Kinetic analysis of the mechanism of action of the multidrug transporter.
To clarify the mechanistic role of PGP (P-glycoprotein) in multidrug transport, we constructed a kinetic model composed of four compartments: (1) the extracellular space; (2) the space in the membrane; (3) the intracellular space; and (4) the pore-like space in the PGP molecule. The kinetics of the concentration of ADM (adriamycin) in each compartment were formulated based on the assumptions that (a) the movement of ADM between two compartments by diffusion is dependent on a dynamic distribution coefficient introduced here, (b) the uptake of ADM into the pore-like structure by the pump mechanism activated by ATP is described by enzyme kinetics, (c) the movement of ADM out of the pore-like structure to the extracellular medium through a valve-like mechanism is also expressed by enzyme kinetics. The mathematical analysis of the exact solution can explain the distinct effects of verapamil and vanadate on the accumulation and release of ADM, where verapamil inhibits the efflux by the valve-like mechanism and vanadate blocks the influx by the pump mechanism. We also performed a numerical calculation with this model for a quantitative explanation and found the valid parameter values to fit the experimental data. These results support the modified hydrophobic vacuum cleaner model.
Ashida
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H
Division of Biomedical Information Sciences, National Defense Medical College Research Institute, Saitama 359-8513, Japan.
Oonishi
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T
Uyesaka
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N
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000903:Antibiotics, Antineoplastic / Q000493:pharmacokinetics*; D002121:Calcium Channel Blockers / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002477:Cells / Q000378:metabolism*; D004058:Diffusion; D004317:Doxorubicin / Q000493:pharmacokinetics*; D004789:Enzyme Activation; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism; D008954:Models, Biological; D014638:Vanadates / Q000378:metabolism; D014700:Verapamil / Q000378:metabolism
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000903:Antibiotics, Antineoplastic; D002121:Calcium Channel Blockers; D014638:Vanadates; D004317:Doxorubicin; D000255:Adenosine Triphosphate; D014700:Verapamil