title: Evidence for a role of the multidrug resistance protein (MRP) in the outward translocation of NBD-phospholipids in the erythrocyte membrane.
abstract: Phosphatidylserine (PS) containing a 7-nitrobenz-2-oxa-1, 3-diazol-4-yl- (NBD-) hexanoyl residue, like native PS, preferentially distributes into the inner membrane leaflet of human erythrocytes. In the case of NBD-PS, this preference results from two opposite active processes, an inward translocation mediated by the aminophospholipid flippase and an outward translocation mediated by an ill-defined floppase. Selective inhibition of this floppase by alkylating reagents or cationic and anionic drugs increases the extent of accumulation of NBD-PS in the inner membrane leaflet from about 70% in control cells to about 90%. Different inhibitor sensitivities of the flippase and the floppase strongly suggest that both represent different entities. The floppase was characterized in further detail by comparing inhibitory effects of various compounds on this translocase with their effects on known primary active transport systems for amphiphilic compounds. The inhibitory effects of various drugs, glutathione conjugates and GSSG on the floppase activity closely correlate with those reported for the active transport by the multidrug resistance protein (MRP) while only poorly going parallel with those for the active transport by the low affinity pump for glutathione conjugates and the multidrug resistance MDR1 P-glycoprotein. The NBD-phospholipid floppase activity of the erythrocyte is thus probably a function of MRP.
authors.affiliation: Institut für Physiologie, Universitätsklinikum, Pauwelsstrasse 30, D-52057 Aachen, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Kamp
authors.forename: C W
authors.initials: CW
authors.lastname: Haest
mesh_terms: D009327:4-Chloro-7-nitrobenzofurazan / Q000031:analogs & derivatives* / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000097:blood / Q000502:physiology*; D000477:Alkylating Agents / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002352:Carrier Proteins / Q000187:drug effects; D018432:Drug Resistance, Multiple; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000187:drug effects; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D010718:Phosphatidylserines / Q000378:metabolism*; D049294:Phospholipid Transfer Proteins; D013050:Spectrometry, Fluorescence
chemical_list: D009327:4-Chloro-7-nitrobenzofurazan; D018528:ATP-Binding Cassette Transporters; D000477:Alkylating Agents; D017301:Ca(2+) Mg(2+)-ATPase; D002352:Carrier Proteins; D005978:Glutathione; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D010718:Phosphatidylserines; D049294:Phospholipid Transfer Proteins; C034296:N-(7-nitro-2,1,3-benzoxadiazol-4-yl)phosphatidylserine; C086860:glutathione transporter