Abstract
We studied transepithelial transport of 3H-labeled hydrophobic cationic drugs in epithelia formed by wild-type and by drug-resistant Madin-Darby canine kidney (MDCk) cells that had been infected with a retrovirus carrying the multidrug-resistance (MDR1) cDNA which encodes the P-glycoprotein. P-glycoprotein is an ATP consuming plasma membrane multidrug transporter responsible for the efflux of cytotoxic chemotherapeutic drugs from resistant cancer cells. Wild-type MDCK cells have small amounts of P-glycoprotein detected by immunoprecipitation. Net transepithelial transport across wild-type MDCK epithelia was demonstrated. Basal to apical flux of 100 nM vinblastine was about six times higher than apical to basal flux. Addition of unlabeled vinblastine reduced basal to apical flux of tracer and increased apical to basal flux of tracer, a pattern expected if there is a saturable pump that extrudes vinblastine at the apical plasma membrane. Daunomycin, vincristine, and actinomycin D were also actively transported and at 20 microM these agents inhibited transport of vinblastine, suggesting that wild-type MDCK cells have a common transporter for all these drugs. Vinblastine transport was also inhibited by 20 microM verapamil, which inhibits the multidrug transporter and reverses multidrug-resistance in non-polarized cells. Net transepithelial transport of all these cytotoxic drugs and of verapamil was much higher in epithelia formed by MDCK cells infected with a human MDR1 virus (MDR-MDCK) which is expressed on the apical surface of MDR-MDCK monolayers. Because the transport of these cytotoxic drugs and verapamil is increased in MDR-MDCK epithelia compared to wild-type MDCK epithelia, transport in both these cell populations can be attributed to P-glycoprotein. These results are consistent with a role for P-glycoprotein in multidrug secretory transport across the epithelium of the proximal tubule since P-glycoprotein is normally expressed on the apical membrane of proximal tubule cells.
Highlights
We studied transepithelial transport of 3H-labeled ently acts as an energy-dependent transport system for nathydrophobi cc ationi cd r u g si ne pitheli af o r m e db y ural product cytotoxic drugs such as doxorubicin (Adriamywild-type and by drug-resistant Madin-Darby canine cin), vinblastine, and actinomycin D.In kidney (MDCk) cells that had been infected with a retrovirus carrying the multidrug-resistanc(eMDR1)
Addition of unlabeled vinblastine reduced basal that allows a specific ligand to enter theepithelial cells, and to apical flux of tracer and increased apical to basal the opposite plasma membrane contains a transporter that flux of tracear,pattern expected if thereis a saturable functions to export the ligand from the cell, resulting in net pump that extrudes vinblastine at the apical plasma transepithelial transport of the ligand from one side of the membrane
Net transepithelial transport aollf from the basal surface is likely to leave the cell across the thesecytotoxicdrugsandofverapamil was much apical plasma membrane, whereas ligand entering the cell higher in epithelia formed by McDelClsKinfected with a human M D R l virus(MDR-Madin-Darby canine kidney (MDCK))which is expressed onthe apical surface of MDR-MDCK monolayers
Summary
Vol 264, No 25, Issue of September 5,pp. 14880-148&1,1989 Printed in U.S.A. Transepithelial Transport of Drugs by the Multidrug Transporter in Cultured Madin-Darby Canine KidneyCell Epithelia*. Because the transport of these cytotoxic dru and verapamil is increased in MDR-MDCK epithelia compared to wild-type MDCK epithelia, transport in both these cellpopulationscan be attributed to Pglycoprotein These results are consistent with a role for P-glycoprotein in multidrug secretory transport across the apical plasma membrane is likely to leave the cell across the same plasma membrane, with the result that basal gbtose apical flux exceedsapical to basal flux. Resistance of cultured cells to multiple chemotherapeutic agents may result from expression of the MDRl gene This gene encodes a protein, termed P-glycoprotein, which apparnet basal to apical transport of [3H]vinblastine, vincristine, daunomycin and actinomycin D, a pattern anticipated if Pglycoprotein is polarized tothe apical plasma membrane (middle and left panels of Fig. 1). These results support the idea thatthe multidrug transporter is a major contributor to excretion of natural product cytotoxic drugs by kidney, liver, and intestine
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
