title: A kinetic study of Rhodamine123 pumping by P-glycoprotein.
abstract: The MDR1 P-glycoprotein (P-gp) actively extrudes a wide variety of structurally diverse cytotoxic compounds out of the cell, is widely expressed in the epithelial cells of kidney, liver and intestine, and in the endothelial cells of brain and placenta, and plays an important role in drug resistance. We measured the accumulation of Rhodamine 123 (Rho123), a substrate of P-gp, into a drug sensitive and a drug resistant strain of the human leukemia cell line K562, as function of Rho123 concentration. With the aid of a mathematical transformation, we used the accumulation of Rho123 into the sensitive cells as a surrogate measure for the internal concentration of the probe in the resistant cells, and were thus able to measure the kinetic parameters of drug efflux pumping by P-gp. Drug pumping was half-saturated at an external Rho123 concentration of 7.2E-06+/-1.1E-06 M, and displayed a co-operative behaviour with a Hill number of 1.94+/-0.32. Verapamil could be shown to inhibit Rho123 efflux uncompetitively.
authors.affiliation: Laboratory of Pharmaceutical Resource Discovery, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
authors.forename: Yulin
authors.initials: Y
authors.lastname: Wang
authors.forename: DaCheng
authors.initials: D
authors.lastname: Hao
authors.forename: Wilfred D
authors.initials: WD
authors.lastname: Stein
authors.forename: Ling
authors.initials: L
authors.lastname: Yang
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000737:chemistry / Q000378:metabolism*; D000465:Algorithms; D006801:Humans; D020014:K562 Cells / Q000378:metabolism; D007700:Kinetics; D020112:Rhodamine 123 / Q000737:chemistry / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D020112:Rhodamine 123; D014700:Verapamil