We employed human red blood cells as a model system to check the affinity of MRP1 (Multidrug Resistance-associated Protein 1) towards fluorescein and a set of its carboxyl derivatives: 5/6-carboxyfluorescein (CF), 2',7'-bis-(2-carboxyethyl)-5/6-carboxyfluorescein (BCECF) and calcein (CAL). We found significant differences in the characteristics of transport of the dyes tested across the erythrocyte membrane. Fluorescein is transported mainly in a passive way, while active efflux systems at least partially contribute to the transport of the other compounds. Inside-out vesicle studies revealed that active transport of calcein is masked by another, ATP-independent, transport activity. Inhibitor profiles of CF and BCECF transport are typical for substrates of organic anion transporters. BCECF is transported mainly via MRP1, as proven by the use of QCRL3, a monoclonal antibody known to specifically inhibit MRP1-mediated transport. Lack of effect of QCRL3 on CF uptake excludes the possibility of MRP1 being a transporter of this dye. No inhibition of CF accumulation by cGMP, thioguanine and 6-mercaptopurine suggests also that this fluorescent marker is not a substrate for MRP5, another ABC transporter identified in the human erythrocyte membrane.
Rychlik
B
B
Department of Molecular Biophysics, University of Łódź, Banacha 12/16, 90-237 Łódź, Poland. brychlik@biol.uni.lodz.pl
Balcerczyk
A
A
Klimczak
A
A
Bartosz
G
G
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000097:blood*; D000838:Anions; D004910:Erythrocyte Membrane / Q000378:metabolism*; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006801:Humans; D066298:In Vitro Techniques; D017136:Ion Transport
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000838:Anions; D005452:Fluoresceins; D005456:Fluorescent Dyes; C024098:6-carboxyfluorescein; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; C007740:fluorexon