title: Interaction of multidrug-resistant Chinese hamster ovary cells with the peptide ionophore gramicidin D.
abstract: A major form of multidrug resistance results from the overexpression of P-glycoprotein, a 170 kDa membrane protein. Multidrug resistant (MDR) Chinese hamster ovary (CHO) cells and mdrl transfectants displayed cross-resistance to the channel-forming peptide ionophore gramicidin D, which was reversed by various chemosensitizers, thus directly implicating P-glycoprotein as the mediator of resistance. However, gramicidin D was not able to inhibit [3H]azidopine photolabelling of P-glycoprotein. MDR cells were not resistant to other pore-forming ionophores, but showed a modest level of cross-resistance to the mobile ionophore valinomycin. There was no difference in 125I-gramicidin D uptake by resistant and sensitive cells. Resistant cells showed lower 86Rb+ uptake, relative to the drug-sensitive parent. Addition of GmD increased both the rate and the level of 86Rb+ uptake in sensitive cells, but had no effect on MDR cells. MDR cells also showed much lower rates of gramicidin D-dependent 86Rb+ efflux than sensitive cells, and this was greatly increased by verapamil. These results suggest that P-glycoprotein interferes with the formation of ion-conducting gramicidin D channels. In contrast, valinomycin had the same effect on gramicidin D-dependent cation efflux in MDR and sensitive cells. Gramicidin D is thus unique among the ionophores is being a substrate for P-glycoprotein, which appears to greatly reduce the formation of active dimeric channels in the plasma membrane of MDR cells.
authors.affiliation: Guelph-Waterloo Centre for Graduate Work in Chemistry, Department of Chemistry and Biochemistry, University of Guelph, Ontario, Canada.
authors.forename: D W
authors.initials: DW
authors.lastname: Loe
authors.forename: F J
authors.initials: FJ
authors.lastname: Sharom
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000345:Affinity Labels; D000818:Animals; D016466:CHO Cells / Q000187:drug effects*; D002352:Carrier Proteins / Q000502:physiology*; D002455:Cell Division / Q000187:drug effects; D006224:Cricetinae; D003412:Cricetulus; D004351:Drug Resistance / Q000235:genetics; D006096:Gramicidin / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology*; D008562:Membrane Glycoproteins / Q000502:physiology*; D012414:Rubidium Radioisotopes / Q000378:metabolism; D014162:Transfection; D014700:Verapamil / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000345:Affinity Labels; D002352:Carrier Proteins; D007476:Ionophores; D008562:Membrane Glycoproteins; D012414:Rubidium Radioisotopes; D006096:Gramicidin; D014700:Verapamil