Doxorubicin selection for MDR1/P-glycoprotein reduces swelling-activated K+ and Cl- currents in MES-SA cells.
To test the hypothesis that P-glycoprotein enhances swelling currents through regulation of volume-sensitive Cl- channels [recently termed VSOAC (volume-sensitive osmolyte and anion channel)], a human uterine sarcoma cell line (MES-SA) and its doxorubicin-selected counterpart (Dx5) were studied. P-glycoprotein mRNA and protein levels were detected only in Dx5 cells. However, whole cell patch-clamp experiments showed that swollen Dx5 cells (n = 5) produced smaller VSOAC currents than MES-SA cells (n = 4; 106 +/- 26 pA/pF vs. 232 +/- 76 pA/pF at 90 mV). In radioisotopic efflux experiments, both swelling-activated 125I (Cl-) currents (n = 15) and 86Rb (K+) currents (n = 8) were found to be two-to fourfold smaller in the Dx5 (high P-glycoprotein) cells. Inhibitors of P-glycoprotein showed no specificity for the doxorubicin-selected cells (Dx5). Dideoxyforskolin (100 microM) blocked swelling-activated 125I efflux equally in both cell lines, whereas 100 microM verapamil had no effect. Thus, in this cell line, selection for P-glycoprotein expression is associated with reduced swelling currents. These findings suggest that P-glycoprotein expression does not directly facilitate VSOAC.
Luckie
D B
DB
Cystic Fibrosis Research Laboratory, Stanford University, California 94305, USA.
Krouse
M E
ME
Law
T C
TC
Sikic
B I
BI
Wine
J J
JJ
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D001826:Body Fluids / Q000378:metabolism*; D002712:Chlorides / Q000502:physiology*; D005576:Colforsin / Q000031:analogs & derivatives / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology*; D018432:Drug Resistance, Multiple; D004553:Electric Conductivity; D005260:Female; D006801:Humans; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D013267:Stilbenes / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002712:Chlorides; D012333:RNA, Messenger; D013267:Stilbenes; D005576:Colforsin; C022306:4,4'-dinitro-2,2'-stilbenedisulfonic acid; D004317:Doxorubicin; D014700:Verapamil; C047983:1,9-dideoxyforskolin; D011188:Potassium