Luckie DB, Krouse ME, Law TC, Sikic BI, Wine JJ. Doxorubicin selection for MDR1/P-glycoprotein reduces swelling-activated K+ and Cl- currents in MES-SA cells.
THE AMERICAN JOURNAL OF PHYSIOLOGY 1996;
270:C1029-36. [PMID:
8928730 DOI:
10.1152/ajpcell.1996.270.4.c1029]
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Abstract
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.
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